The photoluminescent properties of Eu in MgO-Ga2O3-SiO2 nanocrystalline glass-ceramic

The MgO-Ga₂O₃-SiO₂ glass-ceramic (GC) containing MgGa₂O₄ nanocrystals and glasses doped with Eu³⁺ ions were prepared by the sol-gel method. The down-conversion and up-conversion luminescence (UCL) properties were studied. The results indicated that the relative intensity of f-f transitions of Eu³⁺ decreased in contrast with that of charge transfer (CT) absorption with the increase in heating temperature. Using a Xe lamp and 800 nm femtosecond (fs) laser excitation, strong red luminescence of Eu³⁺ in MgO-Ga₂O₃-SiO₂ glasses and GC was observed.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Role of Al2O3 in upconversion and NIR emission in Tm and Er codoped calcium fluoro phosphorous silicate glass system

In this study, the principal role of Al₂O₃ on the features of the photoluminescence spectra of Tm³⁺ ion and upconversion phenomenon in Tm³⁺ and Er³⁺ codoped CaF₂−Al₂O₃−P₂O₅−SiO₂ glass system has been investigated. The concentration of Al₂O₃ is varied from 2 to 10 mol% while that of Er³⁺ and Tm³⁺ is fixed. IR and Raman spectral studies have indicated that there is a gradual increase in the degree of disorder in the glass network with increase in the concentration of Al₂O₃ up to 6.0 mol%. This is attributed to the presence of Al³⁺ ions in octahedral positions in larger proportions. When the glasses are doped with Tm³⁺ ions, the blue and red emissions were observed, whereas in Er³⁺ doped glasses blue, green and red emissions were observed. When the glasses are codoped with Tm³⁺ and Er³⁺ ions and excited at 790 nm, all the three emission lines were observed to be reinforced, especially in the glasses mixed with 6.0 mol% of Al₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄→³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to codoping. The reasons for enhancement in the intensity of various emission bands due to codoping have been identified and discussed with the help of rate equations for various emission transitions.     

Redox equilibrium of samarium ions doped in Al2O3-SiO2 glasses

Redox reaction of samarium ions doped in Al₂O₃-SiO₂ glasses, prepared by a rapid cooling technique of the melts, was examined by the measurement of the optical absorption and fluorescence properties. It was found that the doped samarium ions are easily reduced and oxidized by heating in H₂ and O₂ gases, respectively. The redox kinetics of samarium in the H₂ and O₂ atmospheres obey good first-order kinetics. The activation energy for the Sm³⁺ reduction in the 10Al₂O₃90SiO₂ glass was estimated to be ∼70 kJ/mol, which decreased with the increasing Al₂O₃ content. On the other hand, the activation energies for the oxidation were ∼90 kJ/mol, which only slightly depends on the glass composition. In these glasses, the samarium ions are preferentially surrounded by the Al-O polyhedra, where the oxygen ions are easily removed to form defect centers. It was concluded that the movement of the oxygen ions in the Al-O polyhedra determine the redox equilibrium of the samarium ions.     

Luminescent properties of green- or red-emitting Eu-doped Sr3Al2O6 for LED

Eu²⁺-doped Sr₃Al₂O₆ (Sr_3−xEu_xAl₂O₆) was synthesized by a solid-state reaction under either H₂ and N₂ atmosphere or CO atmosphere. When H₂ was used as the reducing agent, the phosphor exhibited green emission under near UV excitation, while CO was used as the reducing agent, the phosphor mainly showed red emission under blue light excitation. Both emissions belong to the d-f transition of Eu²⁺ ion. The relationship between the emission wavelengths and the occupation of Eu²⁺ at different crystallographic sites was studied. The preferential substitution of Eu²⁺ into different Sr²⁺ cites at different reaction periods and the substitution rates under different atmospheres were discussed. Finally, green-emitting and red-emitting LEDs were fabricated by coating the phosphor onto near UV- or blue-emitting InGaN chips.     

