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Stable and Color-Tailorable White Light From Blue LEDs Using Color-Converting Phosphor-Glass Composites
Journal of the American Ceramic Society
Abstract
Commercial Ce3+:YAG phosphors were embedded in glass frits. Thermal condition for the viscous sintering of the composite materials was optimized. The phosphor–glass composites had maximum external efficiency of 30% and maximum light extraction efficiency of 39%. Color temperatures of the composites composed of fluorescent glass frits containing Eu3+ and Mn2+ combined with blue LEDs shifted from ~7000 to ~4000 K.
... Finally, the BSZ glass coating was sintered at different temperatures (575, 600, 625, 650, and 700°C) in the air. To fabricate PiG coating, BSZ glass powder was mixed with different phosphor concentrations (30,35,40,45, and 50 wt %). The PiG coating was sintered at 600°C. ...
... In Fig. 3, it is shown that refractive index of the glass matrix at 460 nm is *1.82, which is similar to that of the YAG:Ce phosphor (1.83). The light efficiency loss by total internal reflection at the interface is closely related to the difference of refractive index between the glass matrix and the phosphor [34,35]. To achieve higher refractive index than that of most of the normal glass (1.5-1.6), ...
... The photoluminescence excitation (PLE) and photoluminescence (PL) spectra of PiG coatings with various phosphor concentrations (30,35,40,45, and 50 wt%) are plotted in Fig. 6a. There are two broad excitation bands peaked at 340 and 460 nm in the PLE spectra (k em = 540 nm), which are ascribed to the transitions of Ce 3? from the 4f ground states to the 5d states [44][45][46]. ...
The coating of phosphor-in-glass with high refractive index was successfully fabricated for enhanced light extraction efficiency of white LEDs through a multilayer screen-printing and low-temperature sintering procedure. The effects of sintering temperature on the B2O3–SiO2–ZnO glass coating and YAG:Ce phosphor concentration on the phosphor-in-glass coating were investigated. The B2O3–SiO2–ZnO glass matrix possesses low glass transition temperature and appropriate thermal expansion coefficient. With the addition of La2O3 and WO3, high refractive index of 1.82 at 460 nm is acquired. The amorphous glass coating, sintered at 600 °C, yields an optimized transmittance of 50%. Furthermore, negligible thermal degradation is observed in the phosphor-in-glass coating, and the emission peak under the 460-nm excitation is at ~540 nm. When increasing the concentration of phosphor, luminous efficacy and correlated color temperature are both improved, but color rendering index is deteriorated. As the refractive index increases, the light extraction efficiency of white LEDs is enhanced due to the reason that the match of refractive index between the glass matrix and the phosphor decreases the total internal reflection at the interface.
... Various inorganic materials have been extensively studied as alternatives to replace the organic resin. Some of them, like phosphor in glass (PiG), have recently been commercialized and are being used for high-power applications [3][4][5]. PiGs use transparent glass powders to embed ceramic phosphors and have demonstrated long-term durability with improved thermal and chemical stability compared to organic resins [5][6][7][8][9]. However, they require additional processing such as melting, pulverizing, sintering, and polishing before they can be applied to the LED as a color converter. ...
BaF2–Al2O3–B2O3–SiO2 glasses and glass-ceramics doped with Eu³⁺-Tb³⁺ were fabricated as an inorganic color converter for white LEDs. The BaF2–Al2O3–B2O3 glass composition was modified by adding SiO2, and thermal and mechanical stability improved with increasing SiO2 content while maintaining a quantum yield (QY) as high as 91%. To realize white color coordinates, Tm³⁺ was additionally introduced at varying contents, and Eu³⁺ content was also controlled. Excellent chromatic properties, such as a pure white color coordinates (x = 0.33, y = 0.33) with a co-related color temperature of 5772K, and a color rendering index (CRI) of 91 under 370 nm excitation, were successfully achieved. After the glass was heat-treated at 600 °C to fabricate a glass ceramic, the glass-ceramics were mounted on top of a 370 nm UV-LED, successfully demonstrating a white LED with nearly pure white color coordinates and a high CRI of 86. The increased emission intensity in the glass-ceramic was attributed to the formation of BaF2 crystals which were investigated by X-ray diffractometer (XRD) and a transmission electron microscope with energy dispersive spectroscopy (TEM-EDS).
... 1,2 As an alternative, inorganic color converters such as phosphor in glass (PiG) have recently been commercialized and are being used for high-power applications. [3][4][5] PiGs use transparent glass to embed ceramic phosphors and this ensures their improved thermal stability and long-term stability. [5][6][7][8][9] However, PiGs require a proper combination of glass matrix and phosphor powders to avoid possible reactions and the thermal degradation of the phosphors during the fabrication process. ...
SiO2‐Na2O‐Al2O3‐LaF3 glass‐ceramics doped with Eu²⁺ were synthesized as an efficient inorganic color converter for 400 nm UV‐LED. When Eu²⁺ formed within the glass matrix, the obtained glass showed cyan emission under 400 nm excitation, but its emission peak drastically shifted to greenish yellow upon heat treatment. With heat treatment the glass‐ceramic also showed highly increased emission intensity, and the color coordinate of the glass‐ceramic shifted to yellow. When it was mounted on top of a 400 nm UV‐LED, it demonstrated high color conversion efficiency and practical feasibility as an UV‐LED color converter. To vary the color coordination the heat‐treatment conditions and the thickness of the glass‐ceramic were adjusted. The resulting ceramic showed a high quantum yield of up to 78%, which is comparable to conventional ceramic phosphors. The spectral change in the glass‐ceramic is attributed to the formation of nepheline and LaF3 crystalline phases. X‐ray diffractometer (XRD), transmission electron microscope with energy dispervise spectroscopy (TEM‐EDS) and cathode luminescence (CL) were used to investigate the mechanism of Eu²⁺‐doped nepheline crystal formation, and its effect on the spectral change with heat treatment.
... Rare Earth (RE) doped glasses are emerging as promising luminescent and dosimetric materials for several applications like LCD displays, visible light emitting diodes, solid state lasers, fiber amplifier, dosimeters and scintillators [1][2][3][4][5][6][7][8]. These glasses are easily moldable and are more stable in various thermal, mechanical and chemical environments compared to crystalline phosphors [9,10]. ...
Interaction of 10ZnO-5Na2O-10Bi2O3-74.3B2O3-0.7Eu2O3 glasses exposed to high dose gamma rays were investigated using XRD, FTIR, absorption, photoluminescence followed by thermally and optically stimulated luminescence studies. XRD analysis confirmed the amorphous nature of glasses post-irradiation. Variation in FTIR spectra revealed, structural deformation of borate groups as a result of high dose gamma irradiation. Enhanced glass absorbance and red shift in absorption edge were observed with the increase in gamma dose. Further, radiation-induced absorption coefficient confirmed the trapped charges in the forbidden energy gap supported by Tauc’s plot and Urbach energy. Photoluminescence (PL) study demonstrated quenching of luminescence intensity at higher gamma doses. Lifetime of metastable 5D0 state of Eu3+ ions were estimated by the decay curves and color purity was calculated using 1931 CIE chromaticity coordinates (x,y).Thermally and optically stimulated luminescence studies reassured the existence of charges in trap centers due to irradiation. TL glow curve exhibited two broad emission peaks with the
corresponding temperature being at 490 K and 625 K. Distinct TL peaks of the material and their kinetic parameters (E, S, and b) were determined via Computerized Glow Curve Deconvolution (CGCD) method. Linear behavior obtained through the dose response of the glass (0.25 kGy – 3 kGy) proved their suitability for dosimetric application in the foodirradiation zones in addition to red LEDs (< 1 kGy).
