A Photoluminescence Study of Eu3+, Tb3+, Ce3+ Emission in Doped Crystals of Strontium-Barium Fluoride Borate Solid Solution Ba4- xSr3+ x(BO3)4- yF2+3 y (BSBF)

Abstract

The present study is aimed at unveiling the luminescence potential of Ba_4-xSr_3+x(BO₃)_4-yF_2+3y (BSBF) crystals doped with Eu³⁺, Tb³⁺, and Ce³⁺. Owing to the incongruent melting character of the phase, the NaF compound was used as a solvent for BSBF crystal growth. The structure of BSBF: Eu³⁺ with Eu₂O₃ concentration of about 0.7(3) wt% was solved in the non-centrosymmetric point group P6₃mc. The presence of Eu₂O₃ in BSBF: Eu³⁺ leads to a shift of the absorption edge from 225 nm to 320 nm. The photoluminescence properties of the BSBF: Ce³⁺, BSBF: Tb³⁺, BSBF: Eu³⁺, and BSBF: Eu³⁺, Tb³⁺, Ce³⁺ crystals have been studied. The unusual feature of europium emission in BSBF is the intensively manifested ⁵D₀→⁷F₀ transition at about 574 nm, which is the strongest for BSBF: Eu³⁺ at 370 nm excitation and for BSBF: Eu³⁺, Tb³⁺, Ce³⁺ at 300 nm and 370 nm excitations. No evidence of Tb³⁺→Eu³⁺ energy transfer was found for BSBF: Eu³⁺, Tb³⁺, Ce³⁺. The PL spectra of BSBF: Eu³⁺ at 77 and 300 K are similar with CIE chromaticity coordinates of (0.617; 0.378) at 300 nm excitation and (0.634; 0.359) at 395 nm excitation and low correlated color temperature which implies application prospects in the field of lightning. Due to the high intensity of ⁵D₀→⁷F₀ Eu³⁺ transition at 370 nm excitation, the BSBF: Eu³⁺ emission is yellow-shifted.

Keywords: borates; dopants; photoluminescence; rare-earth elements.