E. Mihóková

A study of electron excitations in and single crystals

The excitation spectra of photo- and thermo-luminescence were compared in the VUV - UV spectral region in and scheelite tungstates. Temperature dependences of emission intensities and decay times were measured for in the 80 - 300 K range and approximated by a simple phenomenological model. The energy level structure of the emission centre excited state and related kinetic processes are discussed for both tungstates.

Photoluminescence of Bi3+ in Y3Ga5O12 single-crystal host

Photoluminescence spectra and decay kinetics within 10–350 K were measured in the Bi-doped Y3Ga5O12 single crystal prepared by the micro-pulling-down technique. Temperature dependences of the decay times and the integrated emission intensities obtained from the experiment were simulated using a phenomenological two-excited-state-level model. The model provided quantitative parameters of the involved excited state levels of the Bi3+ luminescence centre in this host. The results are discussed in the light of already published data obtained for other Bi-doped compounds. The influence of the defects and structural irregularities of the host on the Bi3+ emission characteristics is discussed as well.

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.

Influence of Si-codoping on YAG:Ce scintillation characteristics

A set of undoped, Ce/sup 3+/-doped and Si/sup 4+/-codoped Y/sub 3/Al/sub 5/O/sub 12/ (YAG) single crystals were grown by the Czochralski method and submitted to /spl gamma/ irradiation in the dose range 1-236 Gy at RT. Their irradiation induced absorption coefficient was calculated and analyzed. Crystals also underwent light yield (LY) and scintillation decay measurements using the /sup 241/Am and /sup 22/Na radioactive sources, respectively, in 1 /spl mu/s time gate. The induced absorption at 550 nm (at the Ce/sup 3+/ luminescence peak) decreases with Ce concentration and further decrease is obtained in the Si/sup 4+/-codoped samples. LY values are independent on the Ce/sup 3+/ concentration within 0.12% - 0.3% and on the moderate Si/sup 4+/ codoping as well.

Slow relaxation, confinement, and solitons.

Millisecond crystal relaxation has been used to explain anomalous decay in doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons. Our model exhibits confinement of mechanical energy released by excitation. Extending the model to long times is justified by its relation to solitons, excitations previously proposed to occur in alkali halides. Soliton damping and observation are also discussed.

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.

The influence of defect states on scintillation characteristics of PbWO4

Abstract The effect of several stable trivalentions (Lu, Y and Gd) and pentavalent Nb5+ on the radiation resistance and thermoluminescence characteristics of PbWO4 is investigated. While rather uniform behaviour is observed for all the trivalent ions, apparently different mechanisms apply in the case of the Nb doping. This fact could be explained by different effect of the dopants on the oxygen sublattice, namely on the concentration of oxygen vacancies. Electron centers based on oxygen vacancy(ies) participate in thermoluminescence processes round 200 K.

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.

Spectroscopy and transfer processes in LuxGd1−xAlO3: Ce scintillators

Abstract Spectroscopic properties and energy transfer processes in Ce 3+ -doped RE 3+ AlO 3 orthoaluminates (for RE 3+ = Lu 3+ , Gd 3+ or Y 3+ ) or for the mixed Lu x Y 1− x and Lu x Gd 1− x are presented and summarised. Generally, spectroscopic properties of these crystals are very similar but in their Ce 3+ fluorescence and scintillation decay slow decay components appear. Temperature dependence of Ce 3+ fluorescence decays in Lu x Gd 1− x AlO 3 :Ce crystals show Ce 3+ → Gd 3+ nonradiative energy transfer followed by the opposite transfer Gd 3+ → Ce 3+ (including migration through Gd 3+ sublattice) which is responsible for slow Ce 3+ fluorescence decay component. Energy barrier between Ce 3+ and Gd 3+ interacting levels is ~ 70 meV.