... In addition, to improve the LED efficiency, it is possible to substitute organic silicone, which is used to fix the phosphor powder on the GaN crystal, with inorganic glasses. A such composite which consists of the crystal YAG:Ce powder distributed in the glass is usually referred to as phosphor-in-glass [6,7]. Low scattering is one of the main requirements for such composites. ...
... Tunable emission color by varying the Sm 3+ concentration was achieved because of the energy transfer from Eu 2+ to Sm 3+ ions. Yi et al. 73 reported on PiG prepared from a mixture of YAG:Ce 3+ phosphor and high-refractive-index glass frits containing Eu 3+ and Mn 2+ ions. The CCT of the emitted white light was shifted from ∼7000 K to 4244 K by controlling the concentration of Eu 3+ ions in the YAG:Ce 3+ -based PiG. ...
In the past decades, solid-state lighting based on phosphors as energy converters has been a fast-growing industry. Phosphorconverted white light-emitting diodes (pc-wLEDs) enable high-power applications and miniaturization; for this, the phosphor must have good stability and high efficiency. In order to satisfy this demand, phosphor plates have been proposed instead of conventional organic-based phosphor binders. In this review, such phosphor plates are categorized according to their synthesis methods, and the advantages and disadvantages of each category are detailed. In addition, we describe the major aspects of phosphor plates that require improvement for applications in high-power devices. For the fabrication of high-power LEDs, the phosphor configuration, color purity, porosity, and particle size of glass powders are key properties to enhance the luminescence efficiency and reduce the generation of heat inside wLED packages, thereby improving thermal stability.
... Attempts to overcome this problem include using various inorganic materials, such as phosphor ceramics [4], glass ceramics [5], and phosphor-in-glasses (PIGs) [6] with good thermal and chemical resistance to replace the commercially used organic encapsulants. Among these materials, PIG is attracting attention for its simple and easy color adjustment ability and ease of fabrication. ...
Phosphor-in-glass (PIG) has been attracting attention as a stable encapsulant for light-emitting diodes. However, the influence of the phosphor size and content on the morphology and optical properties of PIG must be further studied to achieve the desired color properties by understanding the relationship between the phosphor mixing conditions and the morphology. In this study, two different sizes of YAG:Ce3 + phosphors were used in different ratios and total amounts. The optical properties of the PIG samples were measured using an integrating sphere and UV-spectrometer, and cross-sectional scanning electron microscopy images were used to analyze the pore properties. The optical properties of PIG showed linear trends as functions of the pore and phosphor distributions, both of which affect the passage of light. This research shows that the desired color properties can be achieved in PIG by considering the phosphor mixing conditions and the related variations in the morphology.
... It is well known that the emission of Eu 2+ ion in solid state compound is generally originated from the transition 4f 6 5d→4f 7 [2,4]. The intensity of the signal emitted increase with the heat treatment temperature being the maximum at 1250 C and decrease at 1300°C. ...
Strong emission of green light in ceramic glass was obtained. The intensity of the
emitted signal changes with the heat treatment temperature.
... Mostly glasses with high refractive indices and low T g are used; on the one hand to match the refractive index to the phosphor to limit light scattering and, on the other hand, to allow low sintering temperatures in order to minimize chemical reactions of phosphor and glass. These glass compositions include tellurite [12,13,16,17], antimony borate [13,14], lead boro-silicate [15], barium boro-silicate [18] and zinc boro-silicate glasses [19,20]. Tin phosphate glasses with extremely low T g might also be interesting embedding materials, especially for thermally unstable phosphors [21]. ...
Commercial Ce³⁺ doped yttrium aluminum (Ce³⁺:YAG) and lutetium aluminum garnet (Ce³⁺:LuAG) powders were mixed with powdered soda-lime silicate glass with the molar composition 15.5 Na2O / 10.7 CaO / 73.8 SiO2. Then the mixtures were sintered at temperatures in the range from 800 to 1000 °C for 10 and 30 min. XRD-patterns proved that the samples contain only the respective garnet phases. During sintering at 1000 °C, a notable dissolution of the garnet phase took place as proved by the occurrence of the typical blue emission of Ce³⁺ in the glassy phase if excited with UV light. Dissolution of the phosphors is much lower at a processing temperature of 800 °C. Additionally, the dissolution process is strongly affected by the chemical composition of the glass. The concentration of the phosphors in the glass matrix had only a minor effect on the fluorescence intensity. The efficiency in lm/W increases with the sample thickness and is for the Ce³⁺:LuAG sample nearly as high as for polymer embedded samples, while it is slightly smaller for the Ce³⁺:YAG samples.
... 41 In addition, Yi et al. doped Eu 2+ and Mn 2+ into the glass matrix to compensate for the red emission, but they used PbO-based glass and the color tuning effect was not satisfactory because of the limited quantum efficiency of Eu 2+ /Mn 2+ ions for practical applications. 42 Worthy to be noticed, such design of mixing multiple phosphors in glass randomly will reduce the emission efficiency through large spectral overlapping caused by the partial re-absorption of emitted light by another phosphor, and result in low color purity. 43 As revealed in Fig. 7a, major part of the Ce:LuAG green emission was reabsorbed by the Eu:CASN red phosphor, and, in turn increased the red region, which affects the color purity and emission efficiency. ...
A series of Cr3+-doped transparent bulk glass ceramics embedded with LiGa5O8, Ga2O3 or ZnGa2O4 nanocrystals were fabricated as the alternatives for Cr3+-doped single-crystals to explore their possible application in fluorescence lifetime based temperature sensing. X-ray diffraction, transmission electron microscopy and optical spectroscopy were adopted to investigate their microstructure and luminescent behaviors. Impressively, the decay lifetimes of these glass ceramic samples were found to be highly temperature-sensitive, attributing to the competition of radiation transitions from the thermally coupled Cr3+2E state with a long lifetime and 4T2 one with a short lifetime. Finally, such temperature-dependent luminescence of Cr3+ was successfully interpret by a two-level kinetic model, which gives a highest temperature sensitivity of 0.76%K-1 (at 295K), 0.46%K-1 (at 370K) and 0.58%K-1 (at 420K) for the Cr3+-doped LiGa5O8, Ga2O3 and ZnGa2O4 glass ceramics, respectively.
