Luminescence of BaSiO<Subscript>3</Subscript> crystals doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript>

The Stokes and anti-Stokes luminescence of undoped and rare-earth-doped (Er³⁺ and Yb³⁺) BaSiO₃ has been studied in the temperature range 78–450 K under excitation at 10–1000 mV. The results indicate that the emission mechanism in BaSiO₃ crystals is hole recombination and that the anti-Stokes luminescence is due to consecutive sensitization; that is, the Yb³⁺ ions in the BaSiO₃ compound act as luminescence sensitizers, and the Er³⁺ ions, as activators.     

Luminescent properties of EuGa2S4:Er3+

We have studied the thermo-and photoluminescence of undoped and Er³⁺-doped EuGa₂S₄ crystals in the temperature range 77–450 K. In thermoluminescence studies, different heating rates and excitation intensities have been used. The results demonstrate that, with increasing heating rate, the intensity of thermoluminescence peaks grows, and the peaks shift to higher temperatures. EuGa₂S₄:Er³⁺ crystals exhibit both Stokes and anti-Stokes luminescence. The mechanisms of these processes are analyzed.     

Luminescence of GaS:Er<Superscript>3+</Superscript> and GaS:Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> layered crystals

Data are presented on the 300-K photoluminescence in GaS crystals doped with Er³⁺ or codoped with Er³⁺ and Yb³⁺. IR excitation (λ_ex = 976 nm) gives rise to anti-Stokes luminescence in GaS:Er³⁺ (0.1 at %) and GaS:Er³⁺,Yb³⁺ (0.1 + 0.1 at %) and leads to an increased intensity of the emission due to the ⁴ I _11/2 → ⁴ I _15/2 transitions. The anti-Stokes luminescence is shown to result from consecutive absorption of two photons by one Er³⁺ ion, and the increased intensity of Er³⁺ luminescence in GaS: Er³⁺,Yb³⁺ is due to energy transfer from Yb³⁺ to Er³⁺.     

Multifunctional anti-stokes Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S-based white phosphors

We have established the key trends in the variation of the intensity of the visible and IR luminescence of (Y_{1 − x − y − z} Yb _x Tm _y Er _z )₂O₂S solid solutions in relation to their composition under laser excitation at λ = 0.940 μm. The results obtained have been used to develop multifunctional anti-Stokes white phosphors with various tinges and a predetermined relative intensities of visible and IR emission bands.     

Anti-stokes luminescence of Y2O3:Er

Diffuse reflectance and spontaneous photoluminescence excitation spectra of the Y₂O₃:Er (10 at % Er) compound have been studied under varied optical pumping conditions. The results demonstrate that the anti-Stokes luminescence of erbium-doped yttrium oxide has high intensity when two different photon energies are used for infrared illumination. The resonance wavelengths of IR photons for two-photon excitation of visible emission in the Y₂O₃:Er phosphor have been determined, and the corresponding electron transitions in erbium-related emission centers have been identified for the Stokes and anti-Stokes luminescence.     

Effect of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> concentration in Bi-containing high-temperature solutions on the luminescence of epitaxial Gd<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> films

Single-crystal gadolinium gallium garnet films have been grown by liquid-phase epitaxy on (111) Gd₃Ga₅O₁₂ substrates from supercooled Bi₂O₃-B₂O₃ fluxed melts at different Gd₂O₃ concentrations. The luminescence spectra of the films have been measured at 10 and 300 K under unmonochromatized synchrotron X-ray excitation and selective UV synchrotron excitation. The Bi³⁺ luminescence is discussed.     

Luminescent properties of Pb<Superscript>2+</Superscript>- and Mn<Superscript>2+</Superscript>-activated CdI<Subscript>2</Subscript> crystals

The luminescent properties of CdI₂, CdI₂:Pb²⁺, CdI₂:Mn²⁺, and CdI₂:Pb²⁺,Mn²⁺) crystals have been studied at temperatures from 85 to 295 K under optical and x-ray excitation. Analysis of new and earlier spectroscopic data suggests that the 560-nm luminescence of CdI₂:Pb²⁺ and CdI₂:(Pb²⁺,Mn²⁺) crystals under excitation on the long-wavelength component of the A absorption band of Pb²⁺ centers is due to Pb²⁺-bound anion excitons. The 640-to 660-nm emission of these crystals is attributable to α centers. The manganese luminescence in the codoped material originates from both intracenter Mn²⁺ excitations and a sensitized process due to energy transfer from the host and Pb²⁺-related centers. The mechanisms of recombination and energy transfer processes in cadmium iodide crystals codoped with Pb²⁺ and Mn²⁺ are discussed.     

