Photo-and X-ray luminescence spectra of CsPbX3 microcrystals dispersed in a PbX2 (X=Cl, Br) matrix

The CsPbX₃ (X=Cl, Br) microcrystals are obtained in a PbX₂ (X=Cl, Br) matrix doped with Cs ions (C _Cs=0.1–1 mol %). Spectral and kinetic parameters of the intrinsic luminescence of the CsPbX₃ single crystals are presented. For the CsPbCl₃ microcrystals, a quantum-confinement effect is detected, which reveals itself as a decrease in the lifetime of the free exciton luminescence. A mechanism of formation of a CsPbX₃ microcrystal in a PbX₂ matrix is proposed.     

X-ray luminescence of Pb-containing microcrystals dispersed in the CsCl Matrix

The process of complexing in CsCl crystals in activating them with lead haloids PbX₂ (X=Cl, Br, I) (C_{PbX 2}=1 mole %) is investigated. The formation of CsPbCl₃ and Cs₄PbCl₆ microcrystals that are dispersed in the CsCl matrix is recorded. The luminescence-kinetic characteristics of the indicated microcrystals and single Pb²⁺v _c ⁻ centers are investigated. It is noted that the formation of the CsPbCl₃ and Cs₄PbCl₆ microcrystals is hindered as the radius of the anion of the lead haloid PbX₂ (X=Cl, Br, I) increases. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 480–482, July–August, 2000.     

Luminescence kinetics characteristics of lead-containing aggregates dispersed in Rb0.95Cs0.05Cl solid state solution

The relaxation of the electron excitations in an insulating matrix such as the Rb_0.95Cs_0.05Cl solid solution containing CsPbCl₃ nanocrystals and single lead centers is studied. Modification of the spectral kinetic parameters of the CsPbCl₃ nanocrystals due to the quantum confinement is explored. Mechanism of the energy transfer from matrix to the nanocrystals is established. The luminescence of the Rb_0.95Cs_0.05C–Pb crystal is characterised by means of measurements with subnanosecond time resolution under synchrotron radiation excitation in the energy range of 3.7–20 eV at T=10 K.     

Luminescence properties of LaBr<Subscript>3</Subscript>:Ce microcrystals dispersed in NaBr matrix

The formation of LaBr₃-Ce microcrystals 1–10 μm in size dispersed in a NaBr matrix has been revealed in a NaBr-LaBr₃(1%)-CeBr₃(0.05%) crystal by electron microprobe analysis and luminescence spectroscopy. The spectral-luminescence and luminescence-kinetic characteristics of the NaBr-LaBr₃(1%)-CeBr₃(0.05%) crystal under optical and X-ray excitations have been investigated. The spectral-luminescence properties of LaBr₃:Ce microcrystals dispersed in an NaBr matrix are identical to those in the bulk analogs. The mechanisms of energy transfer to Ce³⁺ ions during crystal excitation in the ranges of transparency and fundamental absorption of NaBr and LaBr₃ matrices are discussed.     

Growth and spectroscopic studies of NaLa(MoO4)2:Tm3+ crystals: A new promising laser material

Single crystals of scheelite-like disordered double molybdate NaLa(MoO₄)₂ doped with thulium ions with dopant concentrations of 3.0 × 10¹⁹ and 1.2 × 10²⁰ cm^?3 are grown by the Czochralski method. Spectral and luminescent studies of crystals grown are performed in wavelength ranges of 800 nm (the transitions ³ H ₆?³ H ₄) and 2 μm (the transitions ³ H ₆?³ F ₄), including the measurements of the polarized absorption and luminescence spectra of these crystals and the decay kinetics of their excited states. A model that satisfactorily describes the decay kinetics of the luminescence from the ³ H ₄ level taking into account cross-relaxation interactions is proposed. The prospects for the use of these crystals as active media in two-micrometer solid-state lasers are discussed.     

