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The effect of binary glass composition on the Eu-ions luminescence properties
... Fig. 2(a) shows the optical transmission spectra obtained for the various glasses under consideration. The Eu glass exhibits the dip in the transmission spectrum around 393 nm due to 7 F 0 -5 L 6 transition of Eu 3+ ions, 16,17 while the host absorption edge characterizes the decreased transmission toward shorter wavelengths. 9 It is observed for the EuND1 glass that a decreased transmission developed around 320 nm while the glass appears to have the transmission edge shifted towards shorter wavelengths. ...
... 18,19 The results resemble the recently reported for the glasses melted with Eu 2 O 3 and MWCNTs in our group, 20 however the current spectra are achieved with ten times lower carbon (C ND ) loadings. Similar evolution in transmission spectra were also reported by Tratsiak et al. 16 and Liang et al. 19 following the conversion from Eu 3+ to Eu 2+ in silicate and borophosphate glasses, respectively. The development of the transmission in Fig. 2(a) decreasing with the increase in ND content is consistent with an increase in Eu 2+ concentration up to the EuND4 glass. ...
... Shown in Fig. 4 are emission spectra obtained for the glasses under the excitation wavelength of 320 nm in accord with the Eu 2+ absorption feature in Fig. 3. The presence of Eu 2+ is evidenced for the EuND1-4 glasses by the broad 5d -4f emission band 16,18,24 with maximum around 450 nm which is absent for the Eu glass. However, a saturation in the blue emission from Eu 2+ is observed after 1.0 mol% ND. ...
The role of nanodiamond as reductant and modifier of the optical properties of Eu-doped phosphate glasses toward photonic applications is scrutinized via optical transmission, photoluminescence spectroscopy, Raman scattering and calorimetry.
... The conversion of Eu 3+ to Eu 2+ in glasses has been a topic of interest in photonics during the past decades given that the luminescence switches from red to blue with the change in the electronic configuration of the europium ions from 4f 6 to 4f 7 [1][2][3][4][5][6][7][8]. Thus, the glasses have been attractive in the context of light-emitting devices (LEDs), phosphors and sensor applications. ...
... The europium doping of glasses is typically realized in the Eu 3+ state, and thereafter some post-treatment under strong reducing atmosphere [1,6,7], or suitable radiation [4,8], is applied to obtain the blue-emitting Eu 2+ ions. However, having a reducing agent together with Eu 2 O 3 alongside batch materials for a straightforward procedure presents a convenient route for material synthesis [11]. ...
... In Fig. 1 (a), the transmission spectra recorded for the 0.3-1MWCNT glasses is presented alongside the Eu glass (no MWCNTs added) as reference. The Eu glass shows the feature in the transmission spectrum around 393 nm due to 7 F 0 → 5 L 6 transition Eu 3+ ions [7,14], while the host absorption edge characterizes the decreased transmission toward shorter wavelengths [12]. It is observed for the 0.3MWCNT-Eu glass that a decreased transmission developed around 320 nm. ...
Glasses of BaO:P2O5 composition were melted with fixed Eu2O3 content and varying amounts of multi-wall carbon nanotubes (MWCNTs) for a spectroscopic and calorimetric study focusing on luminescent properties of interest to light-emitting devices. The optical transmission data indicated favorable Eu3+ → Eu2+ reduction with MWCNTs up to 1.0 wt% as judged by the 4f7 → 4f65d transitions of Eu2+ ions around 320 nm. A small amount of MWCNTs at 0.3 wt% lead to an improved Eu3+ luminescence under 320 nm relative to the Eu3+-doped reference likely due to a Eu2+ → Eu3+ energy transfer. On the other hand, the most intense emission around 450 nm corresponding to 4f65d → 4f7 radiative relaxation in Eu2+ was obtained for a glass melted with 0.7 wt% MWCNTs. Concentration quenching and optical band gap reduction are suggested to cause the decreased 450 nm band emission in the glass melted with 1.0 wt% MWCNTs. The glasses presented concomitant luminescence due to remaining Eu3+ ions, and the resulting emitted light under excitation at 320 nm was characterized by CIE diagram. Further, Raman spectroscopy was employed for a structural characterization, which was ultimately correlated with the thermal properties measured by differential scanning calorimetry.
... (3) Eu 2+ ions, a broad absorption band $320 nm (3.9 eV), 4f 7 ! 4f 6 5d 1 [20] ; (4) Cu 2+ ions in EuDyCu glass, with a broad band centred at $900 nm (1.38 eV), a solid green line (Figure 1c), attributed ...
... Therefore, in the proposed notation form, the assessed strength of the blue band yields the following inequality: Continuing with the PL excitation analysis, the comparison of the excitation spectra obtained by monitoring Eu 3+ emission at 612 nm provides strong evidence of the well known Dy 3+ !Eu 3+ ET, [12,13,25] giving rise to the Dy 3+ 350 nm excitation peak (Table 3) in all four glasses in Figure 2 (solid red line in each panel). The most prominent excitation band in the Eu 3+ transition, [13] was located at $362 nm ( [20] The most prominent excitation band in the Eu 3+ transition [13] is located at $362 nm (Table 2). Therefore, exploration of the 612 I s 250 = 612 I s 362 intensity ratios across the glass samples attempted to ascertain the relative quantification of CTB strength. ...
A thorough analysis of glasses containing Eu2O3 and Dy2O3, or Eu2O3, Dy2O3 and CuO melted together with nanodiamond powder was pursued based on measurements of optical absorption, photoluminescence (PL) emission and excitation spectra, and colorimetry. Nanodiamond facilitated the stabilization of Cu+ and Eu2+ ions with blue‐emitting character, which along with yellow‐emitting Dy3+ and red‐emitting Eu3+ lead to the white‐light emitting glasses. Novel intensity notations implemented in intensity‐based spectral ratios, and difference intensity correlation analysis were proposed for the assessment of PL properties. The chromaticity and corelated color temperature (CCT) of the emission were ultimately investigated as a two‐parametric problem based on: (i) the different ionic components; and (ii) the various excitation wavelengths employed. The optical analysis approach adds to the characterization methods to further fundamental understanding and provide helpful analytical tools for designing materials for tunable white‐light emitting devices.