Phosphorescent and thermoluminescent properties of SrAl2O4:Eu,Dy phosphors prepared by solid state reaction method

Long persistent SrAl₂O₄:Eu²⁺ phosphors co-doped with Dy³⁺ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl₂O₄ were observed in all the samples. The broad band emission spectra at 497 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ were observed and the emission is attributed to the 4f⁶5d¹ to 4f⁷ transition of Eu²⁺ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy³⁺ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence.     

Optical and fluorescence spectroscopy of Eu2O3-doped P2O5-K2O-KF-MO-Al2O3 (M = Mg, Sr and Ba) glasses

Fluorophosphate glasses of composition, P₂O₅ + K₂O + KF + MO + Al₂O₃ + xEu₂O₃ (M = Mg, Sr and Ba; x = 0.01, 0.05, 0.1, 1.0, 2.0, 4.0 and 6.0 mol%) were prepared and characterized their optical properties. Crystal-field (CF) analysis revealed a relatively weak CF strength around Eu³⁺ ions in the Ba based fluorophosphate glasses. The Judd-Ofelt parameters have been estimated from the oscillator strengths of ⁷F₀ → ⁵D₂, ⁷F₀ → ⁵D₄ and ⁷F₀ → ⁵L₆ absorption transitions of Eu³⁺ ions and were used to evaluate the radiative properties of the ⁵D₀ → ⁷F_J (J = 0-4) transitions. Considerable variation has been observed in the relative intensity ratio of ⁵D₀ → ⁷F₂ to ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions due to change in the alkaline earth metal ions. The decay of the ⁵D₀ level shows single exponential and less sensitive to Eu³⁺ ions concentration as well as MgO/SrO/BaO modifiers.     

Red, green and blue (RGB) emission doped Y3Al5O12 (YAG) phosphors prepared by non-hydrolytic sol-gel route

An evolutionary optimization process involving combination chemistry was employed in an attempt to develop Y₃Al₅O₁₂ (YAG). The combination chemistry process utilized here consisted the doping of the YAG host with appropriate amounts of red (R), green (G), and blue (B) dopants in a single layer, for use in tricolor white light. The doped YAG was acieved by means of the non-hydrolytic sol-gel route. Four samples were prepared, three of which were mono-doped samples containing 1.0% of a certain lanthanide (Eu³⁺, Tb³⁺, or Tm³⁺) ion, while the fourth contained the three ions. The samples were characterized by X-ray diffractometry and photoluminescence. The diffraction pattern of the mono-doped samples synthered at 800 °C for 16 h displayed peaks corresponding to the Y₃Al₅O₁₂ (YAG) phase, while the sample doped with the three ions revealed the presence of a mixture of Y₃Al₅O₁₂ (YAG) and Y₄Al₂O₉ (YAM) phases. The emission spectra of the three mono-doped YAG samples displayed the typical bands of the blue, green, and red emission of the corresponding lanthanide ions. As for the sample doped with the three lanthanide ions; it simultaneously emitted R, G and B lights. The green emission (546 nm) was more intense and narrow in relation to the red and blue emissions, which may be due to differences in the size of the three incorporated ions.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Synthesis and luminescence properties of nanocrystalline Gd2O3:Eu by combustion process

The nanocrystalline Gd₂O₃:Eu³⁺ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23 nm for the precursor and samples annealed at 600, 700 and 800 °C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O²⁻-Eu³⁺ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu³⁺ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu³⁺, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu³⁺ ions.     

Synthesis and luminous characteristics of Ba2MgSi2−xAlxO7: 0.1Eu, 0.1Mn phosphor for WLED