Luminescence of SrX 2 microcrystals (X = Cl,I) activated with Eu2+ ions and dispersed in a NaI matrix

Luminescence spectroscopy has been used to determine the parameters of NaI-SrI₂-Eu, NaI-SrCl₂-Eu, and NaI-BaI₂-Eu compounds in the energy range of 3.7–18 eV at 10 and 295 K and investigate the phase formation in these crystalline systems. The NaI-SrI₂(1 mol %)-Eu(0.02 mol %) crystalline system has revealed formation of SrI₂ microcrystals activated with europium ions and dispersed in the NaI matrix. Formation of SrCl₂-Eu²⁺ microcrystals dispersed in a NaI matrix is observed for NaI-SrCl₂(1 mol %)-Eu(0.02 mol %) crystalline system. The mechanisms of aggregation of impurity ions and specific features of luminescence excitation for europium ions in dispersed microcrystals are discussed.     

Time-Resolved Spectroscopy in ZnWo4 and ZnWO4:Fe

Time-resolved luminescence and absorption of ZnWO⁴ and ZnWO₄:Fe have been studied. The fast decaying luminescence at ～1.7eV is attributed to either Fe^2? or a Fe^3? related center. The two observed stages in luminescence decay kinetics under ionising radiation are suggested to be due to two types of self-trapped excitons.     

Ionic conduction of the perovskite-type halides

The ionic conduction in the perovskite-type halides, CsPbCl₃, CsPbCl₃ and KMnCl₃, was studied. Measurements were made of ac conductivity at temperatures from 150°C to the melting point, and of ionic transport number using the Tubandt, EMF and ion-blocking methods. The effects of impurity doping on the ionic conductivity of CsPbCl₃ were also studied using the samples of composition, CsPb_0.99M_0.01Cl_2.99 (M = Li, Na, K, Ag). It was concluded that these materials are halide-ion condcutors. The ionic conductivities of CsPbCl₃ and CsPbBr₃ are close to those of the well known halide-ion conductors, PbCl₂ and PbBr₂. The ionic transport numbers were found to be > 0.9 for CsPbCl₃ and CsPbBr₃, and about 0.99 for KMnCl₃. The conduction was considered to be caused by the migration of halide-ion vacancies V_X (X = Cl, Br). The activation energies for the migration of V_X were 0.29 eV for CsPbCl₃, 0.25 eV for CsPbBr₃ and 0.39 eV for KMnCl₃. The vacancy diffusion coefficients of these materials were found to be verylarge. However, the impurity doping did not increase the ionic conductivity markedly because of small dopant solubility.     

Luminescence of different modifications of crystalline silicon dioxide: Stishovite and coesite

Luminescence of very small samples of single crystals of coesite and stishovite has been studied. The spectra were detected under ionizing radiation (X-ray and electron beam) and the decay kinetics of cathodoluminescence in the range of time from 10 ns to 3 ms was measured. The coesite luminescence possesses a broad band at 3 eV with exponential decay about 680 μs at 80 K. The nature of this luminescence was explained as a self-trapped exciton creation in tetrahedron framework. The stishovite luminescence possesses two bands—blue (2.8 eV) and UV (4.7 eV). The UV band intensity grows more than 20 times with irradiation dose from initial level. This shows that the corresponding luminescence centers could be induced by the radiation. The decay of the UV band possesses a fast and a slow component. The determination of the fast decay parameters is beyond the capabilities of our apparatus (less than 10 ns), whereas the slow decay of the UV is non-exponential and takes place in the range of hundreds of microsecond. The blue band decay kinetics can be well approximated by power law ∼t⁻², which may correspond to recombination of defects created by radiation. The stishovite single crystal luminescence is very similar to that of germanium dioxide single crystal of rutile structure. The nature of the stishovite luminescence is explained as recombination of defects created by irradiation in octahedron-structured lattice.     

Anomalous luminescence of impurity-bound excitons in lithium borate crystals doped with cerium ions

The spectra and relaxation kinetics of the anomalous (?? < 10 ns) luminescence of Li₆GdB₃O₉:Ce³⁺ crystals have been experimentally detected. The time-resolved vacuum ultraviolet spectroscopy study has shown that optical transitions at 6.2 eV, caused by the transfer of an electron from the 4f ¹ ground state of Ce³⁺ to autoionizing states near the conduction band bottom of a crystal, lead to the formation of an impurity-bound exciton with the hole component localized on the 4f state of Ce³⁺ and the electron localized on states of the conduction band bottom. It has been found that the decay of such an exciton in Li₆GdB₃O₉:Ce³⁺ occurs through radiative recombination, leading to fast luminescence at 4.25 eV. The energy threshold for the formation of the impurity-bound exciton has been determined. The distribution functions of elementary relaxations over the reaction rate constants H(k), which determine the relaxation kinetics and luminescence quenching processes, have been calculated.     