... This area can be imagined as boundary crust or buffer area between the glass matrix and the particle. The Eu 2+ PL spectrum measured in the BaO-CaO·2SiO 2 :Eu(1 at.%) glass systems [35] was spread over approximately 400-600 nm region centered at about 450-500 nm (depended on the glass composition). ...
... The sample 5 exhibits Eu 2+ spectrum typical for glass (see Fig. 9). The spectrum measured in CaO·2SiO 2 :Eu(1 at.%) glass [35] is shown in contrast as well. It is not excluded that, some signals may come from the BaI 2 particles, however, strongly overlapped with the dominating glass ones. ...
Present paper reports an approach to BaI2:Eu²⁺ glass ceramic fabrication from a powder route. The structural, morphological, luminescent and paramagnetic properties of the materials synthesized this way have been investigated. X-ray diffraction analysis made evidence for the glass ceramics containing BaI2·2H2O and BaI2 inclusions when 50 wt.% of the starting iodide powder had been used in the synthesis process. According to scanning electron microscopy, only two samples demonstrated presence of ceramics particles inside: those with initial mix of 25 and 50 wt.% of the BaI2:Eu²⁺. Photoluminescence spectra could be measured only in these samples. They were multicomponent as compared to the single band spectrum observed in the BaI2:Eu²⁺ powder. Altogether this indicates europium distribution over several places with different environments in the materials. BaI2 dissolution in the glass matrix is confirmed further by electron paramagnetic resonance measurements. They have shown that the Eu²⁺ ions predominantly stay in the glass avoiding ceramic grains. Only negligibly small amount presumably occupies the ceramic part in the sample with the initial 50 wt.% part of the BaI2 powder. The Eu²⁺ → Eu³⁺ charge transformation under 442 nm laser light irradiation has been observed in the glass ceramics as well.
... [18][19][20][21][22] Usually, the 5 D 0 -7 F 2 transition intensity is enhanced with respect to the following: (i) the local glass network structure, (ii) the RE ion concentration and (iii) the MNP concentration along with the temperature treatment schedule. 2,3,[23][24][25] Because of the weak features, most studies related to Eu 3+ -emission properties do not concentrate on the 5 D 0 -7 F 4 transition. Nevertheless, the significant role of the dominant emission intensity of the 5 D 0 -7 F 4 transition has not been explored to date. ...
... In literature, usually the enhancement in the intensity of the 5 D 0 -7 F 2 transition of Eu 3+ is observed with respect to the glass composition, the RE ion concentration and the MNP concentration along with the temperature treatment. 2,3,[23][24][25] The intensity enhancement of the 5 D 0 -7 F 4 transition did not provide an explanation for most investigations of the Eu 3+ -containing glasses because the features were too weak. 2,3,16,24 In the present investigation we observed an abnormal intensity enhancement when the gold NPs were embedded in the glass composition, which might have been linked with the nonlinear intensity enhancement of the 5 D 0 -7 F 4 transition. ...
Alkali borate glasses activated with trivalent europium ions and rooted with gold (Au) nanoparticles (NPs) were synthesised through a melt quenching process involving a selective thermochemical reduction and their applicability as photonic materials was assessed in detail. Non-linear optical (NLO) measurements were performed using a Z-scan approach in the wavelength range of 700-1000 nm. The open aperture Z-scan signatures for the Eu 3+-containing glasses embedded with and without the Au NPs established a reverse saturable absorption (RSA) at all of the studied wavelengths ascribed to the two-photon absorption (2PA). Surprisingly, the nonlinear optical absorption switched to a saturable absorption (SA) with an increase in the concentration of AuCl 3. With the incorporation of the Au NPs, the UV excited photoluminescence (PL) intensity of the Eu 3+-doped glasses increased first as a consequence of the local field enhancement by the Au NPs, and subsequently decreased at a higher concentration of AuCl 3 due to the reverse energy transfer from the Eu 3+ ion to the Au 0 NPs. The electronic polarization effect of the host glass enhanced the 5 D 0-7 F 4 transition intensity on the incorporation of the gold NPs owing to the gold NP-embedded glasses showing a deep-red emission. The NLO and PL studies suggested that the investigated glasses containing a 0.01 mol% of AuCl 3 is practically appropriate for photonic applications.
... Usually, the 5 D 0 → 7 F 2 transition intensity enhances with respect to the following: (i) local glass network structure, (ii) RE ion concentration and (iii) MNPs concentration along with the temperature treatment schedule. 2,3,[23][24][25] Because of the weak features, most of the studies related to Eu 3+ -emission properties do not concentrate on the 5 D 0 → 7 F 4 transition. ...
... In literature, usually the enhancement in the intensity of the 5 D 0 → 7 F 2 transition of Eu 3+ is observed with respect to the glass composition, with respect to the RE ions concentration and with respect to MNPs concentration along with the temperature treatment. 2,3,[23][24][25] The intensity enhancement of 5 D 0 → 7 F 4 transition does not explain in most of the investigations of Eu 3+ containing glasses because the features are so weak. 2,3,16,24 In the present investigation we have observed abnormal intensity enhancement when the gold NPs are embedded in the glass composition, which might be linked with the nonlinear intensity enhancement of 5 D 0 → 7 F 4 transition. ...