The shift of the emission band to longer wavelength (yellow-orange) of the Ba₂MgSi_2−xAl_xO₇: 0.1Eu²⁺ phosphor under the 350-450 nm excitation range has been achieved by adding the codoping element (Mn²⁺) in the host. The single-host silicate phosphor for WLED, Ba₂MgSi_2−xAl_xO₇: 0.1Eu²⁺, 0.1Mn²⁺ was prepared by high-temperature solid-state reaction. It was found experimentally that, its three-color emission peaks are situated at 623, 501 and 438 nm, respectively, under excitation of 350-450 nm irradiation. The emission peaks at 438 and 501 nm originate from the transition 5d to 4f of Eu²⁺ ions that occupy the two Ba²⁺ sites in the crystal of Ba₂MgSi_2−x Al_xO₇, while the 623 nm emission is attributed to the energy transfer from Eu²⁺ ions to Mn²⁺ ions. The white light can be obtained by mixing the three emission colors of blue (438 nm), green (501 nm) and red (623 nm) in the single host. When the concentrations of the Al³⁺, Eu²⁺ and Mn²⁺ ions were 0.4, 0.1 and 0.1 mol, respectively, the sample presented intense white emission. The addition of Al ion to the host leads to a substantial change of intensity ratio between blue and green emissions. White light could be obtained by combining this phosphor with 405 nm light-emitting diodes. The near-ultraviolet GaN-based Ba₂MgSi_1.7 Al_0.3O₇: 0.1Eu²⁺, 0.1Mn²⁺ LED achieves good color rendering of over 85.     

Eu/Tb ions co-doped white light luminescence Y2O3 phosphors

Y₂O₃:Eu³⁺, Tb³⁺ phosphors with white emission are prepared with different doping concentration of Eu³⁺ and Tb³⁺ ions and synthesizing temperatures from 750 to 950 °C by the co-precipitation method. The resulted phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. The results of XRD indicate that the crystallinity of the synthesized samples increases with enhancing the firing temperature. The photoluminescence spectra indicate the Eu³⁺ and Tb³⁺ co-doped Y₂O₃ phosphors show five main emission peaks: three at 590, 611 and 629 nm originate from Eu³⁺ and two at 481 and 541 nm originate from Tb³⁺, under excitation of 250-320 nm irradition. The white light luminescence color could be changed by varying the excitation wavelength. Different concentrations of Eu³⁺ and Tb³⁺ ions were induced into the Y₂O₃ lattice and the energy transfer from Tb³⁺→Eu³⁺ ions in these phosphors was found. The Commission International de l’Eclairage (CIE) chromaticity shows that the Y₂O₃:Eu³⁺, Tb³⁺ phosphors can obtain an intense white emission.     

Long lasting phosphorescence of Eu in reduced SrO-B2O3 glasses

The blue long-lasting phosphorescence (LLP) phenomenon was observed for Eu²⁺-doped SrO-B₂O₃ glasses prepared in the reducing atmosphere. The phosphorescence peaks at about 450 nm due to the 4f5d→4f transition of Eu²⁺. With the doping of different amounts of Eu²⁺, the concentration-quenching phenomenon was observed for both the LLP and photoluminescence of the glasses, and the critical concentration for the two cases was same, i.e., 0.02 mol% Eu²⁺. And by the investigation of the TL curves, the content of Eu²⁺ had an effect on the trap depth of the samples. At last the possible mechanism of the LLP of the samples was suggested.     

Auger electron/X-ray photoelectron and cathodoluminescent spectroscopic studies of pulsed laser ablated SrAl2O4:Eu,Dy thin films

Auger electron/X-ray photoelectron and cathodoluminescent (CL) spectroscopic studies were conducted on pulsed laser deposited SrAl₂O₄:Eu²⁺,Dy³⁺ thin films and the correlation between the surface chemical reactions and the decrease in the CL intensity was determined. The Auger electron and the CL data were collected simultaneously in a vacuum chamber either maintained at base pressure or backfilled with oxygen gas. The data were collected when the films were irradiated for 14 h with 2 keV electrons. The CL emission peak attributed to the 4f⁶5d¹ → 4f⁷ transitions was observed at ∼521 nm and the CL intensity of the peaks degraded at different rates in different vacuum conditions. X-ray photoelectron spectroscopy (XPS) data collected from degraded films suggest that strontium oxide (SrO) and aliminium oxide (Al₂O₃) were formed on the surface of the film as a result of electron stimulated surface chemical reaction (ESSCR).     

