Photoluminescence from the 5D4 level of Tb3+ ions in K–Ba–Al fluorophosphate glass under pressure

Fluorescence spectra of Tb³⁺ ions in 55.5P₂O₅–17K₂O–14.5BaO–8Al₂O₃–4AlF₃–1.0Tb₄O₇ (PKBAFTb) glass have been measured as a function of high pressures up to 35 GPa at room temperature. A strong red shift of ⁵D₄ → ⁷F_J (J = 3, 4 and 5) transitions with different rates is observed under pressure, which is attributed to the increasing spin–orbit coupling constant, ζ_4f. There is a considerable pressure effect on the magnitude of the crystal-field splittings observed for the ⁵D₄ → ⁷F₄ and ⁷F₅ transitions. The increase in Stark splittings observed under pressure is due to pressure induced electrostatic interaction between the 4f electrons and their ligands. Decay times of the emission from the ⁵D₄ level fit to a single exponential function for the entire pressure range studied. Analyses indicate that the luminescence properties under pressure are more or less reversible, which shows the absence of considerable hysteresis in the present studied glass.