Alkali borate glasses activated with trivalent europium ions and rooted with gold (Au) nanoparticles (NPs) are synthesised through the process of the melt quenching involving the selective thermochemical reduction and their applicability as photonic materials have been assessed in detail. The non-linear optical (NLO) measurements have been performed using Z-scan approach in the wavelength range of 700–1000 nm. The open aperture Z–scan signatures for Eu3+ containing glasses embedded with and without Au NPs established a reverse saturable absorption (RSA) at all the studied wavelengths ascribed to two-photon absorption (2PA). Surprisingly, the nonlinear optical absorption switches to saturable absorption (SA) with increasing the concentration of AuCl3. With the incorporation of Au NPs, the UV excited photoluminescence (PL) intensity of Eu3+ doped glasses increased first as a consequence of the local field enhancement by Au NPs, and subsequently decreased at higher concentration of AuCl3 due to the reverse energy transfers from Eu3+ ion to Au0 NPs. The electronic polarization effect of host glass enhanced the 5D0→7F4 transition intensity on the incorporation of gold NPs owing to which, the gold NPs embedded glasses show a deep-red emission. The NLO and PL studies suggested that the investigated glasses containing 0.01 mol % of AuCl3 is practically appropriate for photonic applications.
... Both charge states of europium, Eu 2+ and Eu 3+ , emit under UV irradiation in the visible spectral region. The exact luminescence efficiency and spectral region of the europium activator is dependent on the surrounding environment and on the Eu 2+ /Eu 3+ ratio [9,10]. The Eu 2+ dopant particularly emits in the blue region [11,12] thanks to 5d-4f transition, while Eu 3+ ions have been shown to exhibit narrow emissions in the red, blue and green regions corresponding to f −f transitions [11][12][13][14][15][16]. ...
Conjugated BaI2:Eu (5 at.%) nanocrystalline particles were synthesized, decorated with golden nanoparticles (GNP). GNP demonstrated some hydrophilic effect, leading to the BaI2·H2O phase creation. The Eu2+ luminescence intensity was reduced according to the GNP content. This was due to the decreased number of Eu2+ ions in the BaI2, most probably, arising from the Au substitution for Ba competing with Eu. Moreover, the decay time of luminescence was decreased upon GNP content. This was explained by the moderation of negative charge in the GNP, leading to the repulsion with an electron in the excited Eu2+.
... The absorption spectra of all four glasses under consideration are presented in Fig. 1 (a), where the absorption features distinctive of Eu 3+ , Dy 3+ , and the surface plasmon resonance (SPR) of Cu NPs, are pointed out. The spectra exhibit absorption bands indicative of the presence of: (i) Eu 3+ ions, small peak around 394 nm (3.15 eV) due to 7 F 0 → 5 L 6 transition [22]; (ii) Dy 3+ ions, e.g., band at about 1274 nm (0.97 eV) due to 6 H 15/2 → 6 F 11/2 + 6 H 9/2 transitions [13]; and (iii) Cu NPs, SPR band around 570 nm (~2.2 eV) [17,23,24]. It is noticed in Fig. 1 (a) that the NDEuDyCu parent glass lacks the absorption band characteristic of copper (II) which, if present, manifests broadly towards longer wavelengths >600 nm [14][15][16]. ...
Phosphate glasses containing Eu2O3, Dy2O3 and CuO were melted together with nanodiamond (ND) powder for an assessment of optical and plasmonic properties aiming for the tuning of light-emitting properties towards photonic applications. A thorough evaluation incorporating optical absorption, differential scanning calorimetry, Raman scattering, and photoluminescence (PL) spectroscopy was carried out. The presence of ND allowed for the stabilization of the Cu⁺ ions with blue-emitting character alongside the yellow-emitting Dy³⁺ and red-emitting Eu³⁺ ions thus allowing for attaining the white light-emitting glasses. Further heat treatment within 470–490 °C of the tri-doped glass resulted in the development of the surface plasmon resonance (SPR) characteristic of Cu nanoparticles (NPs). A strong correlation of the optical bandgaps with SPR development is revealed. Further, a novel approach for assessing the activation energy for Cu NP precipitation is proposed linked to the glass transition temperature of the host. Subsequently, the effect of the plasmonic character on the PL properties was evaluated and correlated to the emission color. Correlated color temperature and chromaticity shifts were assessed and analyzed. The study contributes to the fundamental understanding and design of materials for tunable white light-emitting devices and the influence of incorporating plasmonic nanostructures attractive for photonic applications.
Glass ceramics in the form of MI2:Eu crystalline particles grown in MO-B2O3 glass (M = Ca, Sr, Ba) through recrystallization from the alloyed melt were fabricated. Eu²⁺ ions were detected in the CaI2 and SrI2 crystalline particles (not in the BaI2) inside the corresponding glasses. Some amount of Eu²⁺ centers are expected to originate from the MO-B2O3 glass hosts as well. This was confirmed by correlated electron paramagnetic resonance (EPR), photo- and radioluminescence (PL, RL) measurements. Peculiarities of the Eu²⁺ distribution and incorporation into the glass ceramics samples as well as charge and energy transfer properties are discussed in detail. Optimal conditions leading to the enhancement of the Eu²⁺ emission from the CaI2 and SrI2 crystallites inside the glasses were determined.
Calcium fluoride-bismuth oxide-phosphate glass of (60-x)P2O5-25Bi2O3-14CaF2-1Sb2O3-xEu2O3 (PBCFS), (x = 0, 0.25, 0.5, 0.75, and 1 mol%) was manufactured by melt-quenching technique. XRD and FT-IR spectra were obtained to characterize the PBCFS glass structure. The glass density, molar volume, refractive index, and thermal properties were determined. The absorption spectra of the PBCFS glass had three absorption peaks. The absorption peak with the highest intensity corresponded to the electronic transition of ⁷F0→⁵L6 (∼392 nm), and the electronic transition starting from the first excited state (⁷F1) was also found. The excitation spectra corresponding to the ⁵D0→⁷F2 transition of Eu0.5 at 612 nm was obtained. When excited by a λex = 392 nm xenon lamp, the strongest orange-red emission occurred at 612 nm (⁵D0→⁷F2). According to the CIE1931 chromaticity coordinates, the chromaticity coordinates of the PBCFS glass with different Eu2O3 contents were determined by the emission spectra. The decay curve of Eu³⁺ ions with ⁵D0→⁷F2 (612 nm) transition was obtained by monitoring the excitation at λex = 392 nm, which was compared with other Eu³⁺-doped luminescent glass. The color tunability of the orange-red light emission of the Eu³⁺ ions indicated that Eu³⁺-doped PBCFS glass may be suitable for LEDs and display device applications.