... Glass materials have been proposed as alternative binders for phosphor powders to alleviate the thermal degradation of polymer resins. Phosphor-in-glass composites (PiGs) have higher efficiencies than do polymer-based mixtures [5][6][7]. ...
ZrO 2 light diffuser layers was placed on phosphor-in-glass composites (PiGs) to improve color uniformity of white-light-emitting diodes (white LEDs). Color coordinates of central part and periphery of white LEDs were (0.34, 0.38) and (0.36, 0.43), respectively; difference between two area decreases with the introduction of a diffuser layer. Color temperature difference also decreased from 770 to 464 K. The addition of diffuser layers reduced the luminous efficacy of the white LEDs from 90.3 to 83.4 lm/W.
... Inorganic glass-ceramic (GC), a kind of composite with Ce: YAG micro-crystals distributing among glass matrix, exhibits excellent thermal resistance and easy formability, and may simultaneously play the same key roles of luminescent convertor and encapsulating material as the traditional phosphor powder and organic resin respectively used in WLEDs. [11][12][13][14][15][16][17][18][19][20][21][22][23] Recently, we have adopted a low-temperature co-sintering technique to fabricate transparent Ce: YAG GC with QY higher than 90%. 24,25 In this method, Ce: YAG commercial phosphors were thoroughly mixed with the specifically designed inorganic TeO 2 -based or Sb 2 O 3 -based glass powders, and sintered at an optimal temperature at which the glass components were melted while the phosphor powders retained solid as much as possible. ...
Transparent glass-ceramics containing Ce3+: Y3Al5O12 phosphors and Eu3+ ions were successfully fabricated by a low-temperature co-sintering technique to explore their potential application in white light-emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X-ray spectroscopy. The impact of co-sintering temperature, Ce3+: Y3Al5O12 crystal content and Eu3+ doping content on optical properties of glass-ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass-ceramics, where Ce3+ ions located in YAG crystalline phase while the Eu3+ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce3+: 5d4f transition and red luminescence originating from Eu3+: 4f4f transitions. As a result, the quantum yield of the glass-ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.
... Studies on enhancing the luminescence characteristics of PIG used in LED packages have focused on varying the glass composition and thickness and the phosphor/glass ratio [9][10][11], and on increasing light extraction efficiency by reducing the refractive index gap between glass matrix and phosphor [12][13][14]. Transparency, however, is also an important parameter of LED encapsulants because the color converter transmits blue and yellow wavelengths emitted from the LED chip and yellow-emitting phosphor, respectively [15]. Increasing the transmittance of sintered glass turns out to be strongly related to minimizing the residual porosity [16][17][18] and the associated light scattering in the matrix, thereby enhancing PIG luminous efficacy. ...
The transmittance of phosphor-in-glass (PIG) color converter material was studied as a factor affecting the luminescence properties of light emitting diode packaging; it is closely related to the residual pores of sintered glass. In this study, the correlation between porosity and optical properties of the glass and PIG plates was investigated. The transmittance, luminescence properties, and porosity were measured by UV-visible spectrometer, integrating sphere and scanning electron microscope, respectively. Transmittance of the sintered glass plate and the luminous efficacy of the PIG plate both increase with decreased porosity, while the light scattering coefficient decreases. Luminescence properties such as emission intensity and color coordinates are also influenced by transmittance of the PIG plate.
... 41 In addition, Yi et al. doped Eu 2+ and Mn 2+ into the glass matrix to compensate for the red emission, but they used PbO-based glass and the color tuning effect was not satisfactory because of the limited quantum efficiency of Eu 2+ /Mn 2+ ions for practical applications. 42 Worthy to be noticed, such design of mixing multiple phosphors in glass randomly will reduce the emission efficiency through large spectral overlapping caused by the partial re-absorption of emitted light by another phosphor, and result in low color purity. 43 As revealed in Fig. 7a, major part of the Ce:LuAG green emission was reabsorbed by the Eu:CASN red phosphor, and, in turn increased the red region, which affects the color purity and emission efficiency. ...
Currently, the major commercial white light-emitting diode is the phosphor converted LED made of blue-emitting chip and Y3Al5O12:Ce3+ yellow phosphor dispersed in organic silicone. However, the organic binder in high-power device ages easily and turns yellow due to accumulated heat emitted from chip, which adversely affects the device properties such as luminous efficacy and color coordination, and therefore reduces its long-term reliability as well as lifetime. In this mini-review article, we provide an overview of recent progresses in developing transparent inorganic glass–ceramics phosphors excitable by blue chip, as an alternative to conventional polymer-based phosphor converter, for construction of high-power white light-emitting diodes. Two kinds of synthesis routes, glass crystallization and low-temperature co-sintering, are discussed in detail. Afterwards, the materials design, structure/property optimization as well as glass–ceramic-based WLED devices construction are summarized. Finally, challenges and future advances for the realization of transparent glass–ceramics in commercial applications will be presented.
The main focus of laser lighting research has been on perfectly combining fluorescent conversion materials with laser light sources to improve luminous efficiency (LE). In this paper, the high refractive index, high transmittance and low sintering temperature of tellurite glass is combined with the thermal stability and mechanical strength of germanate glass，which is innovatively used as a matrix for phosphor-in-glass (PiG). The use of high valent ions as modifiers reduces the diffusion and mobility of ions to reduce the erosion of phosphors and protect the luminescent performance of phosphors. By changing Ge/Te ratio, the glass maintains 80% transmittance, and the refractive index decreases from 1.97 to 1.83 matching that of the YAG phosphor. The increase in GeO2 improves the thermal stability and mechanical strength of the glass, thereby improving the fluorescence intensity (approximately 1.6%) at 473 K and the luminous flux by up to 12.8%. The best PiG sample had a LE of 230 lm/W and excellent internal quantum efficiency (IQE) of 85.3%, achieving high levels of luminescence. Adding different phosphor contents can achieve the role of adjusting the correlated color temperature (4500–6000 K), and the color coordinates (0.322, 0.330) are close to the ideal white light. These results show that tellurite-germanate glass can be used as a good carrier for fluorescence conversion materials, which brings a new direction for the exploration of glass matrix.
Pr³⁺ singly doped SiO2-Na2O-Al2O3-LaF3 glass ceramics were fabricated as an inorganic color converter with wide color gamut for white light emitting diodes (wLEDs). Under 450 nm LED excitation, the simultaneous photo-luminescence (PL) emissions of green at 502 nm due to the Pr³⁺:³P1→³H4 transition and red at 613 and 643nm due to Pr³⁺:³P0→³H6 and ³P0→³F2, respectively, were observed. Before heat treatment, the PL intensity of the green and red emissions were limited relative to that of the blue electroluminescence (EL), due to the high transparency of the glass. This was highly improved by the crystallization of the glass with heat treatment. PrF3 concentration and heat treatment conditions such as temperature and duration time were varied to adjust the relative intensity of blue (EL), green and red (PL). The formation of LaF3 crystals within the glass ceramic and their effect on the visible spectra are discussed. The glass ceramics were mounted on top of a blue LED to fabricate a wLED, and demonstrate its practical feasibility, with a wide color gamut of up to 120 % of the NTSC.
