Luminescence and Optical-Memory model of SrAl2O4:Eu2+,Dy3+ and Sr4Al14O25:Eu2+,Dy3+

The photoluminescence, luminescence excitation, and phosphorescence spectra of SrAl²O⁴:Eu²⁺,Dy³⁺ and Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ powder phosphors have been studied in detail at 80 and 300 K. A conceptual model is proposed for strontium-aluminate-based optical memory.     

Luminescence properties for the high-pressure polymorphs of CaSiO3:Pb2+ and SrSiO3:Pb2+

High-pressure phases of CaSiO₃:Pb²⁺ and SrSiO₃:Pb²⁺ phosphors were synthesized at 40–55 kbar and 1000°C, $\text{viz}$. δ-CaSiO₃:Pb²⁺, δ-SrSiO₃:Pb²⁺, and δ′-SrSiO₃:Pb²⁺, and their luminescence properties were investigated. Among them, δ-CaSiO₃:Pb²⁺ was found to give a strong violet-blue emission ($\text{ca}$. 341 nm) as well as β-CaSiO₃:Pb²⁺ (an atmospheric phase), and the emission intensity of SrSiO₃:Pb²⁺ drastically increased when the host lattice transformed into high-pressure phases (δ and δ′ forms). These results were discussed by considering their structures and quenching temperatures of luminescences.     

Synthesis and properties of liquid luminophores POCl3-SbCl5-Nd3+ and POCl3-SbCl5-235UO 22+

Luminophores POCl₃-SbCl₅-Nd³⁺ with Nd concentration of up to 0.8 M and Nd³⁺ luminescence lifetime of up to 220 μs and POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ with uranyl concentration of up to 0.16 M were prepared. It was found that stable liquids POCl₃-SbCl₅-Nd³⁺ and POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ can be obtained when salt crystal hydrates are used or water is added to anhydrous Nd and U(VI) compounds. The SbCl₅ content should be 1 ≤ [SbCl₅]/[Nd³⁺] ≤ 2 for the POCl₃-SbCl₅-Nd³⁺ system and [SbCl₅]/[UO ₂ ²⁺ ] > 3 for the POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ system. Based on the solubility of Nd and U(VI) compounds in the POCl₃-SbCl₅ solvent and spectral-luminescence properties of Nd³⁺ and UO ₂ ²⁺ in the luminophores obtained, the following compositions of the complexes formed were suggested: Nd(PO₂Cl₂)_3−y (SbCl_y)_y · xPOCl₃, where y = 1, 2, and 3, and UO₂(PO₂Cl₂)(SbCl₆) · xPOCl₃. Original Russian Text ? G.V. Tikhonov, S.V. Kiselev, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 6, pp. 524–528.     

Crystalline spectra of Pr3+ in CdF2

We report the first observation of line structure in the cathodoluminescence spectrum of cadmium fluoride crystals doped with trivalent praseodymium ions. CdF₂:Pr shows luminescence from ³P₁, ³P₀ and ¹D₂ to low lying levels of Pr³⁺ (³H, ³F). Anomalous temperature dependence of the emission decay measurements was observed. The decay-time constants decreased when the temperature was lowered within the range 300°–77°K. Possible mechanism for this phenomena is discussed.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

On the luminescence of Ti4+ In Mg5SnB2O10 and Mg3ZrB2O8

The following new compounds are reported: Mg₅TiB₂O₁₀ (ludwigite structure), Mg₅SnB₂O₁₀ (orthopinakiolite structure) and Mg₃ZrB₂O₈ (warwickite structure). The luminescences of the systems Mg₅(Sn,Tl)B₂O₁₀ and Mg₃(Zr,Ti)B₂O₈ were measured. The results are discussed in terms of delocalization in clusters of titanate octahedra. A general scheme for the luminescence of Ti⁴⁺-activated compositions is given. The composition Mg₅SnB₂O₁₀: Ti is a very efficient luminescent material for titanium concentrations below some 20 mole percent.     