Raman spectroscopy studies of alkali and alkaline earth silicate glasses and melts are reviewed, and the major Raman bands observed are summarized. To realize the full potential of Raman spectroscopy will require a detailed understanding of their vibrational properties in relation to structure. A number of vibrational calculations have been carried out to address this problem. These are briefly summarized, and some limitations of the method are noted. Systematic variations in bulk properties are examined for viscosity and the immiscibility behavior.
.
IR and Raman spectroscopies have been utilized to study the structure and vibrational modes of sol–gel-derived binary silicate
glasses. The present study is motivated by the immense geological significance and focuses on the MO–SiO
2
(M = Ca, Mg) binary systems in an effort to unveil the role of the CaO and MgO modifiers when incorporated to the 3D silica
structure. Glasses in the composition range
x
=0, 0·1, 0·2, 0·3 and 0·4 prepared by the sol–gel method were compared with the corresponding glasses formed by appropriate
mixing of SiO
2
and MO powders through melting and fast cooling. The vibrational spectra of the sol–gel-derived glasses have revealed considerable
changes in relative intensities as a function of the MO mole fraction. These changes signify structural modifications on the
silica network. The population of the
Q
3
species was found to increase for both modified silicate systems. The rate of increase is more pronounced in the CaO–SiO
2
glasses. The extent of network depolymerization in the porous glass is higher at the same content of alkaline earth oxide
compared to the bulk glass. The results are indicative of a more ‘defective’ nature of the sol–gel glasses compared to the
corresponding melt-quenched ones.
Eu-doped and Eu/Al-codoped high silica glasses (HSGs) are prepared by infiltration and densification method. Absorption, photoluminescence and electron spin resonance (ESR) spectra of the Eu-doped high silica glasses (HSGs) are measured and the results indicate the reduction of Eu3+ to Eu2+ ions partly in Eu/Al-codoped HSGs. Energy transfer between Eu2+ ions and Eu3+ ions is observed and this transfer enhances the intensity of Eu3+ ions. The reduction mechanism is also discussed.
A ‘crystal-chemistry’ model is proposed to evaluate the rare-earth local structure in glass based on the modified-random-network (MRN) model in glass structure. Three influential factors are summarized, concerning the coordination number, the regularity of the site around the ion, and the spacing between ions. The spectral properties of rare-earth ions in glasses is well described and predicted by the proposed ‘crystal-chemistry’ model. The concentration-quenching effect of rare-earth ions in glasses in terms of ion-ion separation is analyzed by this model in relation to the role as glass-modifier or glass-intermediate of the rare-earth ion in the glass. The model suggests that glasses in which the rare-earth ions act as intermediates are likely to show less concentration-quenching effect.
Electron spin resonance (ESR) spectra of Eu2+ and Tb4+ were observed at room temperature in one fluoride phosphate and two phosphate glasses. Although both ions are isoelectronic, they have different ESR spectra. Eu2+ ions exhibit pronounced features at effective g-values of 2.0, 2.8 and 6.0, which is typical for the so-called U-spectrum. Tb4+ ions give only a single feature at g = 5.0. The different spectra are due to different crystal field strengths. The higher charge of Tb4+ ions results in a stronger local field compared with Eu2+ ions.
Eu2O3-doped aluminoborosilicate glasses were prepared by melting in air at high temperature (1500 8C). It was shown by luminescence and Electron Paramagnetic Resonance (EPR) measurements that both Eu3+ and Eu2+ ions can exist simultaneously in the glass matrix studied after glass synthesis as well as after exposure to ionizing radiation. Increase of total Eu2O3 concentration leads to the increase of Eu3+ luminescence intensity while the luminescence intensity of Eu2+ ions tends to decrease. In contrast the EPR indicates that the amount of Eu2+ ions in the glass increases with total Eu2O3 concentration. The difference in the results of the two spectroscopies is explained in terms of energy transfer from Eu2+ to Eu3+ leading to an Eu2+ luminescence quenching. Irradiation results in the increase of reduced Eu2+ quantity detected by EPR measurements. It was shown that Eu2+ ions are located in both high (g 4.6) and low symmetry (‘‘U' spectrum) sites in the structure of aluminoborosilicate glasses. The increase of Eu2+ content by the increase of the irradiation dose manifests the strong reduction process Eu3+!Eu2+.
Novel glasses and glass ceramics with compositions corresponding to stoichiometric lithium and barium disilicates and doped with different combinations of Ce³⁺, Eu2+,3+, Tb³⁺, and Dy³⁺ have been fabricated and studied as prospective light converters for white high-power light emitting diodes and laser diodes. Spatially resolved photoluminescence spectroscopy and structural analysis have been employed. The emission spectra and CIE color coordinates of these materials evidence their good prospective as phosphors for white light sources. Structural analysis proves a high level of crystallization of the ceramics fabricated by annealing the glasses, while spectroscopic study revealed the influence of crystallization on the emission properties of this system. The results show a high potential of these materials be exploited as temperature-resistant phosphors in high-power white light emitting diodes.
Photo- and radioluminescent properties of lithium silicate glasses doped with Ce³⁺and Tb³⁺ions were evaluated. Glasses doped with Ce³⁺ ions exhibit a shift of radioluminescence to photo-luminescence band. This effect was explained by a distribution of the crystal field strength in the activator sites, what results in the competition between different types of Ce³⁺ ions in absorbing excitation energy from the matrix and limits a light yield of the Ce³⁺ doped glass. We also investigated the possibility to use Tb³⁺ ion instead of Ce³⁺ as an alternative activator for a glass doping. Spin-orbit interaction plays a major role in the formation of electronic terms in Tb³⁺, where as an effect of the crystal field is small enough to form a distribution of emitting centers. Tb³⁺-doped samples demonstrate light yields up to 31000 ph/MeV with the concentration quenching starting at the levels of 10 at %. We also studied the effect of luminescence sensitization of Tb³⁺ ions by Ce³⁺ in the glasses co-doped with Ce³⁺ and Tb³⁺.