Recombination luminescence of activated CaI<Subscript>2</Subscript> crystals

Data are presented on the recombination luminescence of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, and CaI₂:Mn²⁺ crystals grown by the Bridgman-Stockbarger method. It follows from their photostimulated luminescence, roentgenoluminescence, and thermostimulated luminescence spectra that the activation of CaI₂ with Gd²⁺, Eu²⁺, Tl⁺, Pb²⁺, and Mn²⁺ cations, which produce anion defects, leads to the formation of defect complexes which act as electron traps and determine the 90-K photostimulation spectra of the crystals. The observed effect of the nature of the dopant on the photostimulation spectrum indicates that the doped calcium iodide crystals contain near-activator F- and F _A -type electron centers. Under x-ray and optical excitation, the trapping levels in the crystals are filled mainly by charge carriers delocalized from hydrogen- and oxygen-containing centers. The activation increases the decay probability of impurity-bound excitons.     

A new multifunctional phosphor based on yttrium oxysulfide

Novel one-component multifunctional phosphors with the general formula Y_1.975?x Yb_0.025Er _x O₂S:Ti_0.12Mg_0.04 have been prepared via sulfiding of rare-earth, titanium, and magnesium oxides in melts of different sulfur-containing compounds of alkali metals and mineralizers under an SO₂ atmosphere. The phosphors combine a long afterglow with anti-Stokes luminescence and offer unique optical emission properties: yellow luminescence under cw UV excitation with a broadband afterglow around λ_max = 626 nm, predominantly narrow-band green anti-Stokes luminescence with λ_max = 546 nm under 0.96-μm IR excitation, and red anti-Stokes luminescence with λ_max = 670 nm under 1.55-μm IR excitation. Owing to this combination of luminescent properties, the phosphors have considerable potential for practical application.     

The influence of activation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> polycrystalline matrices by Bi<Superscript>3+</Superscript> ions on the luminescence of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

The influence of activation of the Y₂O₃ matrix of the Y₂O₃:Eu³⁺ phosphor by Bi³⁺ ions on the luminescence of Eu³⁺ and Bi³⁺ ions in it and on conditions of the excitation energy transfer to luminescence centers is studied. It is shown that the presence of Bi³⁺ ions leads to the appearance of recombination luminescence with participation of bismuth ions at low concentrations (up to 6–8 at %) of the dominant activator europium and to an increase in the threshold of intrinsic concentration quenching of its luminescence.     

Recombination luminescence of CaI<Subscript>2</Subscript> crystals activated with Eu<Superscript>2+</Superscript>, Gd<Superscript>2+</Superscript>, Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript>

The spectral characteristics of thermostimulated luminescence, steady-state roentgenoluminescence and photostimulated luminescence (PSL) buildup and decay kinetics, and the effect of IR irradiation on the roentgenoluminescence yield and glow curves of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, CaI₂:Mn²⁺, and CaI₂: Pb²⁺, Mn²⁺ crystals grown by the Bridgman-Stockbarger method have been studied in the temperature range 90–295 K. Coupled with earlier data, the present results on the influence of oxygen and hydrogen impurities on the spectral characteristics of CaI₂ indicate that the activation of calcium iodide with Eu²⁺, Gd²⁺, Tl⁺, Pb²⁺, and Mn²⁺ leads to the formation of cation impurity-native defect complexes, which act as carrier traps and are responsible for the thermostimulated luminescence in the range 150–295 K. IR exposure after 90-K x-ray excitation gives rise to flash PSL and influences the thermostimulated luminescence light sum. The nature of the emission and trapping centers involved and the mechanisms of recombination luminescence excitation in the crystals are discussed.     

Upconversion emission of BaTiO<Subscript>3</Subscript>: Er nanocrystals

Here, we report the dopant concentration and pump-power dependence upconversion emission properties of erbium doped BaTiO₃ nanocrystals derived from sol-emulsion-gel method. Green (550 nm) and red (670 nm) upconversion emissions were observed at room temperature from the ⁴ S _3/2 and ⁴ F _9/2 levels of Er³⁺: BaTiO₃ nanocrystals. It is found that at 850 mW of cw excitation power (at 980 nm) the total luminescence was 17130 Cd/m² for 1000°C heated 0.25 mol% Er-doped BaTiO₃ nanocrystals. It is worthwhile to mention that the unusual power-dependent upconversion luminescence (saturation) is observed at higher dopant concentration (2.5 mol%) and high pump power. Our analysis confirms that the depletion of the excited state is responsible for the relevant fluorescence upconversion. We have again confirmed that a twophoton excited state absorption process occurs for all samples.     

Photoluminescence of Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>:Sm<Superscript>2+</Superscript> crystals

The photoluminescence spectra of Ga₂S₃:Sm²⁺ crystals have been measured in a wide temperature range (77–450 K). The results have been used to identify the mechanisms of the luminescence and energy transfer from the host to the rare-earth ion.     

Gamma luminescence of Pr<Superscript>3+</Superscript>- and Ce<Superscript>3+</Superscript>-doped yttrium aluminum garnet crystals

We have studied the gamma luminescence of undoped and Pr³⁺- or Ce³⁺-doped Y₃Al₅O₁₂ crystals gamma-irradiated at 77 and 300 K. The results demonstrate that, depending on temperature, three excitonassisted activator luminescence excitation mechanisms are possible in YAG crystals.     