In this study, we developed a highly efficient photoluminescent glass from the design of a short–medium range structure and the photoluminescence (PL) of a fluoroborate glass. We investigated PL and the structures of BaMgBO3F ceramics and the B2O3-added composition of glasses and glass-ceramics. The glass showed higher quantum yield (QY) than ceramic samples, i.e., the QY was 95 % for glass and 51 % for ceramics, by a 395 nm excitation. The glass can contain a large amount of emission centers with small concentration quenching, and 15 % Eu-doped glass exhibited higher PL intensity and QY than commercial Y2O3:Eu³⁺ phosphor. The origin of a high QY and small concentration quenching were investigated by the structural analysis. The glass structure was investigated using ¹⁹F- and ¹¹B-magic-angle spinning nuclear magnetic resonance, extended X-ray absorption fine structure of Ba K-edge, and high-energy X-ray diffraction. Moreover, the glass structure was simulated by molecular dynamics. It was found that the glass had a structural similarity with BaMgBO3F crystal in the short-range order of B and Ba. The glass had a clear selectivity that B preferred to bind to O and Ba preferred to bind to F. The glass also exhibited unique medium-range ordering. Two types of Ba–Ba displacements were observed, which could be attributed to in-plane and out-plane layered displacements of the corresponding crystal, with the stacking structure of oxide–fluoride layers indicated by the radial distribution. The glass showed anion segregation, also similar to the layer-stacking structure of BaMgBO3F. This made the low phonon sites coordinated with F compatible with the asymmetric sites derived from the oxide network segregation, resulting in high PL efficiency. The study results can contribute to the use of rare-earth ion-doped glasses in various applications such as laser and optical amplification, white light emitting diode (LED) lighting, and sensing technologies.
Solid state lighting, including phosphor converted light-emitting diodes (LEDs) and laser diodes (LDs), have released high demand to develop thermally stable phosphors. For this purpose, inorganic glass-ceramics (GCs) embedded with phosphor particles can act as competitive candidates. They are superior to traditional phosphors or resin/silica composites through successfully overcoming thermal aging and color temperature drifting problems and simultaneously maintaining high luminescent efficiencies. Inorganic GC phosphors can be classified into devitrified glass-ceramics, PiG (Phosphor-in-Glass) and sintered glass-ceramics. This review summarized the recent progress on LED/LD GC phosphors from the aspects of design principles, synthesis methods, microstructure-property relationships and their application studies. In addition, some challenging issues (e.g., crystallization behavior of luminous phase in glass, corrosion behavior of phosphor by glass matrix) are also discussed in detail. Significant issues of glass-ceramics packed LED/LD, such as luminescence efficiency, chromaticity, correlated color temperature and color gamut, are sorted out as well. Potential research directions are further suggested for not only developing new glass-ceramic phosphors but feeding upon various practical application.
A series of nanocomposites of recycled soda‐lime glass from a glass container and YAG:Ce³⁺ phosphor nanoparticles were fabricated by the two‐step low‐temperature co‐sintering technology. A transparent glass bottle from a commercial beverage was used as glass frit source and mixed with YAG:Ce³⁺ nanoparticles. Afterward, the powders were pressed to obtain pellets with phosphor concentrations in the range of 2.5 – 15 wt.%. The pellets were sintered at 800°C and 900°C. XRD analysis shows that YAG:Ce³⁺ nanoparticles are conserved even after sintering at 900°C. XRD analysis shows that YAG:Ce³⁺ nanoparticles are conserved even after sintering at 900°C. The emission spectra of the Ce³⁺ ions of YAG nanoparticles combined with the transmitted blue light exhibited color tuning related to the phosphor concentration and the sintering temperature. A tonality shift from cold‐white light towards yellowish‐green region was observed according the estimated CIE1931 chromaticity. Thus, recycled glass from a commercial glass container and YAG:Ce³⁺ nanoparticles PiGs can be an eco‐friendly and low‐cost alternative as color converters.
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Owing to the great thermal stability, phosphor-in-glass (PiG) is a promising color converter for the laser diode (LD) excitation based high-power white light-emitting LDs. Here, we reported the rapidly developed PiG plates using a facile microwave irradiation technique where the YAG:Ce³⁺ phosphor embedded with soda-lime silica glass. The effects of phosphor content and microwave irradiation energy were studied for investigating the optimal performance of PiG plate. To evaluate the practical applicability, the luminescence and thermal properties of the PiG plate was compared with the commercial YAG:Ce³⁺ single-crystal. The PiG plate and YAG:Ce³⁺ single-crystal individually combined with blue LD exhibited the white light with the CIE color coordinates of (0.3016, 0.3098) and (0.3254, 0.3555), respectively. The maximum surface temperature of the PiG plate was found to be about 96.1 °C, which is much lower than the YAG:Ce³⁺ single-crystal of 124 °C. The change in the CIE color coordinate of the PiG with aging time is smaller than that of YAG:Ce³⁺ single-crystal. This PiG plate might provide an important implication to overcome current limitation of LD driven solid state laser lighting.
SiO2–Na2O–Al2O3–LaF3 glasses doped with Eu²⁺ and Mn²⁺ were synthesized to fabricate an inorganic color converter for white LED. When Eu²⁺ was formed within the glass matrix, the obtained glasses showed cyan emission under 400 nm excitation upon heat treatment and the emission peak has been shifted with the crystallization. White emission has been successfully achieved with the introduction of Mn²⁺ which supplemented red emission. The glass ceramic has been mounted on a 400 nm UV-LED and successfully demonstrated its practical feasibility with color rendering index of 91.3. The effect of heat treatment and energy transfer between Eu²⁺ and Mn²⁺ has been discussed.
Phosphor-in-glass (PiG) is a mixture of a transparent glass and ceramic phosphors and has been recently commercialized for its various advantages as an inorganic color converter for white light emitting diodes (wLEDs). Since the successful demonstration of the wLED and its improved stability over the conventional phosphors in silicon or organic resins, extensive studies have been reported to improve its color conversion and resultant LED properties, such as luminescence efficacy, chromaticity, correlated color temperature and color gamut, as well as its long term stability. Various attempts have also been made to fabricate a PiG structure and to extend its applications. This study reviews the recent progress of PiG and discusses various approaches that have been proposed to overcome the technical issues related to PiG.
Silicate glasses with varying SiO 2 and Na 2 O contents were prepared and their viscous flow property at the elevated temperature was studied. When the glass powders were packed and sintered at 550 o C to examine their feasibility as a low sintering temperature glass frit, contrary to expectations, glasses with lower SiO 2 content than 60 mol% showed no vitrification after sintering. High temperature microscopy revealed the viscous flow change of the silicate glasses with varying temperature and duration time and also indicated that the viscous flow was limited at low SiO 2 content. X-ray diffraction (XRD) on the sintered samples and Raman spectroscopy were carried out to shed light on the compositional dependency of viscous flow of silicate glasses.