Set of Eu-doped Y3Al5O12 (YAG) phosphors in the powder form was successfully synthesized by multiple-step solid state reaction under the reducing Ar:5%H2 atmosphere. Their physical properties were investigated by means of X-ray diffraction, time-resolved luminescence spectroscopy and electron paramagnetic resonance (EPR). Special attention was given to well-grounded confirmation of Eu2+ occurrence in the YAG structure. X-ray diffraction confirmed the presence of major YAG phase in all samples. The influence of Eu concentration, form of doping (EuS, EuF2 or Eu2O3) and a number/form of annealing steps was studied. Corresponding characteristics were measured and evaluated in a broad temperature range (8 – 800 K). The correlated measurements showed that the single Eu2+ ions stabilized in YAG in the yttrium position are responsible for the 440 nm emission. The corresponding lowest energy excitation band is situated at 300 nm and the radiative lifetime of Eu2+ emission is about 500 nanoseconds. Phenomenological model of excited state dynamics was used to explain the experimentally observed features. Possible practical exploitation of Eu2+ center in the YAG host is discussed.
Existing states of silver depend on the sintering temperature in the SiO2 three-dimensionally ordered macroporous (3DOM) materials. Several species related to the silver (Ag+ ions, Ag+–Ag+ and Ag nanoparticles) were demonstrated in the SiO2 3DOM materials prepared by 550 oC. Only Ag nanoparticles were observed in the SiO2 3DOM materials prepared by 750 oC. The influence of silver species on photoluminescence properties of Eu3+ was investigated systematically in the SiO2 3DOM materials. The results show that photoluminescence enhancement of Eu3+ ions was obtained by Ag species in the SiO2 3DOM materials. For the SiO2 3DOM materials prepared by 550 oC, the enhancement of Eu3+ luminescence is attributed to energy transfer from Ag+–Ag+ to Eu3+ under the excitation of 345 or 280 nm, while luminescence enhancement of Eu3+ is due to energy transfer from isolated Ag+ to Eu3+ under the excitation of 245 nm. For the SiO2 3DOM materials prepared by 750 oC, the luminescence of Eu3+ were enhanced due to plasmon resonance effect of Ag nanoparticles.
Electron paramagnetic resonance and luminescence spectroscopies were applied to study the incorporation and charge stability of Eu2+ luminescent ions in single crystals of KLuS2:Eu found in an earlier optical study [Jary et al., Chem. Phys. Lett. 574, 61 (2013)]. The location of Eu2+ in the structure was unambiguously determined and three different centers were identified and described. Two of these centers correspond to substitution of Eu2+ for K+ and Lu3+ ions providing thus effective mechanism for Eu2+ incorporation due to the charge self-compensation in the lattice. The observed luminescence spectra are consistent with the results of electron paramagnetic resonance experiment and can be decomposed accordingly. ((c) 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)
The problem of Eu incorporation into silica as dispersed dopants, clusters, separate-phase nanoparticles, or nanocrystals, which is of key importance for applications in the fields of lasers and scintillators, is faced by applying to sol− gel silica doped with nine different Eu 3+ concentrations (0.001−10 mol % range) various spectroscopic techniques, including crystal field and vibrational mode analysis by means of Fourier transform absorption and microreflectivity (in the 200−6000 cm −1 and 9−300 K ranges), radioluminescence, and Raman scattering studies at 300 K. The variety of methods revealed the following concordant results: (1) amorphous Eu clusters grow when the Eu concentration is increased up to 3 mol % and (2) Si−OH groups are completely removed and ordered phase separation occurs at 10 mol % doping, as suggested by the remarkable narrowing of the spectral lines. Comparison with polycrystalline Eu oxide, Eu silicates, and α-quartz spectra allowed the unequivocal identification of Eu 2 Si 2 O 7 pyrosilicate and α-quartz as the main components of nanocrystals in 10 mol % Eu-doped silica. Such conclusions were brilliantly confirmed by transmission electron microscopy and electron diffraction analysis. Phonon coupling and anharmonicity were analyzed and are discussed for a few vibrational modes of nanocrystals.
Phase transformation sequences of SrOAl2O3 have been investigated at 1000 and 1250 °C through XRD technique along with emission signatures of Eu2+ and Eu3+. Two phases, i.e., [Sr3Al2O6] and [SrAl2O4], have been observed at 1000 °C as stable phases. These phases were found to be transformed into [SrAl2O4] at 1250 °C.
Absorption, fluorescence and optical excitation spectra of the Eu2+ and Eu3+ ions in Al2O3–SiO2 glass prepared by the sol–gel method are investigated. When the Eu3+-doped glass is heated in H2, the Eu3+ ions are almost reduced to the Eu2+ ions. By reheating of the Eu2+-doped glass in air, the fluorescence intensity for the Eu2+ ions decreases, and the fluorescence intensity for Eu3+ ions increases with increasing the heating time and is saturated to 1.5 times of the intensity before heating in H2. This significant increase in the Eu3+ fluorescence is related to the energy transfer from Eu2+ ions to Eu3+, in which the energy corresponding to the 4f65d(Eg)→8S7/2 transition of the Eu2+ ion causes to excite the Eu3+ ion to the 5D2 state. When the Eu2+-doped glass is irradiated with a Hg lamp for 2 h, the fluorescence intensity for the Eu3+ ions returns no more than 10% of the intensity before heating in H2. This behavior is thought to be related to the capturing of the excited electrons in the trapping centers near the Eu2+ ions.