Luminescence de Ce3+ dans les poly et metaphosphates mixtes xM2O.Ce2O3. (x + 3)P2O5, x = 1, 2

Several binary poly- and meta-phosphates of cerium and monovalent cations, xM₂O.Ce₂O₃. (x + 3)P₂O₅, have been investigated. We describe their chemical preparation and give, for the first time, spectroscopic characteristics of the Ce³⁺ luminescence in this host lattice. Excitation spectrum of these compounds produce four or five bands in the UV spectra. Emission spectra present two strong bands in the wavelength range 310 – 452 nm. We determine for each one of these compounds two lifetimes: τ₁ = 5–22 ns and τ₂ = 25–67 ns. Besides their good optical properties, xM₂O.Ce₂O₃. (x + 3)P₂O₅ are not hygroscopic and resist thermal effects.     

Synthesis and Spectral Study of New Complexes of Eu3+, Am3+, and Cm3+ with GaMo6O18(OH)

Complexing of Am(III) with GaMo₆O₁₈(OH) ₆ ³⁻ polyanion in an aqueous solution was studied. The stability constant β of the resulting complex was estimated at 100–150 l mol⁻¹ at pH 4.0. Crystalline complexes of Eu(III) and Gd(III) [doped with 0.5–1.5% Cm(III) ion] with GaMo₆O₁₈(OH) ₆ ³⁻ polyanion were synthesized from H₂O and D₂O solutions. The luminescence spectra and lifetime were measured for the compounds at T = 295 and 77 K. The luminescence characteristics of the Eu(III) complex proved to be virtually identical to those of the previously synthesized compound EuAlMo₆O₁₈(OH)₆·xH₂O. This also concerns the luminescence of Cm³⁺-doped GdGaMo₆O₁₈(OH)₆·xH₂O complex. The results suggest identical structures of the new compounds and complexes of lanthanides with the AlMo₆O₁₈(OH) ₆ ³⁻ anion. __________ Translated from Radiokhimiya, Vol. 47, No. 6, 2005, pp. 507–511. Original Russian Text Copyright ? 2005 by Yusov, Fedoseev.     

Luminescence enhancement of Y2O3:Eu and Y2SiO5:Ce,Tb core particles with SiO2 shells

This paper reports on the luminescence and microstructural features of oxide nano-crystalline (Y₂O₃:Eu³⁺) and submicron-sized (Y₂SiO₅:Ce³⁺,Tb³⁺) phosphor cores, produced by two different synthesis techniques, and subsequently coated by an inert shell of SiO₂ using a sol-gel process. The shells mitigate the detrimental effect of the phosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20-90%, depending on the core composition and shell thickness. For Y₂O₃:Eu³⁺, uniformly shaped, narrow particle size distribution core/shell particles were successfully fabricated. The photoluminescence emission intensity of core nanoparticles increased with increasing Eu³⁺ activator concentration and the luminescence emission intensity of the core/shell particles was 20-50% higher than that of the core particles alone. For Y₂SiO₅:Ce³⁺,Tb³⁺, the core/shell particles showed enhancement of the luminescence emission intensity of 35-90% that of the core particles, depending on the SiO₂ shell thickness.     

Luminescent properties of GdAl3(BO3)4:Ln3+ (Ln3+:Eu3+, Tb3+, Dy3+) nano-phosphors

GdAl₃(BO₃)₄:Ln³⁺ (Ln³⁺:Eu³⁺, Tb³⁺, Dy³⁺) nano-phosphors were prepared by sol–gel method. The structure properties of the phosphors are characterized by XRD, and GdAl₃(BO₃)₄:Ln³⁺ nano-phosphors have average sizes around 40 nm. The doping concentrations of Eu³⁺, Tb³⁺ and Dy³⁺ ions in GdAl₃(BO₃)₄ nano-phosphors are from 1 to 9 mol% for Eu³⁺ ions, from 2 to 12 mol% for Tb³⁺ ions and from 1 to 5 mol% for Dy³⁺ ions, respectively. The luminescent properties of rare-earth ions doped GdAl₃(BO₃)₄ nano-phosphors are analyzed by the photoluminescence spectra, which prime doping concentration of Eu³⁺, Tb³⁺, and Dy³⁺ ions are at 5, 12 and 3 mol%, respectively. The energy transfers in the luminescent processes of rare-earth ions doped GdAl₃(BO₃)₄ nano-phosphors are discussed.     