Novel dual valence Eu-doped phospho-alumino-silicate glass-ceramics containing orthorhombic Ba3AlO3PO4 nanocrystals were first fabricated by a traditional melt-quenching method and subsequent heat-treatment in an air atmosphere. Their structural and luminescent properties were systemically investigated by XRD, TEM analysis, and spectroscopic and fluorescence lifetime measurements. The incorporation of Eu³⁺ into Ba3AlO3PO4 crystallites and the reduction mechanism of Eu³⁺ to Eu²⁺ were also discussed based on the optical analyses. Simultaneously, perfect white light emission was obtained under 325 nm excitation. An improved anti-thermal quenching property was achieved resulting from the successful enrichment of Eu³⁺ and Eu²⁺ into Ba3AlO3PO4 crystallites, which was evidenced by active energy calculation. Our results indicate that these dual valence Eu-doped transparent Ba3AlO3PO4 glass-ceramics may have potential applications in W-LEDs.
A low sintering temperature glass based on the SiO2–P2O5–ZnO–B2O3–R2O (R=K and Na) system was studied as a matrix for embedding phosphors to fabricate color tunable white LEDs. The proposed system, which uses no heavy-metal elements and can be sintered at 500°C, incorporates thermally weak commercial phosphors such as CaAlSiN3:Eu2+ to produce phosphor-in-glasses (PiGs). Changing the mixing ratio of glass to phosphors affected the photo-luminescence spectra and color coordinates of the PiGs when mounted on a blue LED. The color rendering index (CRI) and color correlated temperature (CCT) of the LEDs were also varied with the mixing ratio, providing color tunable white LEDs. A high CRI, up to 93, as well as highly improved thermal stability were obtained, along with a low sintering temperature compared to other glass systems, suggesting the practical feasibility of the proposed system.
Ce³⁺: Y3Al5O12 (Ce-YAG) phosphors-in-glass (PiG), which serves as both luminescent convertor and encapsulating material in the remote white light-emitting diodes (LEDs), has become a promising research field. However, the challenges in processing and mechanical strength still remain due to its submillimeter thickness. Herein, a novel transparent Ce-YAG PiG thick film was coated on a common glass substrate through conventional screen printing process and subsequent heat treatment. The introduced commercial Ce-YAG phosphors almost kept intact in a lead-free glass matrix. The microstructures and luminescent properties of as-prepared samples were investigated systematically. White LED device was also fabricated via mounting the optimal sample on the InGaN blue-emitting chips, which yielded bright white light with considerable luminous efficiency and color quality. The resulting screen-printed Ce-YAG PiG thick film will be a promising candidate for applications in the high-power remote white LEDs.
Duo to the unique luminescent property, thermal conductivity and chemical stability, phosphors/glass composite (Phosphor-in-Glass, PiG) has a huge market application prospect as an alternative to silicon-based phosphor converter for conventional white LEDs, as well as a solution to the heat emission, luminous efficiency, quality, glare, lifetime and other technical problems at the same time. Herein, some key scientific topics in terms of PiG materials were analyzed, such as luminescence properties, transparency, mechanical strength, and mass production; the targeted optimization measures were also comprehensively summarized, including preparation methods (tabletting sintering, melt quenching, and film sintering), material composition design, and the structure optimization of phosphor layers. Generally, this review presents the most recent advances of excellent performance PiG materials, and also prospects their research trend.
Fluorescent glass frits were prepared and used to synthesize phosphor-in-fluorescent glass composites (PiFGs) to realize stable white light emitting diodes with high color-rendering properties. Commercial red, green, and blue phosphors were co-sintered and red phosphors were partially replaced by Eu3+ in glass frits. Phosphor-in-glass composites were placed on UV-light emitting diodes (UV-LEDs) to generate white light. Pure white light with a luminous efficacy=58.4 lm/W, general color rendering index Ra=87 and special color rendering index for strong red R9=73 was realized with glass frits containing 7 mol% Eu2O3 and RGB ratio of 35:20:15. Luminous efficacy, Ra and R9 increased as red phosphors were replaced by red-fluorescent glass frits.
To relieve the issues of high correlated color temperature and low color rendering index, it is urgent to develop an inorganic color converter materials with both red- and yellow-emission to replace the conventional organic resin/silicon-based color converter and acquire warm white light-emitting diodes (WLEDs). In our work, transparent glass–ceramics (GCs) containing Ce³⁺:Y3Al5O12 (Ce³⁺:YAG) yellow phosphors and Eu³⁺ ions are successfully fabricated by using low temperature co-sintering technique. And then the microstructure and luminescence properties of the GC are investigated in detail. Importantly, the impact of Ce³⁺:YAG phosphors concentration, Eu³⁺ ions concentration, co-sintering time and the GC thickness on optical performances are also systematically demonstrated. Impressively, the as-fabricated samples exhibit an efficient red emission at 611 nm owing to the ⁵D0→⁷F2 transition of Eu³⁺. Subsequently, the temperature-dependent luminescence and thermal quenching is also investigated. Finally, the constructed WLEDs show an optimal luminous efficacy of 120.85 lm/W, a color rendering index of 70.2 and a correlated color temperature of 5267 K. All the results indicate that the as-fabricated GC would have potential practical applications in high-power WLEDs.
Phosphor-in-glass (PiG) thick film was fabricated on a borosilicate glass substrate using a conventional screen printing method and employing phosphosilicate glass to allow low-temperature sintering. The vehicle content and sintering temperature were optimized to form a thick film with a thickness of ~50 μm. Commercial yellow (Y3Al5O12:Ce3+) and red (CaAlSiN3:Eu2+) phosphors were successfully incorporated within the glass matrix and then sintered at 550°C. Color-tunable white LEDs were achieved using the PiG thick films as a color converter by varying the glass to phosphor (GtP) ratio. The high luminous efficacy of up to ~120 lm/W and high color rendering index of up to 89 in combination with the thermal quenching property prove the practical feasibility of the PiG thick films for high-power/high-brightness LED applications.
This chapter discusses how the aluminophosphate glass system was developed with mixed alkali effect (MAE) method consideration by adding Li+ and Na+ with the relative cations concentration ratio equal to 1:1 to obtain lower characteristic temperatures. The glass substrate with a greater WR provides an excellent operating temperature opening for the glass-ceramic-phosphor preparation process without crystallization. The high transmittance of matrix glasses is beneficial to GCP performance for LED lighting and optical applications. The surfaces between glass substrate and phosphor-containing layer contained trace of precipitation of BiPO4. The slightly accumulation of BiPO4 crystals under phosphors could enhance the difficulty for further deposition of phosphor in glass. The cross-sectional and the color mapping images indicated that the YAG powders were well distributed in aluminophosphate surface layer and no interaction between glass substrate and phosphor-containing thin layer were observed.
