A. Krasnikov

Pr3+-doped complex oxide single crystal scintillators

We investigate and compare optical absorption, luminescence and scintillation properties of Pr-doped Y3Al5O12, Lu3Al5O12, Y2SiO5 and Lu2SiO5 single crystals. The processes determining the kinetics of the fast Pr3+ 5d–4f radiative transition are described. Among the studied host materials, only Lu3Al5O12 presents neither any 5d1–4f luminescence state nonradiative quenching nor Pr3+ ionization at room temperature. We evaluate the figure of merit of all materials for application as scintillators. The most promising system appears to be Lu3Al5O12 : Pr, since it combines an elevated density of 6.67 g cm−3, a fast scintillation response dominated by a 21 ns decay time and a spectrally corrected light yield about 160% with respect to that of Bi4Ge3O12 (BGO).

A role of Gd3+ in scintillating processes in Tb-doped Na–Gd phosphate glasses

Abstract Sensitization role of Gd 3+ ions in energy transfer processes in radio- and photo-luminescence is described for Tb 3+ -doped and Gd-enriched Na x Gd y phosphate glasses. Limited (Gd–Gd) n energy migration is obtained and the Gd 3+ →Tb 3+ transfer is explained as due to mainly the (super) exchange interaction. These results are discussed and compared with the situation observed in similar glasses or crystals where transfer processes are mainly due to multi-polar interaction (Gd 3+ →Ce 3+ or Ce 3+ →Gd 3+ ) and more efficient migration among Gd 3+ ions that is observed.

Luminescence characteristics and energy transfer in the mixed YxGd1?xF3:Ce, Me (Me = Mg, Ca, Sr, Ba) crystals

The luminescence spectra and decay kinetics are measured within 80–300 K for the set of mixed YF3–GdF3 single-crystal fluoride hosts doped by the Ce3+ and Me2+ (Me = Mg, Ca, Sr, Ba) ions. For certain Ce and Me concentration ranges we observe creation of the Ce3+-distorted luminescence centre with the emission maximum around 380–390 nm. Energy migration through the Gd sublattice and a transfer to the Ce3+-distorted centre is evidenced and modelled using a simple Stern–Volmer approximation.

On the Interpretation of Luminescence of Lead Halide Crystals

Emission and excitation spectra, and the luminescence decay kinetics have been studied for PbCl 2 crystals at the temperatures 0.45-100 K. It has been found that even at the lowest temperatures, where the non-radiative decay of exciton states in PbCl 2 does not take place, the decay times of both the ultraviolet (UV) and the blue (B) exciton emission are by a few orders of magnitude shorter than the decay times of the emission arising from the triplet relaxed excited state of Pb 2- centres in lead-doped ionic crystals. A conclusion has been drawn that the luminescence of lead halides cannot be connected with single Pb 2+ ions. It is proposed that the radiative decay of the self-trapped excitons of the type of [(Pb 2 ) 3+ + hole} is responsible for the UV and the B emission of PbCl 2 crystals, while the lowest-energy (BG) emission arises from the tunnelling recombinations between the (Pb 2 ) 3+ -type self-trapped electrons and V K -type self-trapped holes.

Luminescence of lead-related centres in single crystalline films of Lu2SiO5

The steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics of nominally undoped Lu2SiO5 single crystalline films (SCFs) grown by the liquid phase epitaxy method from the PbO-based flux are studied in the range 4.2–300 K. Due to the preparation method, the films contain lead ions. Luminescence characteristics of Pb-related centres of different types are identified. A weak 3.65 eV emission is ascribed to the radiative decay of the triplet relaxed excited state (RES) of Pb2+ ions substituting for Lu3+ ions in the Lu1 lattice sites of the X2 structure. Possible origins of the intense complex lead-related ≈2.8 eV emission are discussed. We propose phenomenological models describing the excited-state dynamics of the studied luminescence centres. We also determine the characteristic parameters of the corresponding RESs, in particular, the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states.

Localized excitons and their decay into electron and hole centres in PbWO4 single crystals grown by the bridgman method

Lead tungstate crystals grown by the Bridgman method are oxygen deficient. Therefore they are suitable objects for the detailed study of various oxygen vacancy-related defects. The processes of luminescence and photo-thermally stimulated defect creation were studied at 80–350 K under selective UV irradiation in the 5.0–3.5 eV energy range for as-grown and 600 °C air annealed PbWO4 crystals (grown in both cases by the Bridgman method). The creation of defects reveals itself in the appearance of thermally stimulated luminescence (TSL) peaks and electron spin resonance signals. Dependences of the TSL peak intensity on the irradiation energy, temperature and duration were investigated. In the crystals studied the observed characteristics are explained by the presence of excitons localized at oxygen-deficient anion complexes of different types (WO3, WO2, WO) and the photo-thermally stimulated decay of these excitons into electron and hole centres. The origin of these centres and their creation processes are discussed.

