Europium doped strontium borate glasses and their optical properties

Optical absorption and luminescence spectra of europium doped strontium borate glasses prepared in different conditions are studied. It is found that the percentage of Eu³⁺ ions varies from 100 to 30% being controlled by the conditions of preparation. The mechanism, favoring reduction of europium to Eu²⁺ state in polycrystalline strontium tetraborate, is much weaker in glasses of the same composition. In samples containing mixed valence europium at densities of 8×10²⁰ cm⁻³, the efficient transfer of optical excitation from Eu³⁺ to Eu²⁺, suppressing the Eu³⁺ luminescence, has been found. The most reliable way of monitoring the percentage of europium ions in different valences for strontium borate glasses is the measuring of absorption at f-f transition ⁷F₀→⁵D₂ of Eu³⁺.     

Luminescence-spectral properties and structure of optical centers in Eu-and Ce-Eu-containing quartz gel-glasses

Eu-and Ce-Eu-containing quartz glasses obtained by a direct sol-gel-glass transition are investigated. It is discovered that the conversion of a xerogel into a glass leads to lowering of the symmetry of the Eu³⁺ optical centers from hexagonal to orthorhombic and a many-fold increase in the efficiency of the excitation of their luminescence through the charge-transfer band. In the co-activated glasses, the distortion of these centers is enhanced, and compound Ce⁴⁺-Eu³⁺ centers appear, in which the Eu(III) oxo complexes are characterized by cubic symmetry and by sensitization of the luminescence of the Eu³⁺ ions by photoreduced (Ce⁴⁺)⁻ ions. Crystal-field theory shows that the coordination number of the cation in such oxo complexes is equal to 8. It is established that similar structural formations exist in annealed xerogels, but they are manifested spectroscopically only upon low-temperature shortening of the interatomic distances, as a result of which the sensitization indicated becomes possible. Fiz. Tverd. Tela (St. Petersburg) 41, 229–234 (February 1999) Deceased.     

Optical Properties of Rare Earth Doped Transparent Oxyfluoride Glass Ceramics

Optical properties of Eu^3? ions in oxyfluoride glasses and glass ceramics doped with low concentration (0.1 mol%) have been analysed and compared with previous results for high concentrated samples (2.5 mol%). The Eu^3? ions in the low dopant concentration glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonons energy than in the precursor glasses. Fluorescence line narrowing measurements indicate the presence of two main fluoride site distributions for the Eu^3? ions in these low concentrated glass ceramics.     

Optical absorption and photoluminescence studies of Eu-doped phosphate and fluorophosphate glasses

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 C_2v 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→⁷F_J (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→⁷F_J 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.     

Luminescence Properties of Dual Valence Eu Doped Nano-crystalline BaF2 Embedded Glass-ceramics and Observation of Eu2+ → Eu3+ Energy Transfer

Europium doped glass-ceramics containing BaF₂ nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF₂ nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm⁻¹ has been demonstrated from the emission spectra of Eu³⁺ ions showing the transitions from upper excitation states ⁵D_J (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu³⁺) ions to divalent (Eu²⁺) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu²⁺ to Eu³⁺ ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu³⁺ to Eu²⁺ under normal air atmospheric condition has been observed in a BaF₂ containing oxyfluoride glass-ceramics system.     

Measurement of optical dephasing of Eu3+ and Pr3+ doped silicate glasses by spectral holeburning

Long-lived spectral holeburning has been observed in Eu³⁺ and Pr³⁺ doped silicate glasses, and used to measure homogeneous linewidths (φ_h). In the case of Eu³⁺, holes are burned by optical pumping of nuclear quadrupole levels, and our low temperature measurement of φ_h shows that the previously determined T^1.8 temperature dependence holds down to at least 1.6 K. On the other hand, in Pr³⁺ doped glass, holes are burned by optically induced local lattice rearrangements. In contrast to previously studied inorganic glasses, we find a linear temperature dependence of φ_h for the ³H₄ ? ¹D₂ transition from 1.6 K to 20 K. This was confirmed by picosecond accumulated grating photon echoes. Current theories of dephasing in glasses do not predict these temperature dependences. Holeburning has also been observed in Pr³⁺ doped BeF₂ and phosphate glasses and Nd³⁺ doped silicate glass and thus appears to be a rather general phenomenon in inorganic glasses, as has been found for molecules in organic glasses.     

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.     

Luminescent features of sol–gel derived rare-earth multi-doped oxyfluoride nano-structured phosphors for white LED application

Rare-earth doped oxyfluoride 75SiO₂:25PbF₂ nano-structured phosphors for white-light-emitting diodes were synthesized by thermal treatment of precursor sol–gel derived glasses. Room temperature luminescence features of Eu³⁺, Sm³⁺, Tb³⁺, Eu³⁺/Tb³⁺, and Sm³⁺/Tb³⁺ ions incorporated into low-phonon-energy PbF₂ nanocrystals dispersed in the aluminosilicate glass matrix and excited with UV light emitting diode were investigated. The luminescence spectra exhibited strong emission signals in the red (600, 610, 625, and 646 nm), green (548 and 560 nm), and blue (485 nm) wavelength regions. White-light emission was observed in Sm/Tb and Eu/Tb double-doped activated phosphors employing UV-LED excitation at 395 nm. The dependence of the luminescence emission intensities upon annealing temperature and rare-earth concentration was also examined. The results indicated that there exist optimum annealing temperature and activator ion concentration in order to obtain intense visible emission light with high color rendering index. The study suggests that the nanocomposite phosphor based upon 75SiO₂:25PbF₂ host herein reported is a promising contender for white-light LED applications.     