In this study, we introduce a low-melting-point (MP) glass ceramic (GlaC) material which can be used to fabricate a phosphor-in-glass (PiG) with Y3Al5O12:Ce³⁺ (YAG) phosphor for the realization of high-power white-light-emitting diodes (WLEDs). PiG using a low-MP Sn-P-rich GlaC material, with simple fabrication at 230 °C, can address the drawbacks of the phosphor thermal degradation of currently developed PiGs with a high MP of more than 400 °C, and the yellowing of commercialized phosphor-in-silicon binder (PiSB) materials. In addition, the low-MP PiG can serve as a heat sink due to its good thermal conductivity and good stability compared to those of commercialized PiSB materials. The optical properties of a low-MP PiG-based WLED are a luminous efficacy (LE) of 118 lm W⁻¹, an external quantum efficiency (EQE) of 0.33 and a color-rendering index (CRI) of 68 at 4275 K at an applied current of 350 mA. The simply fabricated and stable PiG-based WLED using the low-MP GlaC material will be a competitive candidate in the WLED lighting market.
Currently, phosphor-in-glass (PiG) approach draws great attention because of its excellent thermal resistance and facile process in w-LED fabrication. However, the absence of red emissive component results in poor chromaticity quality, which greatly restricts its application in the high-quality indoor lighting. In the present work, a transparent garnet-based PiG was successfully prepared by introducing the Y3Al4.5Ga0.5O12:Ce³⁺ (YAGG) green phosphor into TeO2-based glass matrix, and we demonstrated the possibility offered by the screen-printing technique for warm w-LED applications by coupling the PiG plate stacked with a red phosphor coating on commercial InGaN LED. The microstructures and luminescent properties of them were investigated in detail. After simply varying the red phosphor concentration as well as the YAGG PiG thickness, a facile chromaticity tuning for the thus-fabricated LED was achieved in the range changing from cool white to warm white. Moreover, this developed luminescent material presented an excellent heat-resistance performance. Hopefully, the red phosphor coated PiG color converter is applicable in the long-lifetime high-power color-tunable w-LEDs.
Currently, phosphor-in-glass (PiG) approach draws great attention because of its excellent thermal resistance and facile process in WLED fabrication. However, the red light deficiency results in high correlated color temperature (CCT) and low color rendering index (CRI) in white light-emitting diode (WLED). Herein, a new LuAG:Ce3+ phosphor-in-glass (Lu-PiG) combining with the CaAlSiN3:Eu2+ red phosphor layer was synthesized by the low temperature co-sintering and screen-printing techniques, which was experimentally demonstrated to replace the conventional polymer-based phosphor converter and realized the chromaticity tuning for LuAG:Ce3+ phosphor with WLED. The Lu-PiG constructed WLED exhibited excellent thermal stability, but it still showed a typical cold white light resulting from the absence of red light component. Therefore, a stacking geometric configuration by screen-printing a red phosphor layer on the Lu-PiG substrate (R&Lu-PiG) was designed to solve red deficiency problem. The R&Lu-PiG color converter showed an excellent thermal stability with only 8.2 % emission loss compared to the Lu-PiG when elevating temperature from 303 K to 433 K. By adjusting the CaAlSiN3:Eu2+ phosphor content in the layer, we obtained a high-performance warm WLED with a luminous efficacy of 102.1 lm/W, a CCT of 3410 K and a CRI of 76.5 under 20 mA current driving. Thus, it is expected that this developed R&Lu-PiG color converters could have large potential applications in high-power warm WLED.
A pivotal step in providing a better fluorescent material that has high luminous efficacy and excellent thermal stability is to utilize inexpensive phosphors for white light-emitting diodes (W-LEDs). Herein, we demonstrate a feasible tape-casting technique for creating phosphor thick films that consist of Ce:YAG phosphor embedded in relatively low melting point glass frits on an ultrathin glass substrate with controllable film thickness. The glass matrix has ideal densification and interfaces with the glass substrate at a relatively low temperature of 580 °C. Subsequently, the structure and optical properties of the phosphor layer are investigated. In addition, the effect of the phosphor concentration, thick film thickness and location (top or bottom) of the phosphor layer on the photoluminescence properties and chromaticity are also discussed with respect to use in W-LEDs. Significantly, this promising structure has excellent thermal stability and the potential to overcome current limitations of phosphors in high-power W-LEDs. Finally, a high-performance W-LED based on the planar phosphor glass exhibits a luminous efficiency of 108.45 lm·W−1, a correlated color temperature of 5408 K and a color rendering index of 76.
Phosphor in glasses (PiGs) were fabricated for color tunable white LEDs using glass of the SiO2-B2O3-ZnO-Na2O system, which can be sintered at 550 °C. CaAlSiN3:Eu2 + (CASN:Eu2 +) red phosphor was added without its thermal degradation, and a mixture with Y3Al5O12:Ce3 + (YAG:Ce3 +) yellow phosphor demonstrated color tunable white LEDs when mounted on a blue LED. Variation of the glass to phosphor and phosphor to phosphor mixing ratio achieved a highly improved color rendering index (CRI), of up to 93. Thermal quenching property was also improved, reaching 98% of its original intensity even at 200 °C; the value depended on the phosphor content. Thermal conductivity values elucidate the improvement.
Ce:YAG polycrystalline ceramics with different SiO2 content were successfully prepared by a single-step melt-quenching method. The characterization of the resulting polycrystalline ceramics was accomplished by using X-ray powder diffraction, field emission scanning electronic microscopy and energy dispersive X-ray spectroscopy. Then, the optical properties were investigated using a fluorescence spectrometer. It is found that the glass matrix becomes a glassy state more easily, the photoluminescence excitation (PLE) and PL intensity decrease obviously and crystallization of YAG is difficult to generate as the SiO2 content increases. What's more, the intensity of the blue LED decreases and that of the yellow emission band instead increases and saturates at a SiO2 content of 32 mol% in the electroluminescent (EL) spectra. Afterwards, the photoelectric performance was studied by an LED spectrometer. As a consequence, the constructed polycrystalline ceramic based WLED exhibits a high luminous efficiency of 74.44 lm W-1, and a correlated color temperature of 5351 K as well as a color rendering index of 75.91, which reveals the prominent feasibility of the present polycrystalline ceramic material in WLED applications.
SiO2–Na2O–Al2O3–LaF3 glasses were doped with various rare earth ions to find the proper active ions for blue LED (λ = 455 nm) color conversion. Based on photo-luminescence (PL) spectra, a combination of Dy3+ and Ho3+ was selected and their visible spectroscopic properties were investigated for possible candidate of white color conversion of a blue LED. Concentrations of Dy3+ and Ho3+ were varied to find the proper combination, and 2 mol% DyF3 and 1 mol% HoF3 co-doped glass showed reasonable visible emissions. When the glasses were heat treated, emission intensities from both ions were clearly increased by the formation of LaF3 nano-crystals, which were identified by X-ray diffraction and TEM analyses. Emission peak at ~ 525 nm newly appeared due to nano-crystal formation and the related local phonon energy change nearby Dy3 + ion. Energy transfer between Dy3 + and Ho3 + was also observed and discussed. Photo-luminescence excitation (PLE) spectra were measured and also discussed.
