Crystal Structure and Site Symmetry of Undoped and Eu3+ Doped Ba2 LaSbO6 and BaLaMSbO6 Compounds (M=Mg,Ca): Tuning Europium Site Occupancy to Develop Orange and Red Phosphor

Abstract

Double perovskite antimonates of the type BaLaMSbO₆ (M=Mg, Ca) were synthesized by a standard solid-state route. The compounds were characterized by X-ray crystallography and the structures were refined using Rietveld method. BaLaMgSbO₆ and BaLaCaSbO₆ crystallized in monoclinic space groups (I2/m) and (P2₁ /n), respectively. In both compounds, La occupied the A-site of perovskite, which is 12-coordinated as compared to Ba₂ LaSbO₆ where La ion shifts to the B-site octahedral coordination due to the larger size of Ba as compared with Mg and Ca. The samples were further characterized using FTIR and the frequency of the octahedral vibration is correlated to the electronegativity of the B-site ions. Photoluminescence study of the title compounds and Ba₂ LaSbO₆ was carried out upon doping with 2 atom% Eu³⁺ ion, which confirmed that Eu³⁺ occupies distorted 12-coordinated A-site in BaLaMSbO₆ (M=Mg, Ca) and symmetrical octahedral B-site in Ba₂ LaSbO₆ . Furthermore, the emission spectrum corresponding to each Eu³⁺ ion at different crystal site was successfully isolated through a TRES study. This site selective occupancy of Eu³⁺ ion also has a direct impact on the light emission, which was found to change from orange to red in a dark room in the order Ba₂ LaSbO₆ : Eu→BaLaCaSbO₆ : Eu→BaLaMgSbO₆ : Eu. Such an outcome will have high impact in designing new commercial Eu³⁺ ion doped phosphor materials and tailoring of their optical properties.

Keywords: Antimonates; Double perovskites; FTIR spectroscopy; Phosphor material; Photoluminescence.