Effect of BiI<Subscript>3</Subscript> doping on the optical properties of CaI<Subscript>2</Subscript>

The effect of BiI₃ doping on the optical absorption spectra and roentgeno-, photo-, and thermoluminescence of CaI₂ scintillator crystals has been studied in the temperature range 90–295 K. The crystals were grown by the Bridgman-Stockbarger method. Doping of CaI₂ with BiI₃ from the melt gives rise to absorption bands centered at 466, 400, and 350 nm, which can be interpreted as the A, B, and C bands due to electronic transitions from the ¹ S ₀ state to the ³ P ₁, ³ P ₂, and ¹ P ₁ levels of a free Bi³⁺ ion. The absorption band at 270–290 nm is assignable to near-activator excitons. Changes in spectral composition and the reduction in luminescence intensity caused by Bi³⁺ doping of CaI₂ are associated mainly with the reabsorption of the emission from centers characteristic of the host by activator centers. Under x-ray excitation, the spectrum of heavily doped crystals shows, in addition, a weak emission centered around 620 nm, which is probably due to an impurity phase. The light sum of CaI₂:Bi³⁺ under x-ray excitation is small and is due to shallow traps. Upon Bi³⁺ substitution on the cation site of CaI₂, the excess charge of the activator is probably compensated by unintentional O^2? impurity and vacancy pairs near Bi³⁺ centers—one vacancy in a neighboring cation site and the other in a neighboring anion site.     

Flux Growth,Thermal Properties,and Luminescence Spectra of (Er,Yb,Lu)Al<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> Solid Solutions

We have studied phase relations in the pseudoquaternary system LuAl₃(BO₃)₄–(K₂Mo₃O₁₀–Al₂O₃–B₂O₃) in the temperature range 1130 to 900°C. The phase relations were represented in graphical form, as a projection of the formation of solid phases in this range onto the composition triangle at 900°C. Optimal results in terms of high-temperature solution growth have been obtained at 25 wt % LuAl₃(BO₃)₄ in the growth charge. Undoped and erbium–ytterbium codoped LuAl₃(BO₃)₄ (LuAB) single crystals have been grown from high-temperature solutions on “pointlike” seeds. The (Er,Yb):LuAB crystals are similar in thermal properties and luminescence spectra to (Er,Yb):YAl₃(BO₃)₄ and (Er,Yb):GdAl₃(BO₃)₄ crystals and can be used in diode-pumped lasers operating in the nominally eye-safe spectral region 1.5–1.6 μm.     

Cathodo- and photoluminescence of Cu<Subscript>3</Subscript>Ga<Subscript>5</Subscript>Se<Subscript>9</Subscript> single crystals

The cathodo- and photoluminescence spectra of Cu₃Ga₅Se₉ single crystals have been measured at different excitation intensities and temperatures. The results indicate that the radiative recombination of nonequilibrium charge carriers occurs primarily through impurity levels due to anion and cation vacancies. The anion and cation vacancy concentrations can be controlled by thermal and laser anneals.     

Synthesis and luminescent characterization of YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript> phosphors

YAl₃(BO₃)₄:Tb³⁺ phosphors were fabricated by the sol–gel method. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄–⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 nm under UV excitation. It is shown that the 11% of doping concentration of Tb³⁺ ions in YAl₃(BO₃)₄:Tb³⁺ phosphors is optimum.     

Luminescence Study of LiY<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript>x</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The luminescence spectra of LiY_{1 − x} Eu_x(MoO₄)₂ (x = 0.0005, 0.001, 0.01, 0.05, 0.1, 0.5, 1) scheelite solid solutions are measured under laser excitation at 337.1 nm. The effect of Eu³⁺ concentration on the luminescence behavior of the solid solutions is examined. The highest integrated emission intensity is offered by LiY_0.5Eu_0.5(MoO₄)₂. Eu³⁺ substitution for Y³⁺ has no effect on the symmetry of the emission centers involved. Eu³⁺ is shown to occupy only one site in the structure of the solid solutions. X-ray diffraction and luminescence data indicate that all of the solid solutions have an undistorted scheelite structure.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 871–875.Original Russian Text Copyright © 2005 by Zaushitsyn, Mikhailin, Romanenko, Khaikina, Basovich, Morozov, Lazoryak.     

Thermo-and photostimulated luminescence of CaI<Subscript>2</Subscript>-based crystals

We systematize earlier and new data on the effect of oxygen and hydrogen impurities on recombination processes in CaI₂ crystals by jointly examining their roentgeno-, thermo-, and photostimulated luminescence spectra. The 90-K emission spectra of CaI₂ crystals are shown to consist of at least five bands. The 395-nm emission is assumed to be due to radiative decay of (HI)* heteronuclear excitons. The 520-nm luminescence is attributable to iodine-vacancy-bound anion excitons. The thermostimulated luminescence peaks observed in the temperature range 90–150 K are due to the thermal dissociation of V _k and H hole centers. The 90-K photostimulated luminescence of CaI₂-based crystals is shown to be excited in the electronic stage of the recombination process.