Formation of La-containing microcrystals in KCl and NaCl matrices

The mechanism of the K₂LaCl₅ and LaCl₃ aggregate formation in KCl and NaCl matrices as a result of long-term annealing is discussed. Thermodynamic analysis of formation conditions of such aggregates has been performed. The influence of diffusion processes and the elastic deformation of aggregates by the matrix are considered. It has been shown that Ce and Pr as activator ions penetrate efficiently into aggregates.Обговорюється механізм утворення агрегатів K₂LaCl₅ та LaCl₃ у матрицях КСl та NaCl, відповідно, внаслідок тривалого відпалу. Проведено термодинамічний аналіз умов формування таких лантановмісних мікрокристалів. Враховується вплив дифузійних процесів та енергії пружної деформації мікрокристалів зі сторони матриці та умови фазоутворення у композитах, що досліджуються. Показано, що іони Се та Pr у ролі активаторів за малих концентрацій і тривалого відпалу ефективно входять в агрегати K₂LaCl₅ та LaCl₃.Обсуждается механизм образования агрегатов K₂LaCl₅ и LaCl₃ в матрицах, соответственно, KCl и NaCl в результате продолжительного отжига. Проведен термодинамический анализ условий формирования таких лантансодержащих микрокристаллов. 'Учитывается влияние диффузионных процессов и энергии упругой деформации микрокристаллов под действием матрицы на условия фазообразования в исследуемых композитах. Показано, что ионы Се и Pr эффективно входят в агрегаты K₂LaCl₅ и LaCl₃ в качестве активаторов

Quenching of exciton luminescence in SrF2\mathrm{SrF_2} nanoparticles within a diffusion model

Quenching processes of the self-trapped exciton luminescence were studied analyzing the shape of X-ray luminescence decay kinetics curves of SrF$_2$ nanoparticles of different sizes. To describe the curves of luminescence decay kinetics, an equation was obtained which is based on the model which takes into account the diffusion of self-trapped excitons and which considers the case of strong surface quenching. The obtained relation was shown to describe the shape of the experimental curves of X-ray luminescence decay kinetics of SrF$_2$ nanoparticles if their size distribution is bi-modal, i.e., a log-normal distribution about a mean size in the tens of nanometers range plus a distribution of particles larger than 130 nm. The presence of large particles is implied in this model by the single-exponential decay with time constant of 1.2 μs. From the fitting of kinetics curves using the proposed relation, the average diffusion length of self-trapped excitons in SrF$_2$ was estimated to be (15 ± 2) nm

Luminescence of the SrCl2:PrSrCl_{2}:Pr crystals under high-energy excitation

The present research was carried out in order to elucidate the mechanisms of energy transfer from the crystal lattice to Pr3+ ions in SrCl2. The luminescence excitation and emission spectra as well as luminescence kinetics of the SrCl2:Pr single crystals containing 0.2 mol% Pr were investigated at 300 and 10 K using the vacuum ultraviolet (VUV) synchrotron radiation. The X-ray excited luminescence spectra of the SrCl2:Pr (CPr=0.2 and 0.5 mol%) and SrCl2:Pr, K (CPr=1.5 mol%; CK=1.5 mol%) crystals were studied at 294 and 80 K. Under optical excitation of the samples in the Pr3+ absorption bands, there were observed five fast ultraviolet emissions assigned to the 4f15d→4f2 transitions, and two long-wave bands corresponding to the f–f transitions. Furthermore, the intrinsic emission bands of SrCl2 were observed at 10 K. The X-ray excited luminescence spectrum of the SrCl2:Pr crystal containing 0.2 mol% Pr, besides intrinsic emission band near 400 nm, has got a long-wave band at about 490 nm of the Pr3+ centers. There were not observed any emission bands of the Pr3+ centers corresponding to the 4f15d–4f2 transitions in the X-ray excited luminescence spectrum of the SrCl2:Pr crystal. The possible mechanisms of energy transfer from the SrCl2 matrix to the Pr3+ centers are discussed