Raman spectra of CaOSiO2 and CaOSiO2CaF2 glasses were measured to analyze three states of oxygen, i.e. bridging, non-bridging and free oxygen, in a similar way to the previous work on PbOSiO2 glasses. The stretching vibrational modes of the SiO bond in CaOSiO2 and CaOSiO2CaF2 glasses corresponded to the bands at 880, 920, 975 and 1050 cm−1. It is suggested from the comparison of the Raman spectra of the glasses with the Raman and infrared absorption spectra of crystalline silicates that these bands would arise from the SiO4 tetrahedron with four, three, two and one non-bridging oxygens, respectively. The fractions of bridging, non-bridging and free oxygens were calculated from the intensities of the four Raman bands and the composition of the glasses. They were in agreement with those obtained from the thermodynamical model for the CaOSiO2 glasses. When the content of CaF2 was smaller than 15–20 mol.% and the ratio was smaller than unity, CaF2 contributed to the breakage of some SiO bonds.
Fabrication of EuO-Al2O3-B2O3-SiO2 glasses with high-concentration of EU2+ ions was attempted in N-2 gas with an IR-image furnace and rapid quenching in twin rollers. Their magnetic susceptibilities of these glasses obeyed the Curie-Weiss law with the negative Curie temperature at temperatures higher than 50 K, while EU2+ ions coupling by a superexchange-type mechanism involving oxygen ions at temperatures lower than 50 K showed a ferromagnetism. From their magnetization data at lower temperatures, we estimated an amount of EU2+ ions in the glasses, in whose fabrication process a part of EU2+ ions were oxidized to Eu3+. We also measured FT-IR and Raman spectra and discussed the stable valence state of europium ions in the studied glass-matrixes.
The novel phosphor of LaAlGe2O7 activated with the trivalent rare-earth Ln3+ (Ln=Eu, Sm, Dy) ions were synthesized by solid-state method, and their characterization and luminescent properties were investigated. The absorption, emission and excitation spectra, and decay curves were employed to study the luminescence properties. The calcined powders of the Eu3+, Sm3+ and Dy3+ ions doped in the LaAlGe2O7 emit bright red, reddish orange and yellowish white light, respectively. In the photoluminescence investigations, there is a single and highly symmetric site for activator ions in the LaAlGe2O7 host lattice. The sharp emission properties show that the LaAlGe2O7 is a suitable host for rare-earth doped laser crystal and phosphor material.
In order to assign the bands in the IR spectra of silicates to the appropriate normal vibrations, a vibrational model has been proposed. A complex silicooxygen ring is considered as a `unit cell' composed of the appropriate number of [SiO4]4− tetrahedra. According to this model, in the ring silicates spectra we have to observe bands due to internal vibrations of individual tetrahedra and bands corresponding exclusively to the ring structure. Change in the tetrahedra symmetry from Td (ideal tetrahedron) to C2v (tetrahedron in a ring) and then to the ring symmetry: D3h, D4h and D6h (ideal rings) with respect to reducible representations makes it possible to differentiate between the bands due to ring structure (pseudo-lattice vibrations) and internal modes of tetrahedra. It has been established that in the case of all ideal rings there is only one IR active vibrational mode, namely the one symmetric with respect to the axis of the highest fold, i.e. A2″ in the case of 3-membered rings and A2u in the case of 4- and 6-membered rings. The model proposed has been verified for different membered ring silicates.
The refractivity of the oxide ion, RO2−, in alkali and alkaline-earth silicate glasses is shown to vary linearly with the optical basicity calculated from the basicity moderating parameters of the constituent cations. Deviations in the relationship are almost eliminated by adjusting the refractivity values of the cations. The relationship allows the basicity moderating parameters to be estimated for cations with previously unassigned values, for example, Pb2+ in lead silicate glasses and Zr4+ in zirconium silicate glasses. Although the relationship appears to extend satisfactorily to ternary glass systems, e.g. K2OAl2O3SiO2, it becomes less straightforward when structural changes occur in the glass, for instance in the sodium borate system. These structural changes are often detected by the optical basicity trends signalled by probe ions, and it is suggested that refractivity measurements could indicate areas for which investigation by probe ion spectroscopy is profitable.
Solid state blue and green light sources are desirable for high density optical storage, color displays, optoelectronics, and medical diagnostics. In addition to the well-known red emission of Eu3+, strong green, blue, and ultraviolet emissions have been observed in Eu3+ doped ZBLA (57ZrF4·36BaF2·4LaF3·3AlF3) and PIGLZ (43PbF2·17InF3·17GaF3·4LaF3·19ZnF2) fluoride glasses. The intense concentration dependence of these emissions was examined with fluorescence and excitation spectroscopy and found to be caused by nonradiative dipole-quadrupole and dipole-dipole energy transfer between excited and ground state Eu3+ ions. Judd-Ofelt analysis, transfer efficiency, and phonon side band measurements were used to model the fluorescence, energy transfer, and gain cross section for Eu3+ in a ZBLA host.
Phase transformation sequences of SrO-AlâOâ have been investigated at 1,000 and 1,250 C through XRD technique along with emission signatures of Eu{sup 2+} and Eu{sup 3+}. Two phases, i.e., [SrâAlâOâ] and [SrAlâOâ], have been observed at 1,000 C as stable phases. These phases were found to be transformed into [SrAlâOâ] at 1,250 C.
In most amorphous insulating magnets, the magnetic structure is dominated by the random distribution of magnetic moments as well as the predominant antiferromagnetic interaction among them, inevitably leading to a transition from high-temperature paramagnetic to low-temperature spin glass phase. In this paper, we report our discovery of ferromagnetic amorphous oxides with reentrant spin glass behavior. Unlike most oxide glasses, there is a strong tendency for the magnetic interaction of Eu2+ ions to be ferromagnetic in oxide glasses, as obviously indicated by the positive values of Weiss temperature. Comprehensive investigations of low-temperature magnetic properties for the present Eu2+ -containing glasses have revealed a typical behavior of reentrant ferromagnets. We discuss the possible mechanisms behind the ferromagnetic interactions, as well as the origin of reentrant spin glass nature, based on the specific electronic structure of Eu2+ compounds.
