In order to identify the mechanisms of the scintillation process under the size confinement, the study of luminescence parameters under the optical and X-ray excitation of SrF2:Ce nanoparticles obtained by the chemical precipitation method has been performed. The main features of the X-ray-excited and photoluminescence spectra of SrF2-Ce nanoparticles of 82 nm and 65 nm sizes well match with the luminescence parameters of bulk materials and reveal the characteristic doublet emission band of Ce3+ ions with maximums at 310 and 329 nm, which correspond to the electronic transitions from 5d-levels to the 4f ground state of cerium ion (F-2(5/2) and F-2(7/2)) split by spin-orbital interaction. In the luminescence excitation spectra in the matrix transparency range between 3.9 and 7.1 eV, the excitation bands corresponding to intracenter 4f-5d-absorption transitions of cerium ions are observed. The observed drop at 10.7 eV in the range of exciton reflection maximum is associated with the near-surface radiation-free loss of excitation energy. The structure of luminescence excitation spectra in the band-to-band region (12-20 eV) corresponds to the combined density of states of valence band and conduction band. The excitation threshold at 21.9 eV is related to the multiplication of electronic excitations in particular with the creation of secondary electrons. The intensity and time parameters of the luminescence, the features of the luminescence excitation spectra essentially depend on the nanoparticle sizes. The decrease of the luminescence intensity of cerium ions in the case of intracenter excitation is due to the resonant transfer of excitation energy to surface defects. The decrease of the luminescence decay time constant becomes significant for nanoparticles of sizes smaller than 20 nm, which indicates the dominant role of surface defects in this process. In the case of recombination luminescence (h(v) > E-g), an additional quenching channel appears caused by the escape of electrons from the nanoparticle volume when the thermalization length exceeds the nanoparticle size.

The experimental dependence of the luminescence intensity of YVO4:Eu nanoparticles on their size in the range from 8 to 16 nm is studied. It has been shown that the decrease of the X-ray excited luminescence intensity with the decreasing size of the nanoparticle is caused both by quenching resulting from the interaction of luminescent centres with surface defects and by losses of excitation energy at the stage of thermalisation. A method of calculating the dependence of the X-ray excited luminescence intensity on the nanoparticle size is proposed based on the assumption that only the charge carries not reaching the near-surface layer of particle after the thermalization process give contribution to the recombination luminescence. The length of thermalisation was calculated taking into account the dependence of the effective mass of electrons on their kinetic energy. The average value of the effective mass of electrons in the conduction band with the kinetic energy in the range [0, E-g] is estimated to be 1,5me. The distribution of secondary electrons by the thermalisation lengths for YVO4 is obtained and its average value is estimated to be 6 nm. The minimum size of YVO4 nanoparticles possessing the intensity of X-ray excited luminescence approximately twice smaller comparing to the bulk crystal is theoretically estimated to be 27 nm. This value is significantly smaller than any visible light wavelengths that minimize all processes of light scattering and it gives an opportunity to create composite polymer-inorganic materials based on these nanoparticles for X-ray registration.

