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Y 2 CaAlGe(AlO 4 ) 3 :Ce and Y 2 MgAlGe(AlO 4 ) 3 :Ce garnet phosphors for white LEDs

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Abstract

New phosphors with the compositions Y2CaAlGe(AlO4)3:Ce and Y2MgAlGe(AlO4)3:Ce were obtained by co-precipitation technique. Their structural, morphological and luminescence properties were investigated. The 2 shift observed in XRD patterns was attributed to the substitution of Y³⁺ and Al³⁺ ions by Ca²⁺ (Mg²⁺) and Ge⁴⁺ ions, respectively. It was shown that the composition of the new polycrystalline compounds is uniform. Both new phosphors exhibit a broad luminescence band, as usual for the Ce³⁺ ion emission in garnets. A shift of the band was observed and attributed to the different crystal field experienced by the Ce³⁺ ions in inequivalent sites in the complex garnets.

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... The aluminum− oxygen octahedron and the aluminum−oxygen tetrahedron are partly substituted by magnesium−oxygen octahedron and silicon−oxygen tetrahedron to form the Y 3 MgSiAl 3 O 12 :Ce 3+ compound, similar to other cosubstitution systems we investigated previously. 27,28 Because of the ion size and charge compensation, the crystal structure and the neutrality are maintained. Similarly, the substitution of Y 3+ by Ce 3+ ions, due to the same valence (+3) and similar ionic radius (CN = 8, R Ce 3+ = 1.143 ...
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We describe the basic illumination characteristics of lighting source using 10 cd-class InGaN-based white LED (an efficacy of 15 lm/W) under a driving condition of AC 100 V. 697 white LEDs with series connections were arrayed on a glass epoxy substrate and were driven by adjusting a current of less than 20 mA. The temperature dependence of both the emission spectrum and intensity was measured. The white LED array indicates two distinct electroluminescence peaks at 465 and 555 nm at room temperature, which are related to the radiative recombinations from the InGaN MQW blue LED and from the YAG : Ce phosphor, respectively. We have obtained a maximum luminous intensity of about 30 000 lx and a maximum luminance of 95 000 cd/m2 from the LED array.
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Long life, on the order of 50,000–100,000 h, is one of the key features of light-emitting diodes (LEDs) that has attracted the lighting community to this technology. White LEDs have yet to demonstrate this capability. The goal of the study described in this manuscript was to understand what affects the long-term performance of white LEDs. Different types of LEDs have different degradation mechanisms. As a starting point, this study considered a commonly available commercial package, the 5 mm epoxy-encapsulated phosphor-converted (YAG:Ce) white LED. Based on past studies, it was hypothesized that junction heat and the amount of short-wavelength emission would influence the degradation rate of 5 mm type white LEDs, mainly due to yellowing of the epoxy encapsulant. Two groups of white LEDs were life-tested. The LEDs in one group had similar junction temperatures but different amplitudes for the short-wavelength radiation, and the LEDs in the second group had similar amplitudes for the short-wavelength radiation but different junction temperatures. Experimental results showed that the degradation rate depends on both the junction temperature and the amplitude of short-wavelength radiation. However, the temperature effect was much greater than the short-wavelength amplitude effect. Furthermore, the phosphor medium surrounding the die behaves like a lambertian scatterer. As a result, some portion of the light circulates between the phosphor layer and the reflector cup, potentially increasing the epoxy-yellowing issue. To validate this theory, a second experiment was conducted with LEDs that had the phosphor layer both close to the die and further away. The results showed that the LEDs with the phosphor layer away from the die degraded at a slower rate.
Article
More than a century after the introduction of incandescent lighting and half a century after the introduction of fluorescent lighting, solid-state light sources are revolutionizing an increasing number of applications. Whereas the efficiency of conventional incandescent and fluorescent lights is limited by fundamental factors that cannot be overcome, the efficiency of solid-state sources is limited only by human creativity and imagination. The high efficiency of solid-state sources already provides energy savings and environmental benefits in a number of applications. However, solid-state sources also offer controllability of their spectral power distribution, spatial distribution, color temperature, temporal modulation, and polarization properties. Such “smart” light sources can adjust to specific environments and requirements, a property that could result in tremendous benefits in lighting, automobiles, transportation, communication, imaging, agriculture, and medicine.
Glass ceramics for solid state lighting
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