Luminescence and creation of electron centers in UV-irradiated YAlO3 single crystals

Luminescence and defect creation processes were studied by the photoluminescence, thermally stimulated luminescence, and electron paramagnetic resonance methods in the UV-irradiated single crystals of undoped YAlO3, containing small amounts of Ce, Mo, and Ti ions as accidental impurities. The luminescence of the electron antisite YAl2+-type centers of different structures was found around 2.45 eV and studied at 4.2–500 K. The luminescence of the Ti3+-related centers (2.03 and 1.73 eV) and Ti4+ centers (2.78 eV) was observed as well. Dependences of the number of the YAl2+-type and Ti3+-related centers on the UV irradiation energy, temperature, and duration, as well as on various crystal heat-treatment procedures were examined. As a result of the photostimulated electron transfer from the O2− ligand ions to Mo4+ and Ti4+ ions, the paramagnetic hole O−-type centers and electron Ti3+ and Mo3+ centers are created. The antisite YAl2+-type centers are created due to the photostimulated release of electrons mainly from the Mo3+ centers to the conduction band and their subsequent trapping at the YAl3+ ions located near an oxygen vacancy or a defect at the neighboring Y3+ site.Luminescence and defect creation processes were studied by the photoluminescence, thermally stimulated luminescence, and electron paramagnetic resonance methods in the UV-irradiated single crystals of undoped YAlO3, containing small amounts of Ce, Mo, and Ti ions as accidental impurities. The luminescence of the electron antisite YAl2+-type centers of different structures was found around 2.45 eV and studied at 4.2–500 K. The luminescence of the Ti3+-related centers (2.03 and 1.73 eV) and Ti4+ centers (2.78 eV) was observed as well. Dependences of the number of the YAl2+-type and Ti3+-related centers on the UV irradiation energy, temperature, and duration, as well as on various crystal heat-treatment procedures were examined. As a result of the photostimulated electron transfer from the O2− ligand ions to Mo4+ and Ti4+ ions, the paramagnetic hole O−-type centers and electron Ti3+ and Mo3+ centers are created. The antisite YAl2+-type centers are created due to the photostimulated release of electrons mainl...

Defect Creation under UV Irradiation of CsI:Pb Crystals in Pb2+-Induced Absorption Bands Investigated by Luminescence Methods

The creation of defects in CsI:Pb crystals by ultraviolet radiation at 4.2 K has been investigated by thermally stimulated and optically stimulated luminescence methods. The origin of the optically created defects has been established. The dependences of the defect creation efficiency on the irradiation energy and time, on the uniaxial stress, and on the concentration of the impurity (Pb 2+ and Na + ) ions have been found. The charge-transfer processes taking place under irradiation of CsI:Pb crystals in the Pb 2+ -related absorption bands and resulting in the appearance of the self-trapped and localized exciton luminescence and in defect creation have been explained.

Ultraviolet luminescence and creation of (WO4)3−-type centers under UV irradiation of PbWO4 crystals doped with trivalent rare-earth ions

Luminescence characteristics and creation of (WO4)3− and (WO4)3−-A3+ centers were studied in PbWO4 crystals doped with trivalent rare-earth A3+ ions (A3+: La3+, Lu3+, Y3+, Ce3+, Gd3+, Eu3+) under selective irradiation in the 3.4-5.0 eV energy range at 5–80 K. Optically created centers were detected by the TSL and ESR methods. Creation spectra of the mentioned centers were measured and the activation energies needed for their creation were calculated. It was found that both the (WO4)3−and (WO4)3−-A3+ centers can be created not only in the band-to-band transitions region but also in the 3.8 ± 0.4 eV range. The activation energy for their creation at T 60 K, the activation energy for (WO4)3−-A3+ centers creation varies from 10 to 25 meV, depending on the irradiation energy. A new UV emission, peaking in the 3.05–3.20 eV range, was found whose thermal quenching takes place with the same activation energy. Radiative decay of defect-related states, as well as the processes of their non-radiative decay, resulting in creation of (WO4)3−-A3+ centers and thermal quenching of the UV emission, are considered to explain the effects observed.

Time-resolved spectroscopy of Bi 3+ Centers in Y 4 Al 2 O 9 ceramics

Time-resolved emission and excitation spectra as well as luminescence decay kinetics are studied at 4.2-400 K under excitation in the 3-6 eV energy range for Bi³⁺ ions substituting for Y³⁺ ions in four nonequivalent crystal lattice sites of Y₄Al₂O₉:Bi ceramics. The dependences of the luminescence characteristics and the relaxed excited state structure of Bi³⁺centers on their nearest surroundings are discussed.