8nm and 16 nm YVO4:Eu nanoparticles have been synthesized by the low temperature chemical method and annealed at T - 800 degrees C. The nanocomposite films based on scintillation polystyrene loaded with YVO4:Eu (40 wt%) nanoparticles have been obtained. The luminescence- kinetic characteristics of YVO4:Eu nanoparticles and nanocomposites have been investigated. The luminescence of the polystyrene nanocomposite loaded with YVO4:Eu (40 wt%) nanoparticles reveals the bands characteristic of the luminescent impurities of p- Terpinil (370 nm), POPOP (420 nm) and of YVO4:Eu nanoparticles (D-5(0) -> F-7(1) band) at 590 nm, the band D-5(0) -> F-7(2) at 617 nm, and the weaker D-5(0) -> F-7(3) (590 nm) and D-5(0) -> F-7(4) (700 nm) bands. The intensity of X-ray excited luminescence of the polystyrene composites loaded with YVO4:Eu nanoparticles (40 wt%) increases 3 times. The luminescence decay kinetic of the polystyrene composite in the case of X-ray excitation reproduces the decay kinetic curve of pure polystyrene scintillator with the time constant of similar to 2.7 ns. The contribution of Eu3+ luminescence to the scintillation pulse is insignificant due to the significant decrease of the luminescence intensity of Eu3+ centers with decreasing nanoparticle sizes, and the decay time constant of Eu3+ luminescence (tau = 0.8 ms) is significantly greater than the duration of the main scintillation pulse. The increase in the detection efficiency of the ionizing radiation by the nanocomposite is caused by the increase in the absorption capacity. The increase in absorption is caused by the presence of heavy inorganic YVO4:Eu nanoparticles compared to the polystyrene matrix without any nanoparticles and by the transfer of excitation energy from embedded nanoparticles to the polystyrene matrix due to the electron escape from YVO4:Eu nanoparticles into the host matrix. The discrepancy between the calculated and observed efficiency detection for the nanocomposite is due to the aggregation of nanoparticles, which prevents the escape of electrons from nanoparticles into the polystyrene matrix.

Intrinsic luminescence of the undoped (LaLu)(3)Lu2Ga3O12 garnet (LLGG) single crystals with high concentration of Lu-La antisite defects (AD) has been studied for the first time under excitation by 1.5 ns pulse X-ray radiation. It has been found that the host luminescence of LLGG crystal consists of two emission bands in the UV range. The band peaked at 3.80 eV at 77 K has been related to the luminescence of localized excitons (LE) perturbed by the presence of AD whereas the band peaked at 3.37 eV has been related to the radiative annihilation of bound-state excitons localized directly at Lu-La AD. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The absorption and cathodoluminescence spectra of single crystalline films (SCF) of Y3Al5O12:Bi garnet depending on Bi concentration were analyzed. For consideration of the nature of the UV and visible Bi-related emission bands the time-resolved luminescence of Bi3+ (ns2) ions in YAG:Bi SCF was studied at 10 K under excitation by synchrotron radiation. The difference in the excitation spectra and emission decay of the UV and visible bands has been explained via radiative relaxation from the P1,03 excited states to the S01 ground state of the isolated and pair/clustered Bi3+ emission centers in the garnet lattice, respectively.

Existence of effective energy transfer from matrix (Tb3+ cations) to Ce3+ ions has been shown in TbAG:Ce single crystalline films (SCF) by means of investigation of the time-resolved emission and excitation spectra as well as luminescence decay under excitation by synchrotron radiation.

The studies of luminescence and the luminescence excitation spectra of the pure and Ce3+-doped Cs3LaI6 single crystals at 9 and 77 K are reported. The doublet band of STE emission (maxima at 2.57 and 2.81 eV) was revealed in the luminescence spectrum of pure Cs3LaI6 crystal at 9 K. The band gap value (4.3 eV) has been estimated for the Cs3LaI6 crystal taking into account the presence of characteristic dip in the excitation spectrum of STE emission at 3.85 eV caused by the excitonic reflection. The doping of the Cs3LaI6 crystal by Ce3+-ions results in the appearance of the cerium doublet (peaking at 2.57 and 2.81 eV) as well as the near-impurity localized exciton band (3.60 eV) in the luminescence spectra at 9 K. The slow decay component (tau > 150 ns) dominates in the cerium emission under the excitation in the fundamental absorption range that confirms the excitation energy transfer from the crystalline matrix to the impurity centres.

The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu3Al5O12 (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of LuAl antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and LuAl antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb2+ ions. The structure of the luminescence centers, related to the background emission of impurity Pb2+ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides (Al2O3, Y2O3) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O− ions and electrons localized at excited levels of Lu3+ cations.