Dy含量对红色长余辉发光材料Sr3Al2Ｏ6:Eu2＋,Dy3＋性能的影响

采用溶胶凝胶法制备了Sr₃Al₂Ｏ₆:Eu^2＋,Dy^3＋红色长余辉发光材料,利用X射线衍射仪对材料的物相进行了分析,结果表明,1200℃下制备的样品的物相为Sr₃Al₂Ｏ₆,少量的Eu和Dy掺杂没有影响样品的相组成.采用荧光分光光度计、照度计测定了样品的发光特性.结果表明Sr₃Al₂Ｏ关键词： 红色长余辉 3Al₂Ｏ₆')" href="#">Sr₃Al₂Ｏ₆ 溶胶凝胶法     

超声喷雾共沉淀法制备的Lu3Al5O12∶Eu3+ 纳米粉体发光特性

采用新型超声喷雾共沉淀法技术,以Lu₂O₃、Eu₂O₃、Al(NO₃)₃·9H₂O为原料,制备了不同浓度Eu³⁺离子掺杂的Lu₃Al₅O₁₂纳米粉体.用X射线粉末衍射表征了获得纳米粉体的相,用扫描电镜观察了纳米粒子的形貌.测定了粉体的激发光谱、⁷F₀-⁵D₂声子边带谱与发射光谱.研究了不同高温烧结温度与Eu³⁺掺杂浓度对纳米粒子的发光强度与粒子形貌的影响规律.研究表明,当烧结温度高于900 ℃时,粉体发光强度明显增强,并且随着煅烧温度的增加,发光强度有所增强.Eu³⁺离子的最佳掺杂浓度为5~7 mol%.根据稀土离子Eu³⁺光学跃起矩阵元的特点,从发射光谱获得Eu³⁺光学跃起的J-O参量Ω₂与Ω₄.在Eu³⁺掺杂浓度均为5 mol%时,其强度参量达最小,电-声子耦合最强.然后随着掺杂浓度的进一步提高,强度参量略有增加,电-声子耦合减弱.说明Eu-O键强增加,共价性增强,Eu³⁺的局域环境对称性降低.Ω₂值低于Eu³⁺在玻璃与晶体基质中的情况,这是由于纳米粒子中存在着大量的缺陷以及晶体的结构畸变导致纳米粒子的对称性下降所致.     

Sensitized red luminescence from Bi co-doped Eu: ZnO-B2O3 glasses

Photoluminescence properties of Bi³⁺ co-doped Eu³⁺ containing zinc borate glasses have been investigated and the results are reported here. Bright red emission due to a dominant electric dipole transition ⁵D₀→⁷F₂ of the Eu³⁺ ions has been observed from these glasses. The nature of Stark components from the measured fluorescence transitions of Eu³⁺ ions reveal that the rare earth ions could take the lattice sites of C_s or lower point symmetry in the zinc borate glass hosts. The significant enhancement of Eu³⁺ emission intensity by 346 nm excitation (¹S₀→³P₁ of Bi³⁺ ions) elucidates the sensitization effect of co-dopant. The energy transfer mechanism between sensitizer (Bi³⁺) and activator (Eu³⁺) ions has been explained.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Enhanced blue emission and EPR study of LaMgAl11O19:Eu phosphors

Europium doped LaMgAl₁₁O₁₉ phosphor was prepared by the combustion method. The as-prepared and post-treated (1350 °C 10 h 5% H₂+95% N₂) phosphors were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. XRD patterns show that LaMgAl₁₁O₁₉:Eu phosphors have hexagonal structure. FT-IR spectrum exhibits absorption bands corresponding to the stretching vibration of AlO₄ and AlO₆. Morphological studies reveal that this phosphor has faceted plates of varying sizes and shapes. The as-prepared LaMgAl₁₁O₁₉:Eu phosphor consists of both Eu³⁺ and Eu²⁺ ions. The phosphor exhibits a bright blue emission at 450 nm (4f⁶5d→4f⁷ transition of Eu²⁺). On post-treating the phosphor we are able to enhance the blue emission efficiency by 330%. The process was detected from the evolution of excitation, emission and EPR spectra and the results are discussed.