Ultraviolet luminescence of Li6Gd(BO3)3: Ce crystals under selective excitation in the region of 4d → 4f transitions

The subnanosecond time-resolved ultraviolet luminescence of Li₆Gd(BO₃)₃: Ce crystals under selective excitation by ultrasoft X-rays in the region of the 4d??4f core transitions at temperatures of 7 and 293 K has been investigated for the first time. The performed investigation has revealed the following features: an intense fast component of the luminescence decay kinetics in the subnanosecond range due to the high local density of electronic excitations and the processes of Auger relaxation of the core hole; the modulation of the luminescence excitation spectrum by the ??giant resonance?? absorption band of the 4d-4f photoionization in the energy range 135?C160 eV; and a new broad luminescence band at an energy of 4.44 eV due to the direct radiative recombination between the genetically related electron in the states of the conduction band bottom and hole in the 4f ground state of the Ce³⁺ ion.     

Relaxation dynamics of Mn2+ intraion excitation in Cd0.5Mn0.5Te: Dependence on the optical pumping level

A study is reported of the Mn²⁺ intracenter 3d luminescence in a dilute Cd_0.5Mn_0.5Te magnetic semiconductor at pulsed excitations of up to 3.5 MW/cm². At high excitation levels and at a temperature of 77 K, the kinetics varies strongly over the emission band profile. The luminescence decay curve can be resolved into a fast and a delayed component, which correspond to the excitation of extended and localized states in the manganese ion system. The fast relaxation of the extended states is largely determined by the up-conversion. As the temperature is lowered, the contribution of the fast component at the center of the emission band and in its low-energy wing decreases because of the weakening role of the extended states lying above the mobility edge.     

Luminescence self-quenching in Tm3+: YLF crystals: II. The luminescence decay and macrorates of energy transfer

Microparameters of migration and self-quenching of luminescence from the (³ P ₀, ¹ I ₆) levels of Tm ³⁺ ions are calculated and the luminescence decay from the ³ H ₄, ¹ G ₄, and ¹ _{D 2} levels are analyzed in the concentration series of LiY_1?x Tm_xF₄(x=0.5–10 at. %) crystals upon weak selective excitation. It is shown that the luminescence decay of a thulium ion concentration higher than 0.5 at. % cannot be described by the energy transfer that takes into account only the dipole-dipole interaction. The comparison of experimental kinetic curves with theoretical curves calculated within the framework of the known energy transfer models showed that multipole-multipole interaction is responsible for the self-quenching of the thulium levels. Contributions of higher multipole interactions to the self-quenching are estimated. The decay of luminescence from the ³ H ₄, ¹ G ₄, and ¹ D ₂ levels of Tm³⁺:YLF crystals with different concentrations of thulium ions is described analytically.     

Interaction of dyes with nanoclusters adsorbed on the surface of AgBr microcrystals

We have performed a comparative luminescence investigation into spectral sensitization with dyes of holographic emulsions that contain AgBr microcrystals and are subjected to chemical sulfur or reducing sensitization. We show that, upon spectral sensitization of silver sulfide (Ag₂S) _n nanoclusters located on AgBr microcrystals, the polylayer adsorption of dyes on the surface of nanoclusters is observed, which is caused by van der Waals forces in the J-aggregated state. For silver oxide (Ag₂O) _m nanoclusters located on AgBr micro-crystals, the adsorption of dyes on their surface occurs only if chlorine atoms of heterocyclic residues of the dye interact with the nanocluster surface, which determines the adsorption of the dye as its chemisorption. In the remaining investigated cases, the polylayer adsorption of dyes during the spectral sensitization occurs not on the surface of nanoclusters but rather on the surface of AgBr microcrystals, initially in the J-aggregated state and then in the molecular- and H-aggregated states.     