Rare-earth-doped fluorochlorozirconate (FCZ) glass-ceramic materials have been developed as scintillators and their properties investigated as a function of dopant level. The paper presents the relative scintillation efficiency in comparison to single-crystal cadmium tungstate, the scintillation intensity as a function of x-ray intensity and x-ray energy, and the spatial resolution (modulation transfer function). Images obtained with the FCZ glass-ceramic scintillator and with cadmium tungstate are also presented. Comparison shows that the image quality obtained using the glass ceramic is close to that from cadmium tungstate. Therefore, the glass-ceramic scintillator could be used as an alternative material for image formation resulting from scintillation. Other inorganic scintillators such as single crystals or polycrystalline films have limitations in resolution or size, but the transparent glass-ceramic can be scaled to any shape or size with excellent resolution.
A novel Eu2+ ion doped triple phosphate Ca8MgGd(PO4)7 was synthesized by a general high-temperature solid-state reaction in a reductive atmosphere. X-ray powder diffraction analysis confirmed the formation of single phase Ca8MgGd(PO4)7. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 1–2 µm. Photoluminescence excitation spectrum measurements show that the phosphor can be efficiently excited by UV–visible light from 250 to 480 nm to realize emission in the visible range. The emission spectrum showed a broad and asymmetric profile from 410 to 750 nm, which corresponds to the allowed f–d transition from three kinds of Eu2+ ions. The characteristics indicated that this phosphor is a candidate for application in the white light-emitting diodes. The luminescence mechanism and three site occupancies of Eu2+ ions in Ca8MgGd(PO4)7 lattices are briefly discussed.
Ce3+-doped high silica glass was prepared by impregnation of Ce ions into a porous silica glass followed by high temperature sintering in a CO reducing atmosphere. The characteristic emission of Ce3+ 5d → 4f transition peaking around 375 nm is observed in its luminescence spectra under UV and X-ray excitation. Its photoluminescence decay is governed by several tens of nanoseconds decay time. Its integral scintillation efficiency is comparable to that of a Bi4Ge3O12 (BGO) crystal under X-ray excitation. Scintillation light yield under gamma and alpha excitation was measured and compared with that of BGO.
The Eu2+-doped NaBaPO4 phosphor was prepared by high-temperature solid-state reaction. The photoluminescence excitation and emission spectra and the luminescence quantum efficiency of Eu2+ ions were investigated. The dependence of luminescence intensity on temperatures and the temperature-dependent decay times of Eu2+ ions doped in NaBaPO4 were measured and discussed. The natures of the Eu2+ emission in NaBaPO4, e.g., the Stokes shift, the luminescence quenching temperature (T0.5), the activation energy for thermal quenching (δE) were reported. In addition, the crystal structure and the site occupancy of Eu2+ ions doped in NaBaPO4 crystal lattice were discussed. Two different Eu2+ centers were assigned according to the crystal structure and the luminescence characteristics of Eu2+ ions. The phosphor shows an excellent thermal stability on temperature quenching effects. With the increasing of temperature, the emission bands show the abnormal blue-shift.
Transparent glass-ceramics have been prepared by heat-treating 45SiO2–20Al2O3–10CaO–25CaF2 glasses doped with Eu2+ ions (in mol%). The precipitated crystalline phase in the glass-ceramics was CaF2. TEM observation showed the precipitated crystalline phase had a size of 11–18 nm and dispersed in the amorphous phase without clustering. Fluorescence measurements showed that Eu2+ ions entered into the CaF2 crystalline phase and gave a much stronger emission in the glass-ceramics than in the corresponding glass.
The variations of emission intensities of SrB4O7:Eu2+ and Sr2B5O9Cl:Eu2+ prepared in different atmospheres are discussed in view of the structure of host compounds. A model of substitution defects is proposed to explain the abnormal reduction of Eu3+→Eu2+ in non-reducing atmospheres of N2, air and O2. Experiment results show that SrB4O7:Eu2+ phosphor sample prepared in N2 atmosphere has an emission intensity of 94% as high as that of the sample prepared in H2 gas. This implies that the reduction of Eu3+→Eu2+ in non-reducing atmospheres could be potentially used in preparing phosphors, such as SrB4O7:Eu2+.
Eu3+ doped alkali–barium–bismuth–tellurite (Eu3+:LKBBT) glasses were prepared by conventional melt quenching. Twelve emission bands including infrequent blue and green bands are observed and they almost cover whole visible spectral region under violet light radiation. The blue and green emissions of Eu3+ rarely appeared in oxide glasses before, but they have been clearly recorded in Eu3+:LKBBT glasses even in the case of high concentration doping of Eu3+. The analysis based on spontaneous-radiative rate, energy gap and Raman scattering reveals that the obtaining of the abundant multichannel emissions of Eu3+ is due to the higher refractive index and the lower phonon energy in LKBBT glass system.
Eu3+-doped transparent nanocomposite of SiO2–Al2O3–NaF–LaF3 was fabricated by melt-quenching and subsequent heating. X-ray diffraction and transmission electron microscopy analyses evidenced that hexagonal LaF3 nanocrystals were homogeneously precipitated among the aluminosilicate glass matrix. The distribution of Eu3+ ions in the nanocomposite was investigated by energy dispersive X-ray spectroscopy, photoluminescence and time-resolved luminescence spectra. The nanocomposite exhibited intense blue and green emissions originating from the 5D1,2,3 levels of Eu3+ incorporated in the low-phonon-energy LaF3 nanocrystals, and red emission corresponding to the Eu3+:5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions, under the excitation of single wavelength light at 394 nm. By adjusting the Eu3+ doping content, various luminescent colors, including perfect white light, were easily tuned through cross relaxation processes between Eu3+ ions. The results suggest that the Eu3+-doped transparent nanocomposite could be potentially applicable as a white-light-emitting material under UV chip excitation.