To alleviate the issues of low thermal stability and high correlated color temperature, exploring an inorganic color converter with both yellow- and red- emitting to replace the conventional resin/silicone-based phosphor converter for high-power warm white light-emitting diodes is highly desired so far. In this study, a series of garnet-based Li6CaLa2-2xEu2xSb2O12 (x=0.1~1.0) red phosphors have been successfully synthesized by a conventional high-temperature solid-state method. The microstructure and luminescence properties were systematically investigated by X-ray diffraction, emission/excitation spectra, luminescence lifetimes and temperature-dependent decays. The as-synthesized phosphors exhibited highly efficient red luminescence at 611 nm corresponding to the Eu3+ 5D0-7F2 electric dipole transition, and the luminescence monotonously enhanced as the Eu3+ content increasing to 100 mol%. The absence of concentration quenching was ascribed to the large Eu3+-Eu3+ distance (7.048~7.105 Å) and subsequently the hampering of the unwanted energy migration among them in the Li6CaLa2Sb2O12 crystalline lattice. Impressively, the Li6CaLaEuSb2O12 phosphor showed excellent thermal stability with only 9.7% loss when the recording temperature was raised from 293 K to 553 K. To evaluate the suitability of Li6CaLa2Sb2O12:Eu3+ as red converter, both the garnet-based Y3Al5O12:Ce3+ yellow phosphors and Li6CaLa2Sb2O12:Eu3+ red ones co-doped glass ceramics have been successfully fabricated by a low-temperature co-sintering technique. Importantly, the adverse energy transfers between Ce3+ and Eu3+ are efficiently suppressed due to the spatial separation of Ce3+ in Y3Al5O12 and Eu3+ in Li6CaLa2Sb2O12 crystal lattice. As a consequence, the quantum yield of the glass ceramic reached as high as 89.3%, and the constructed white light-emitting diode exhibited an optimal luminous efficacy of 101 lm/W, a correlated color temperature of 5449 K and a color rendering index of 73.7. It is expected that the developed Li6CaLa2-2xEu2xSb2O12 red phosphors and the related glass ceramics should have potential applications in the high-power warm white light-emitting diodes.
SiO2–Na2O–Al2O3–LaF3 glasses doped with Eu2+ and Eu3+ were synthesized to realize an inorganic color converter for white LED using 400 nm UV LED. Among various rare earth ions, Eu2+ and Eu3+ showed prominent emission under 400 nm LED excitation. Carbon and EuF3 content were varied to control the ratio of Eu2+ and Eu3+ during the melting process. When the ratio of Eu2+ and Eu3+ within the glass matrix was properly controlled, color coordinates of the photoluminescence spectra could be adjusted to make white colors under 400 nm LED excitation. The emission intensity was increased with subsequent heat treatment which led to the formation of LaF3 nano-crystals. However, almost no conversion was observed when the glasses were actually mounted on UV-LED to make a white LED. Heavy crystallization of the oxyfluoride glasses was thus investigated to improve its scattering of the light source and color conversion efficiency, and its practical feasibility as an inorganic UV-LED color converter was demonstrated.
We demonstrate all-in-one-type organic light-emitting diodes (OLEDs) that are fabricated using a color converting plate as a substrate. The color converting plate is Pb-free phosphor-in-glass (PiG), which is prepared by mixing Y3Al5O12:Ce3+ (YAG:Ce3+) and SiO2–B2O3–RO (R = Ba, Zn) glass frit by sintering at 750 °C for 30 min. The maximum luminance, luminance efficiency, and power efficiency of blue OLEDs fabricated on commercial glass are measured as 10500 cd/m2, 10.18 cd/A, and 2.95 lm/W, respectively. The Commission Internationale de l'Eclairge (CIE) coordinates of blue OLEDs is (0.167, 0.325). Our obtained results show that the luminance value decreased as the PiG thickness increased, and the glass to phosphor (GTP) ratio decreased. The OLED devices fabricated on the PiG substrate (GTP ratio = 9:1, thickness: 150 μm) showed a maximum luminance, luminance efficiency, and power efficiency of 7600 cd/m2, 8.76 cd/A, and 2.85 lm/W, respectively. The CIE color coordinates changed to (0.286, 0.504) at 200 mA/cm2. These results proved that color coordination can be easily adjusted by varying the GTP ratio and the thickness of the PiG.
Phosphor-in-glasses (PiGs) with rare earth (RE) doped SiO2–B2O3–RO glasses were prepared by embedding YAG:Ce3+ as the yellow phosphor. Eu3+ and Pr3+ were used to dope the glass, varying their concentrations in order to provide red emissions for possible chromaticity-control of white-light emitting diodes (WLEDs). The glass-to-phosphor mixing ratio was also varied to find the proper combination for color-controlled white LEDs. PiGs with RE-doped glasses were sintered at 750 °C and polished to 250 μm in thickness for blue LED color conversion. The photoluminescence spectra of the PiGs were monitored after they were mounted on commercial blue LED chips. Variation of color coordination, color rendering index and correlated color temperature were observed due to red emissions from the doped RE-ions. The spectral contribution of Eu3+ and Pr3+ ions to white LEDs under 450 nm LED excitation was discussed. The spatial distribution of phosphors within the glass matrix, and their possible interaction, was inspected by SEM. The thermal quenching effect was also investigated.
A series of tunable emission phosphors Ca2PO4Cl:Ce3+, Tb3+ are synthesized by a high temperature solid-state method. The emitting color of Ca2PO4Cl:Ce3+, Tb3+ can be adjusted from blue to green with increasing the Tb3+ doping content. The energy transfer from Ce3+ to Tb3+ in Ca2PO4Cl has been validated, and proved to be a resonant type via a dipole–dipole interaction. The critical distance of energy transfer is calculated by the concentration quenching method, and about 1.77 nm. Ca2PO4Cl:Ce3+, Tb3+ has a broad excitation band in the near ultraviolet range, and produces green emission, therefore, it may have potential application as near ultraviolet convertible phosphor for white light emitting diodes.
Phosphor-in-glass (PiG) color converters for LED applications were fabricated with a mixture of phosphors, Y 3 Al 5 O 12 : Ce 3 + (yellow) and CaAlSiN 3 : Eu 2 + (red). The low sintering temperature (550°C) of SiO 2 – Na 2 O – RO ( R = Ba , Zn) glass powder enabled the inclusion of CaAlSiN 3 : Eu 2 + (red) phosphor which cannot be embedded with conventional glass powders for PiGs. By simply varying the mixing ratio of glass to phosphors as well as the ratio of yellow to red phosphors, the facile control of the CIE chromaticity coordinates and correlated color temperature of the LED following the Planckian locus has been achieved. Phosphors were well distributed within the glass matrix without noticeable reactions, preserving the enhanced thermal quenching property of the PiG compared to those with silicone resins, for LEDs.