Eu3+离子在微晶玻璃研究中的探针作用

制备出单掺Eu³⁺离子的氟氧化物玻璃陶瓷系列样品，利用Eu³⁺离子作为荧光探针，通过热处理前后Eu³⁺离子发射光谱中电偶极子跃迁与磁偶极子跃迁强度比值的变化表征在玻璃材料中微晶是否形成，分析了Eu³⁺离子荧光发射谱中电偶极子跃迁与晶体场对称性的关系，进一步表征了稀土离子所处微晶晶格场的变化. 关键词： 微晶玻璃 探针 3+离子')" href="#">Eu³⁺离子     

Optical spectra of triply-charged rare-earth ions in polycrystalline corundum

Solid samples of polycrystalline corundum α-Al₂O₃ activated by triply-charged rare-earth ions RE³⁺ (R=Eu³⁺, Er³⁺, Pr³⁺) were synthesized by the sol-gel technology. Characteristic narrow-line optical absorption and luminescence spectra produced by intraconfigurational 4f-4f transitions in RE³⁺ ions have been measured. RE³⁺ ions have been established to form one dominant type of optical centers in the corundum matrix, and the energy diagram of Eu³⁺ and Er³⁺ Stark levels in corundum has been determined. Fiz. Tverd. Tela (St. Petersburg) 40, 1442–1449 (August 1998)     

Concentration dependent Eu3+ doped boro-tellurite glasses—Structural and optical investigations

Eu³⁺ doped boro-tellurite glasses with the chemical composition (40?x)B₂O₃+30TeO₂+15MgO+15K₂O+xEu₂O₃ (where x=0.01, 0.1, 1, 2 and 3 wt%) have been prepared by following the conventional melt quenching technique. Structural and optical behavior of the prepared Eu³⁺ doped boro-tellurite glasses were studied and compared with reported literature. The XRD pattern confirms the amorphous nature and the FTIR spectral studies explore the presence of BO stretching vibrations, O₃BOBO₃ bond bending vibrations along with the bending vibration of TeOTe linkages in the prepared glasses. Through the optical absorption spectra, bonding parameters ($\overline{\beta },\delta$) were calculated to identify the ionic/covalent nature of the glasses. Judd–Ofelt (JO) parameters have been calculated from the luminescence spectral measurements. The JO parameters (Ω_λ, λ=2, 4 and 6) were used to calculate the radiative properties like transition probability (A), stimulated emission cross-section (${\sigma }_P^E$), radiative lifetime (τ_rad), and branching ratios (β_R) for the ⁵D₀→⁷F_J (J=0, 1, 2, 3 and 4) emission transitions of the Eu³⁺ ions. The local site symmetry around the Eu³⁺ ions were calculated through the luminescence intensity ratio (R) of the ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁ transitions. The experimental lifetime of the ⁵D₀ level in the Eu³⁺ doped boro-tellurite glasses has also been calculated and compared with similar Eu³⁺ glasses. The lifetime of the ⁵D₀ level is found to be less than the reported glasses and it may be due to the presence of OH^? groups in the prepared glasses. The Optical band gap (E_opt), band tailing parameter (B) and the Urbach energy (ΔE) values of the prepared glasses were calculated from the absorption spectral measurements and the results were discussed and reported.     

Optical properties of Eu3+ and Ho3+ in fluoride glasses

Conclusions Emission and excitation spectra as well as the lifetime and the Judd-Ofelt parameters were determined for the different sites occupied by Eu³⁺ ions in a fluorzirconate glass. As has been observed in borate glasses, the Ω₄ parameter increases with the excitation energy of the⁷F₀→⁵D₀ transition, while Ω₄ is nearly constant [5, 6]. These parameters are lower than in borate glasses by a factor of close to 3. The optical properties of the Eu³⁺ ions in the studied glass appear to be dominated by only one class of sites; however, the presence of a second class of sites is possible. Efficient energy transfer from Eu³⁺ to Ho³⁺ is observed, but the energy transfer parameter does not depend appreciably on the excitation wavelength. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 4, pp. 185–190, July–August, 1995.     

Luminescence of molecular silver clusters in oxyfluoride glasses

Luminescence spectra of silver-containing oxyfluoride glasses have been investigated in the excitation spectral range of 360–480 nm. Analysis of the luminescence spectra shows that silver in oxyfluoride glasses that contain no strong reducers and were subjected to heat treatment affecting redox processes exists in the form of neutral atoms and neutral molecular Ag₂, Ag₃, and Ag₄ clusters.     

