Add time:08/11/2019         Source:sciencedirect.com

The monocrystals of ternary praseodymium bromides were obtained by Bridgman technique. The high resolution absorption emission and emission excitation spectra were studied in the UV, VIS and near-infrared regions at 293, 77 and 4 K. In these spectral regions the 4f–5d and f–f Pr(III) transitions were observed, and the splitting of the corresponding 2S+1LJ multiplets was compared to that of respective transitions in the K2PrCl5 monocrystal spectra. Changes of the spectral properties with concentration of active ions were observed mainly in the absorption spectra at low temperatures, clearly manifesting the ion–ion interaction in crystal lattice. The lowering of the emission in the concentrated system can be due to the concentration quenching and energy migration to the traps. On the other hand, somewhat different pathways of deexcitation of the excited states were detected in emission for ternary chlorides and bromides at the same concentrations. In halides (Cl, Br) the crystal field splitting and differences in emission properties can be also explained by subtle variations of electron–phonon coupling, decrease of phonon energies and increase of covalency. The f–d states provide a nonradiative channel of the excitation of the f–f states in the case of bromides. The feature of emission varies with energy of excitation where strong reabsorption was detected in stoichiometric crystals. The factors affecting excited state dynamics are analysed and discussed.

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