Calcium alumino–silicate glasses were investigated by infrared reflectivity and polarized Raman scattering. Vibrational modes were assigned to different types of atomic motion in the glass network. The nature of the low frequency Raman peak or Boson Peak is discussed in terms of existing theories. Kramers–Kronig analysis was performed on IR reflectivity data to extract longitudinal and transverse optic phonon frequencies.
Some aspects of the interpretation of IR spectra of inorganic solids are discussed, with emphasis on the factors influencing the vibrational frequencies of cation-oxygen co-ordinated groups, namely the value of the co-ordination number, “isolated” or “condensed” state of the co-ordinated groups and vibrational interactions with neighbouring groups. These considerations are applied to the study of AlO stretching frequencies in a series of aluminates.Characteristic frequency ranges are as follows:“Condensed” AlO4 tetrahedra 900-700 cm−1, “Isolated” AlO4 tetrahedra 800-650 cm−1, “Condensed” AlO6 octahedra 680-500 cm−1, “Isolated” AlO6 octahedra 530-400 cm−1.Several cases of mixed vibrations (AlO + LiO) are found in the particular case of lithium aluminates from abnormal or erratic 6Li7Li isotopic shifts.
Phosphate (P2O5+K2O+BaO+Al2O3+Eu2O3) and fluorophosphate (P2O5+K2O+BaO+BaF2+Al2O3+Eu2O3) glasses with different Eu3+ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the 5D0 emitting level of Eu3+ ions in these glasses. The relative luminescence intensity ratio of 5D0→7F2→5D0→7F1 transitions has been evaluated to estimate the local site symmetry around the Eu3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5D0→7F1 and 5D0→7F2 transitions. Second and fourth rank crystal-field (CF) parameters have been calculated together with the CF strength parameter by assuming the C2v symmetry for the Eu3+ ions in both the phosphate and fluorophosphate glasses. Judd–Ofelt parameters have been evaluated from the luminescence intensity ratios of 5D0→7FJ (J=2, 4 and 6) to 5D0→7F1 transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the 5D0→7FJ transitions. Decay curves of the 5D0 level of Eu3+ ions in these two Eu3+:glass systems have been measured by monitoring the 5D0→7F2 transition (611 nm) at room temperature. The experimental lifetime of the 5D0 level in the title glasses is found to be higher than Eu3+-doped niobium phosphate glasses. The analysis indicates that the lifetime of the 5D0 level is found to be less sensitive to the Eu3+ ion concentration and addition of BaF2 has no significant effect on the optical properties of Eu3+-doped phosphate glasses.
The optical, magnetic and structural properties of Eu doped low silica calcium aluminosilicate glasses were investigated. The optical absorption coefficient presented two bands at 39,246 and 29,416 cm(-1), which were assigned respectively to the [Formula in text], and [Formula in text] transitions of Eu(2+). The fluorescence measured at 300 K on a sample doped with 0.5 wt% of Eu(2)O(3) exhibited a broad band centered at 17,350 cm(-1), which is attributed to the [Formula in text] transition of Eu(2+), whereas the additional peaks are due to the [Formula in text] transitions of Eu(3+). From magnetization and XANES data it was possible to evaluate the fractions of Eu(2+) and Eu(3+) for the sample doped with 0.5 and 5.0 wt% of Eu(2)O(3), the values of which were approximately 30 and 70%, respectively.
We present a detailed analysis of the luminescence behavior of europium-doped hydroxyapatite (HAp) and calcium-deficient hydroxyapatite (Ca-D HAp) nanopowders. The results show that, while both powders are similar in crystallite size, particle size, and morphology, the luminescence behavior differs significantly. For the HAp:Eu powders, the emission is clearly from Eu(3+) ions and corresponds to typical (5)D(0) --> (7)F(J) emissions, whereas for the Ca-D HAp:Eu powders, we also see a broad emission with two peaks at 420 and 445 nm, corresponding to the 4f(6)5d(1) --> 4f(7) ((8)S(7/2)) transition of Eu(2+). The powders are weakly luminescent in the as-synthesized state, as expected for combustion-synthesized materials and have higher emission intensities as the heat treatment temperature is increased. Luminescence spectra obtained using an excitation wavelength of 254 nm are weak for all samples. Excitation wavelengths of 305, 337, and 359 nm, are better at promoting the Eu(3+) and Eu(2+) emissions in hydroxyapatites. We propose that fluorescence measurements are an excellent way of qualitatively determining the phase composition of europium-doped hydroxyapatite powders, since powders that exhibit a blue emission contain substantial amounts of Ca-D HAp, allowing the determination of the presence of this phase in mixed-phase hydroxyapatites.
We report what is believed to be the first observation of permanent photoreduction of Eu(3+) to Eu(2+) in transparent and colorless Eu(3+) -doped fluorozirconate glass at room temperature, using an infrared femtosecond laser. Difference absorption and electron-spin-resonance spectra of the glass before and after laser irradiation showed that a portion of the Eu(3+) ions in the focused part of the laser inside the glass were reduced to Eu(2+) ions after laser irradiation. It is suggested that Eu(3+) ions act as electron-trapping centers, whereas active sites in the glass matrix act as hole-trapping centers, leading to the formation of Eu(2+) ions. The observed phenomenon is inferred to be useful in the fabrication of optical memory devices with high storage density and waveguide-type micro-optical devices.
Diffusion limited reactions of point defects were investigated in amorphous SiO2 exposed to UV laser light. Electron spin resonance and in situ absorption measurements at room temperature evidenced the annealing of E′ centers and the growth of H(II) centers both occurring in the post-irradiation stage and lasting a few hours. These transients are caused by reactions involving molecular hydrogen H2, made available by dimerization of radiolytic H0. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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