Synthesis and Spectral Study of Several Solid M3[Eu(2,6-Pyridinedicarboxylate)3] Salts (M=Li+, Na+, K+, Rb+, Cs+, NH4 +, and Pyridinium+)

Abstract

Salts of the [Eu(2,6-pyridinedicarboxylate)₃]^3- complex anion and various monovalent inorganic and organic counterions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺, and pyridinium⁺) have been synthesized and studied by emission spectroscopy. The Eu³⁺ ion emission spectra exhibited by these salts have been observed with high resolution (less than 1.0 cm^?1) and at low temperature (77 K). The emission spectra of these compounds indicate that changing the attached counterion does not affect the site symmetry observed by the europium ion beyond slight distortions indicated by small shifts in the energies of the Eu³⁺ electronic levels.     

Blue light emission from Eu ions in sol-gel-derived Al2O3-SiO2 glasses

Blue light-emitting glasses were successfully prepared by doping Eu²⁺ ions in the system Al₂O₃-SiO₂. The Al₂O₃-SiO₂ glasses doped with Eu³⁺ ions were synthesized using a sol-gel method, followed by heating in hydrogen gas atmosphere to reduce into the Eu²⁺ ions. The obtained glasses exhibited emission spectra with peak at ∼450 nm due to 4f⁶5d→4f⁷ (⁸S_7/2) transition, the intensities of which strongly changed depending on their glass composition and heating conditions. The emission quantum efficiency of 48% was achieved by heating the glass with the ratio of Al³⁺ to Eu³⁺ at about 6 at 1000 °C in hydrogen gas atmosphere. It was found that the Al₂O₃-SiO₂ glasses were appropriate not only for homogeneously doping the Eu³⁺ ions in glass structure but also reducing to Eu²⁺ ions, resulting in enhanced blue light-emission properties.     

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.     

Eu luminescence in tellurite glasses with gold nanostructures

Luminescence properties of Eu³⁺ doped TeO₂-PbO-GeO₂ glasses containing gold nanoparticles (NPs) were investigated. The emission spectra of the samples exhibited enhancement of Eu³⁺ luminescence due to the presence of gold NPs. The emission at 614 nm, due to the Eu³⁺ hypersensitive transition ⁵D₀-⁷F₂, is much influenced by the gold NPs and increases by ≈100% for samples heat-treated at 350 °C during 41 h.     

Luminescence characteristics of energy transfer between Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> in NaMgPO<Subscript>4</Subscript> phosphor

Powder samples of NaMgPO₄ doped with Eu²⁺ and Ce³⁺ were prepared and their photoluminescence spectra were systemically studied. Energy transfer from Ce³⁺ to Eu²⁺ in NaMgPO₄ phosphor was observed by investigating the optical properties from photoluminescence spectra in Eu²⁺ or Ce³⁺ singly doped and Eu²⁺–Ce³⁺ codoped sodium magnesium orthophosphates, NaMgPO₄. The enhancement of UV excitation is attributed to energy transfer from Ce³⁺ to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺–Eu²⁺ codoped NaMgPO₄ phosphors in which Eu²⁺ can be efficiently excited by 390 nm are potential candidates for phosphor-converted LEDs.     

Excitation and luminescence of rare earth-doped lead phosphate glasses

Excitation and luminescence properties of Eu³⁺, Tb³⁺ and Er³⁺ ions in lead phosphate glasses have been studied. From excitation spectra of Eu³⁺ ions, the electron–phonon coupling strength and phonon energy of the glass host were calculated and compared to that obtained by Raman spectroscopy. Main intense and long-lived luminescence bands are related to the ⁵D₀–⁷F₂ (red) transition of Eu³⁺, the ⁵D₄–⁷F₅ (green) transition of Tb³⁺ and the ⁴I_13/2–⁴I_15/2 (near-infrared) transition of Er³⁺. The critical transfer distances, the donor–acceptor interaction parameters and the energy transfer probabilities were calculated using the fitting of the luminescence decay curves from ⁵D₀ (Eu³⁺), ⁵D₄ (Tb³⁺) and ⁴I_13/2 (Er³⁺) excited states. The energy transfer probabilities for Eu³⁺ (⁵D₀), Tb³⁺ (⁵D₄) and Er³⁺ (⁴I_13/2) are relatively small, which indicates low self-quenching luminescence of rare earth ions in lead phosphate glasses.     

Optical properties of Eu-doped zinc borate glasses

Photoluminescence, absorption and optical excitation spectra of undoped and Eu³⁺-doped binary zinc borate glasses of varied composition prepared by the melt quenching technique in air atmosphere were investigated. From photoluminescence measurements it was found that growing Eu³⁺ concentration leads to gradual disappearance of the broadband glass emission in the near-UV spectral range, while the red Eu³⁺ emission at 613 nm shows a considerable increase. This result together with excitation spectra suggests that the Eu³⁺ ions are excited via energy transfer from the initially excited glassy host. The glass composition strongly affects the position of the excitation maximum in the UV energy range.