We have developed a Ce:YAG (Y3Al5O12) glass-ceramic phosphor for the white LED. The glass-ceramic phosphor was obtained by a heat treatment of a Ce-doped SiO2-Al2O3-Y2O3 mother glass between 1200°C and 1500°C for the prescribed time of period. We confirmed that, by XRD measurements, only YAG crystal precipitated in the mother glass after the heat treatment. It was shown from SEM observation that the YAG crystals with a grain size of approximately 20mum were uniformly dispersed in the glass matrix. The yellow emission, around 540nm in wavelength, was observed from the glass-ceramic phosphor, when it was excited by a blue LED (465nm). The white light due to the mix of yellow and blue light was observed from the glass-ceramic plate with a thickness of 0.5mm. The YAG glass-ceramic phosphor showed a high-temperature resistance and a good performance in a damp heat test. Moreover, a higher thermal conductivity of 2.18 Wm-1K-1 and bending strength of 125MPa were observed compared with a conventional soda-lime glass or an epoxy resin. In addition, since the YAG glass-ceramic phosphor can be formed in a plate-like shape, there is no need to be sealed in resins for the fabrication of the LED devices. Therefore, it is expected that this newly developed glass-ceramic phosphor is a promising candidate for the realization of resin-free, high-temperature and high-humidity resistant, long-life white LED devices.
A phosphor-converted light-emitting diode was obtained with nearly ideal blue-to-white conversion loss of only 1%. This is achieved using internal reflection to steer phosphor emission away from lossy surfaces, a reflector material with high reflectivity, and a remotely located organic phosphor having (1) unity quantum efficiency (ηq), (2) homogeneous refractive index to minimize scattering, and (3) refractive index-matched to the encapsulation to eliminate total internal reflection. An inorganic composite phosphor is also reported with a nearly homogeneous refractive index to minimize diffuse scattering of emitted light, thereby maximizing the effective phosphor ηq and light extraction.
Roughened surfaces of light-emitting diodes (LEDs) provide substantial improvement in light extraction efficiency. By using the laser-lift-off technique followed by an anisotropic etching process to roughen the surface, an n-side-up GaN-based LED with a hexagonal “conelike” surface has been fabricated. The enhancement of the LED output power depends on the surface conditions. The output power of an optimally roughened surface LED shows a twofold to threefold increase compared to that of an LED before surface roughening. © 2004 American Institute of Physics.
Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.
The blue-light-excitation-type white light-emitting diode (LED) lamps are considered to be very suitable for lighting for art objects, shop window displays, and medical applications because they do not give infrared ray and ultraviolet ray. But their color rendering indices are needed to be improved for such applications. In this letter, the authors have fabricated white LED lamps with a broad range of color temperatures, and realized extrahigh color rendering index Ra values of 95–98 in them, using four oxynitride/nitride phosphors and a blue LED die. It means UV LED die is not always necessary for high color rendering white LED lamps. The luminous efficacies of white LED lamps are 28–35 lm / W , which are sufficiently high for extremely high color rendering white LED lamps.
In this letter, a yellow-emitting Sr 3 Si O 5: Ce 3+, Li + phosphor is reported. Through transitions of 5d→4f ( 2F7/2 and 2F5/2 ) in Ce 3+ , the phosphor showed a very broad and strong yellow emission under near ultraviolet (UV) or blue light excitation. The energy levels of Ce 3+ in Sr 3 Si O 5 were suggested from its absorption and excitation spectra. White light could be obtained by combining this phosphor with 460 or 405 nm light-emitting diodes (LEDs) [ (x,y)=(0.3086,0.3167) or (0.3173, 0.3103)]. Additionally, a yellow LED was fabricated using a near-UV LED ( 380 nm chip) with Sr 3 Si O 5: Ce 3+, Li + .
Solid-state lighting using light-emitting diodes (LEDs) has the potential to reduce energy consumption for lighting by 50% while revolutionizing the way we illuminate our homes, work places, and public spaces. Nevertheless, substantial technical challenges remain in order for solid-state lighting to significantly displace the well-developed conventional lighting technologies. We review the potential of LED solid-state lighting to meet the long-term cost goals.
The effect of mixing ratio, firing temperature and matrix glass composition on afterglow luminance property of SrAl2O4: Eu2+,Dy3+-glass composites were investigated. As a result, the brightness showed a maximum at 35 mass % of the mixing ratio of the phosphor for the glass and 780 degrees C of the firing temperature. And it was increased with decreasing the Na2O content of the matrix glass. From the backscattered electron and the EDX analysis, it is thought that the intermediate layers generated between the phosphors and the Na2O-poor matrix glass work as antireflective and the phosphor particles in the composite emit phosphorescent light more efficiently. As higher the basicity parameter, B, the intermediate layer was clearer, which means that the reactivity at the phosphor/glass boundaries was lower, and the narrow reaction layers was formed. 2010 The Ceramic Society of Japan. All rights reserved.
High bright and white light emitting diodes(LEDs) were fabricated. White LEDs are the fourth color made for commercial use following blue, green and red. White LEDs typically have the efficacy of 10 lm/W and the color temperature of 3000K-10000K. This new technology was achieved by combining blue InGaN LED and YAG phosphor. Compared with incandescent lamps, advantages such as wide color variation, life beyond 10000hr, no burn-out, reduced sensitivity to variation and little heat generation are expected.
An optimized packaging configuration for high-power white-light-emitting diode (LED) lamps that employs a diffuse reflector cup, a large separation between the primary emitter (the LED chip) and the wavelength converter (the phosphor) and a hemispherically shaped encapsulation is presented. Ray tracing simulations for this configuration show that the phosphor efficiency can be enhanced by up to 50% over conventional packages. Dichromatic LED lamps with phosphor layers on the top of a diffuse reflector cup were fabricated and studied experimentally. The experimental enhancement of phosphor efficiency is 15.4% for blue-pumped yellow phosphor and 27% for ultraviolet-pumped blue phosphor. Those improvements are attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant.
We have synthesized a Eu2+-activated Sr2SiO4 yellow phosphor and investigated an attempt to develop white light-emitting diodes (LEDs) by combining it with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr2SiO4:Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that GaN (400-nm chip)-based Sr2SiO4:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460-nm chip)-based YAG:Ce. © 2003 American Institute of Physics.
Even though light-emitting diodes (LEDs) may have a very long life, poorly designed LED lighting systems can experience a short life. Because heat at the p-n-junction is one of the main factors that affect the life of the LED, by knowing the relationship between life and heat, LED system manufacturers can design and build long-lasting systems. In this study, several white LEDs from the same manufacturer were subjected to life tests at different ambient temperatures. The exponential decay of light output as a function of time provided a convenient method to rapidly estimate life by data extrapolation. The life of these LEDs decreases in an exponential manner with increasing temperature. In a second experiment, several high-power white LEDs from different manufacturers were life-tested under similar conditions. Results show that the different products have significantly different life values.
Phosphor conversion of light-emitting diode light for white light
sources and some monochrome applications requires particular phosphor
properties and has to take into account specific issues if aimed at
high-power output. Limitations and solutions will be discussed, giving
special considerations to drive and temperature dependencies.
Efficiencies of 32 lm/W for white with good color rendering at 4600 K
and 35 lm/W for green (535 nm) have been demonstrated