Growth and luminescent properties of Lu2SiO5 and Lu2SiO5:Ce single crystalline films

Single crystalline films (SCF) of Lu₂SiO₅ (LSO) and Lu₂SiO₅:Ce (LSO:Ce) silicates with thickness of 2.5-15 μm were crystallized by liquid phase epitaxy method onto undoped LSO substrates from melt-solution based on PbO-B₂O₃ flux. The scintillation and luminescence properties of LSO:Ce SCF were compared with the properties of LSO:Ce single crystal. The peculiarities of luminescence properties of LSO:Ce SCF in comparison with crystal analog can be due to different distribution of Ce³⁺ over the Lu1 and Lu2 positions of LSO host and are further influenced by Pb²⁺ flux-originated contamination.     

High pressure luminescence and time resolved spectra of La2Be2O5:Pr

We present luminescence, luminescence excitation and luminescence time resolved spectra of La₂Be₂O₅:Pr³⁺ system. We used high pressure spectroscopy approaches, with high pressure applied in diamond anvil cell (DAC) and sapphire anvil cell (SAC), for detailed analysis of luminescence related to the 4f5d → 4f² and 4f² → 4f² transitions. We present effect of up-converted luminescence related to 4f5d → 4f² transition excited with 488 nm. We also discussed possibility of existence of praseodymium trapped exciton (PTE) states in La₂Be₂O₅:Pr³⁺ system. Lack of the PTE is attributed to high quantity of bulk modulus of this material.     

Influence of doping Nb5+ and Mn2+ on the PTCR effects of Ba0.92Ca0.05(Bi0.5Na0.5)0.03TiO3 ceramics

As a positive temperature coefficient of resistivity (PTCR) material, Ba_0.92Ca_0.05(Bi_0.5Na_0.5)_0.03TiO₃ ceramics with donor doping of Nb⁵⁺ and acceptor doping of Mn²⁺ were prepared by a conventional mixed oxide method. The influence of contents of Nb⁵⁺ and Mn²⁺ on the microstructure and PTCR characteristics of Ba_0.92Ca_0.05(Bi_0.5Na_0.5)_0.03TiO₃ ceramics sintered at 1,360°C for 2 h was investigated. The result showed that the Curie temperature (T _c) was shifted to a lower temperature with increasing of the content of Nb⁵⁺ and the resistance jump (ρ_max/ρ_min) was enhanced with doping of Mn²⁺. The grain size of ceramic sample decreased with increasing of contents of donor Nb⁵⁺ and acceptor Mn²⁺. The Ba_0.92Ca_0.05(Bi_0.5Na_0.5)_0.03TiO₃ ceramic with 0.4 mol%Nb⁵⁺ and 0.04 mol%Mn²⁺ exhibited a low ρ_RT of 5.0 × 102 Ω cm, a typical PTCR effect of ρ_max/ρ_min > 10³, and a T _c of 158°C.     

Optically rewritable Bragg gratings in Mn2+ doped RbCdF3

Optical absorption, optically stimulated luminescence, and thermo-luminescence measurements have been made on RbCdF₃:Mn²⁺ single crystals with the aim of characterizing this compound for holographic storage. We show that there are stable traps that are filled after deep ultra-violet irradiation (<270 nm) and they can be emptied after ∼365 nm irradiation. The photo-induced changes in the optical properties can be used to create optically rewritable Bragg gratings in these crystals.     

