Spectral and structural characteristics of Lu_{1 – x – y} Ce _x Tb _y BO₃ orthoborates prepared by the hydrothermal synthesis method

Abstract

The structure, IR absorption spectra, morphology, and photoluminescence spectral characteristics of Lu_1–x–y Ce _x Tb _y BO₃ solid solutions prepared by the hydrothermal synthesis method have been investigated. According to the X-ray powder diffraction data, the Lu_1–x–y Ce _x Tb _y BO₃ samples hydrothermally synthesized at a temperature T = 200°C have the vaterite structure, and all the observed diffraction peaks correspond to the hexagonal phase with the space group P6₃/mmc, which is isostructural to pure lutetium borate LuBO₃. Annealing of these samples at T = 970°C leads to a change in the structural modification and to the transition of the samples to the monoclinic phase with the space group C2/c. It has been found that, after annealing of these samples at temperatures T = 800–970°C, the luminescence intensity of Tb³⁺ ions upon excitation in the absorption band of Ce³⁺ ions increases by more than two orders of magnitude and becomes much higher than that in compounds of the same composition, but prepared by high-temperature synthesis. At the same time, annealing of lutetium borate doped only with terbium does not lead to a significant change in the luminescence intensity of Tb³⁺ ions. The possible reasons for a multiple increase in the luminescence intensity of terbium ions due to the annealing of the hydrothermally synthesized lutetium orthoborate samples doped with cerium and terbium ions have been discussed.