Pir P. Synthesis and luminescent properties of alkaline earth borates doped with lanthanide's ions

Оbject of investigation: alkaline earth borates. Aim of investigation: establishment of the influence of crystal and electronic structure on the luminescent properties of Ln2+(3+) ions in alkaline earth borates, identification of factors causing the stabilization of Ln2+ by a crystal structure and optimization of the conditions for preparation of effective luminescent and optical materials. Methods of investigation and instruments: X-ray analysis, differential thermal analysis, IR spectroscopy, luminescent spectroscopy. Results: Luminescent properties of Ln2+(3+) (Ln= Tm, Yb) ions in M2B5O9X (X= Cl, Br), MB6O10, MB2O4, (M= Ca, Sr) borates after high-temperature annealing in various atmospheres are reported and discussed. It was shown that the stability of Ln2+ increases in the sequence Sr3(BO3)2, Sr2B2O5<SrB2O4, SrB6O10, Sr2B5O9X < SrB4O7. This tendency can be explained by taking into account two factors, namely, condensation degree of borate anions and the differences in charge-compensating mechanismfor Ln3+. A simple criterion is proposed to predict stability of Ln2+ in alkaline earth borates. The influence of the crystal structure of alkaline earth borates on the spectral position of their fundamental absorption edge (?edge) is discussed. It was shown that the fundamental absorption edge tends to shift to higher energy from ?-BaB2O4 to SrB6O10, SrB4O7. The observed tendency can be considered as a result of a) a removal of s-alkaline earth states from the top of the valence band; b) a more efficient stabilization of the O 2p orbitals by covalent bonding with increasing condensation degree of the borate anions. Field of application: inorganic chemistry, electronic industry.