Luminescence kinetics of an Y0.8Yb0.2F3:Tm3+ solid solution crystal

Upconversion luminescence kinetics of Tm³⁺ doped Y_0.8Yb_0.2F₃ solid solution crystal was studied for various values of pulse excitation parameters: pulse duration, wavelength and excitation power. Analysis of obtained results allowed a conclusion about the presence of transient processes. The transient processes found in upconversion luminescence kinetics are characterized by duration commensurate with lifetime of the excited energy levels of the activator ions. Upon completion of these processes a stable equilibrium state is established between the processes of population and spontaneous decay of the excited energy levels of Tm³⁺ ions. Conditions under which the equilibrium state can be maintained have been considered.     

The special features of the luminescence and light resistance of europium complexes and their mixtures with lanthanum complexes in polymethyl methacrylate

The kinetics of luminescence and transformation of short-lived products of the photolysis of europium and lanthanum complexes with thenoyltrifluoroacetone and 1,10-phenanthroline and their mixtures in polymethyl methacrylate films was studied by the nanosecond laser photolysis method with recording both light emission and absorption. Fast (535 and 585 nm, ⁵ D ₁ → ⁷ F ₀, ⁷ F ₃, decay time 0.7 μs) and slow (613 nm, ⁵ D ₀ → ⁷ F ₂, luminescence rise and decay times 0.7 μs and 0.5 ms, respectively) luminescence was studied. Induced absorption with a maximum at 600 nm and decay time ∼3 ms was observed; this absorption was assigned to triplet states of the deprotonated form of thenoyltrifluoroacetone. The dependences of luminescence intensity on the concentration of the components in a mixture of complexes were analyzed, and synergistic effects of luminescence strengthening were estimated. The kinetics of a decrease in luminescence intensity during photolysis was studied. Possible mechanisms of a decrease in the relative initial process rate and an increase in the quasi-stationary value of relative luminescence intensity as the concentration of complexes in the polymer increased were discussed.     

Photoluminescence and photocatalytic activity of zinc tungstate powders

ZnWO₄ powders with grain size in range 20 nm–10 μm have been synthesized by a simple combustion method and subsequent calcinations. The photocatalytic activities of powders were tested by degradation of methylene blue solution under UV light. The luminescence spectra and luminescence decay kinetics were studied and luminescence decay time dependence on average powder-grain size was obtained. The correlation between self-trapped exciton luminescence decay time and photocatalytic activity of ZnWO₄ powders was shown. A model explaining the excitonic luminescence decay time correlation with photocatalytic activity was proposed.     

Intrinsic luminescence of rare-earth oxyorthosilicates

The spectra and decay kinetics of luminescence and the excitation and reflection spectra of the luminescence of orthosilicates A ₂SiO₅ (A = Y, Lu, Sc, Gd), both nominally pure and doped with cerium, are measured using time-resolved VUV spectroscopy in the ranges of energies ?ν = 1.5–16 eV and temperatures T = 8–3000 K. The band structure of the crystals is calculated in the local electron density approximation (LDA). The origin of the intrinsic luminescence in the crystals studied is established, and the assumption regarding the existence of self-trapped excitons and their structure is made.     

The luminescence of ZnO ceramics

The luminescence properties of ZnO ceramics with grains 100–5000 nm sintered by different techniques from nanopowders were studied. The luminescence decay times were compared with that obtained for ZnO single crystal. The temperature dependence of non-exponential decay of defect luminescence (2.0–2.6 eV) was measured in wide time, intensity and temperature range. The luminescence decay kinetic at T ≤ 20 K shows the decay close to I(t) ～ t^?1 dependence. At temperature region 50–250 K the decay kinetics is more complicate since the TSL was observed in this temperature region. It is shown that the luminescence properties of NP and ceramics strongly depend on defect distribution on grains surface and the volume/surface ratio determine the luminescence decay in ZnO nanostructures and ceramics.     

PbWO<Subscript>4</Subscript> crystal for laser energy accumulation and transformation

The picosecond interband two-photon laser excitation of PbWO₄ crystals at a temperature of 10 K leads to electronic excitation energy accumulation, which results in almost 100% induced absorption in the 450–750 nm spectral range. The relaxation time of this induced absorption exceeds 100 min. The electronic excitation energy accumulated in the PbWO₄ crystal at T = 10 K excites the intrinsic luminescence with a decay time longer than 45 min. The decay kinetics and the spectra of the intrinsic luminescence of the PbWO₄ crystal at a temperature of 10 K were measured under two-photon and single-photon excitation. The luminescence under two-photon and single-photon excitation revealed a difference in the structure of the spectra.