Effect of Y3+ codoping on luminescence decays of the 4I13/2 level in Er3+-doped Al2O3 powders prepared by a sol-gel method

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er³⁺- and 0–20 mol.% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er³⁺-doped Al₂O₃ by Y³⁺ codoping. For the 0.1 mol.% Er³⁺-Y³⁺-codoped Al₂O₃ powders, the measured lifetime of Er³⁺ gradually increases with increasing Y³⁺ concentration. Consequently, codoping with 20 mol.% Y³⁺ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er³⁺ concentrations in the Al₂O₃ powders, the radiative lifetime of both the Er³⁺-doped and the Er³⁺-Y³⁺-codoped Al₂O₃ powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y³⁺ codoping does not change the-OH content in the Er³⁺-Y³⁺-codoped Al₂O₃ powders. The prolonged luminescence lifetime of the ⁴I_13/2 level of Er³⁺ in Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping is ascribed to the decrease in the energy transfer rate between the Er³⁺ ions and the Er³⁺ and -OH, respectively, due to the suppressed interaction between Er³⁺ ions.     

Energy transfer from Eu2+ to trivalent rare earth ions in BaY2F8

An efficient energy transfer from divalent europium to trivalent rare earth ions appears in the luminescence spectrum of BaY₂F₈ when it is simultaneously doped with Eu²⁺ and Ln³⁺ ions (Ln = Tb, Ho, Er) as a consequence of a f-f emission of Eu²⁺.     

Novel blue-emitting Sr3Ga2O5Cl2:Eu phosphor for UV-pumped white LEDs

A novel blue-emitting Sr₃Ga₂O₅Cl₂:Eu²⁺ phosphor has been synthesized by a two-step solid-state reaction. The luminescence properties have been investigated by photoluminescence (PL) spectra, and temperature-dependent PL spectra. It shows an efficient broad absorption band around 400 nm, which matches well with the commercial near-ultraviolet light-emitting chips, and an efficient blue emission. It shows a higher thermal quenching temperature than that of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor. Sr₃Ga₂O₅Cl₂:Eu²⁺ phosphor is a promising blue-emitting component for UV chip excited white light-emitting-diodes.     

Crystal structure and fluorescence spectrum of 3Y2O3, WO3: Eu3+

A structural study of the rhombohedral compound 3Y₂O₃, WO₃ doped with Europium was carried out. The fluorescence spectrum of Eu³⁺ was measured in the frequency range 12500–25000 cm^?1. Transitions from the excited state 5D₀ to the Stark components of the five lowest 7F_J (J=0,1,2,3,4) states were observed. The analysis revealed that the rare earth ion is within a crystal field of C₁ symmetry. We found values for the B^k_q parameters which give a good agreement between the observed and calculated levels.     

The luminescent enhancement of LaPO4:Ce3+,Tb3+ nano phosphors by radial aggregation

The rare earth nano phosphors can meet the challenging demand for new functional devices but their luminescence is always poor. Here we report on a simple method to prepare uniform LaPO₄:Ce³⁺,Tb³⁺ sphere-like nano aggregates from the precipitated nano phosphor crystallites without using any additive. The spontaneous aggregation is induced and controlled only by the suspension pH conditions. It is found that the 100 nm spherical aggregates can significantly improve the green emissions of the LaPO₄:Ce³⁺,Tb³⁺ nano particles. The intensity of the aggregates can be about 10 times as that of the 80 nm-sized individual ones. This study may provide a useful yet convenient strategy in the improvement and application of nano phosphors.     

On the number of V4+ ions in V2O5-MoO3 solid solutions

The nesults of magnetic and thermognavimetnic studies on V₂O₅-MoO₃ solid solutions are presented. We determine the number of V⁴⁺ ions induced by the presence of Mo⁶⁺ ones. The ratio between the number of V⁴⁺ ions and those of Mo⁶⁺ decreases by increasing the MoO₃ content. Finally, this behaviour is analysed.