S. Zazubovich

Photoluminescence of Cs4PbBr6 crystals and thin films

Abstract Absorption, emission and decay kinetics characteristics of Cs 4 PbBr 6 bulk and thin film samples were measured in the UV–visible spectral range over 4.2–250 K. An emission band at 375 nm was ascribed to the Cs 4 PbBr 6 structure itself with two excitation maxima round 310 and 240 nm coinciding with absorption peaks in the thin film absorption spectrum. The coexistence of Cs 4 PbBr 6 and CsPbBr 3 phases was evidenced in both the bulk and thin film systems.

Physics of halide scintillators

Abstract The paper reviews the results obtained within the last 5–6 years in the field of the physics of some halide crystals which have led to a better understanding of their characteristics. The luminescence and scintillation characteristics of caesium iodides, widely used in the existing detectors, as well as the properties of some other selected materials are discussed in view of their possible applications. For all the systems concerned, the emission important for their practical applications arises from the radiative decay of excitons of various types. The following features are considered in more detail: (1) the excited states structure, the mechanism of excitation of the localized exciton emission in the impurity-induced absorption bands, the processes of defects creation, and the scintillation mechanism in CsI : Tl and CsI : Na scintillators; (2) the luminescence of on-centre excitons in CsI and RbI crystals; (3) the luminescence of free cation excitons in the CsPbX3-type aggregates thermally created in CsX : Pb single crystals (X=Cl, Br); (4) the model of the excited states responsible for the cation exciton luminescence of lead halides.

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 of CsPbCl3 Nanocrystals Dispersed in a CsCl Crystal under High-Energy Excitation

The luminescence spectral and kinetic characteristics of CsPbCl3 nanocrystals, thermally created in a CsCl:Pb single crystal and dispersed in a CsCl matrix, have been studied under excitation by synchrotron radiation in the VUV spectral region (4 to 20 eV). Various components found in the decay kinetics of the 2.98 eV emission have been connected with the direct excitation of the CsPbCl3 luminescence and with the reabsorption of luminescence of other emitting centers by the CsPbCl3 nanocrystals. A high-energy shift of the free exciton emission band maximum of the CsPbCl3 nanocrystals with respect to that observed for a CsPbCl3 single crystal as well as the shortening of the luminescence decay time are considered from the point of view of quantum size effects.

Polarized luminescence of CsPbBr3 nanocrystals (quantum dots) in CsBr:Pb single crystal

Abstract Polarization of the free exciton luminescence of CsPbBr 3 -type semiconducting nanocrystals of perovskite structure dispersed in CsBr:Pb crystal has been observed for the first time. The polarization spectra, temperature and angular dependences of the degree of polarization as well as the dependence of polarization characteristics on size and shape of CsPbBr 3 nanocrystals have been studied. The conclusions have been made about the orientation of anisotropic CsPbBr 3 nanocrystals with respect to CsBr crystal axes, the origin of optical transitions responsible for the exciton emission as well as about the mechanism of the production of the nanocrystals in the process of thermally stimulated diffusion of Pb 2+ ions in CsBr:Pb crystal lattice.

Relaxed excited state structure and luminescence of thallium-doped caesium chloride and bromide

Four bands, all belonging to the main thallium centres, have been detected in the emission spectra of CsCl:Tl and CsBr:Tl crystals. Their spectral, polarization and kinetic characteristics have been studied from 0.45 up to 360 K. It has been shown that the new model proposed by us recently for the relaxed excited state (RES) structure of the luminescence centre in CsI:Tl crystals is valid for CsCl:Tl and CsBr:Tl crystals as well. Two ultraviolet emission bands excited mainly in the A absorption band of Tl+ centres are ascribed to electronic transitions from trigonal and tetragonal Jahn-Teller minima of the tripler RES of Tl+. Two visible bands excitable mainly in the higher energy absorption bands of CsCl:Tl and CsBr:Tl are connected with two different off-centre configurations of self-trapped exciton perturbed by the Tl+ ion. The parameters of the corresponding excited state minima have been calculated. The mixing of the impurity and halogen excited states has been shown to decrease markedly in the sequence of anions I- --> Br- --> Cl-.

Quantum size effect in the excitonic luminescence of CsPbX3-like quantum dots in CsX (X = Cl, Br) single crystal host

Copyright (c) 1997 Elsevier Science B.V. All rights reserved.Luminescence of CsPbX 3 -like quantum dots in CsX crystal host (X=Cl, Br) is reported. Single band spectrum is found for as grown or heavily annealed (T=240°C) CsX:Pb, while a family of emisssion bands is observed after annealing at temperatures below 210°C. Anisotropic growth of quantum dots in the early stage is proposed and positions of emission peaks are calculated for CsPbCl 3 quantum dots using a simple model.

On the origin of cerium-related centres in lead-containing single crystalline films of Y2SiO5?:?Ce and Lu2SiO5?:?Ce

Absorption, electron spin resonance, and photo- and thermally stimulated luminescence characteristics are studied for single crystalline films (SCFs) of Y2SiO5?:?Ce and Lu2SiO5?:?Ce prepared by the liquid phase epitaxy method with the use of a PbO-containing flux. They are also compared with the characteristics of the corresponding single crystals (SCs) as well as of the undoped Y2SiO5 and Lu2SiO5 SCFs and SCs. The concentration of stable trivalent Ce3+ ions in various SCFs with different lead and cerium contents is found to be negligible. It is suggested that stable tetravalent Ce4+ ions mainly exist in the SCF due to a large concentration of Pb2+ ions whose excess volume and negative charge can be effectively compensated by relatively small tetravalent Ce4+ ions. Nevertheless, the characteristic Ce3+ emission in the SCFs of Y2SiO5?:?Ce and Lu2SiO5?:?Ce does appear under photoexcitation in the charge-transfer absorption region (Eexc?>?4.2?eV), most probably as a result of the two-photon excitation process. Ce3+ emission is observed under excitation by the ionizing radiation as well and is explained by the recombination of free electrons from the conduction band with Ce4+ ions.

Physics of Lead Tungstate Scintillators

A brief review of recent results, obtained during a systematic study of the luminescence and photo-thermally stimulated defects creation processes in various undoped and doped lead tungstate crystals, is presented. The origins of various emission bands are clarified. Several types of localized excitons are identified and their decay into electron and hole centers is found. The origin of the centers, created at the decay of the self-trapped and localized exciton states and the defect-related states, is studied both by the thermally stimulated luminescence (TSL) and the electron spin resonance (ESR) methods. The origin of the TSL peaks and the mechanisms of the defect creation and recombination processes are discussed.

Coexistence of the impurity and perturbed exciton levels in the relaxed excited state of CsCl:Pb crystal

Four bands, all attributable to the main lead centres, have been detected in the emission spectrum of CsCl:Pb crystals. Their spectral and kinetic characteristics have been studied from 1.8 K up to 300 K, and the parameters of the corresponding relaxed excited states (RES) are calculated. It has been shown that the new model proposed by us recently for the RES structure of the luminescence centre in CsI:Tl is valid for CsCl:Pb as well. Two ultraviolet emission bands (at 4.0-3.9 eV and 3.55 eV) excited mainly in the A absorption band of centres (4.65 eV) are ascribed to electronic transitions from Jahn-Teller minima of two types of the triplet RES of the ion. The higher-energy band is split into two components due to the presence of a cation vacancy near . Two visible bands (at 2.6 eV and 1.97 eV) are connected to two different off-centre configurations of excitons localized near the ion.