LiBa₁₂(BO₃)₇F₄ (LBBF) crystals doped with Eu³⁺, Tb³⁺, Ce³⁺: structure and luminescence properties

The luminescent properties of single crystals and polycrystalline samples of LiBa₁₂(BO₃)₇F₄ (LBBF) doped and co-doped with Eu³⁺, Tb³⁺, and Ce³⁺ have been studied in order to disclose their potential for application in white light-emitting diodes. Deciphering of LBBF:Eu³⁺ crystal structure (P4₂/mbc) makes it possible to determine the scheme of heterovalent isomorphic substitution 3Ba²⁺ ← 2Eu³⁺ + □, □ - vacancy in barium sites. Luminescent properties of LBBF crystals co-doped with Eu³⁺, Tb³⁺, Ce³⁺ and Eu³⁺, Tb³⁺ are compared. Both crystals demonstrate the luminescence close to day light with CIE coordinates and correlated color temperature (0.280; 0.305), 9232 K for LBBF:Eu³⁺,Tb³⁺,Ce³⁺ and (0.353; 0.390), 4849 K for LBBF:Eu³⁺,Tb³⁺ at 300 K at 370 nm excitation. The study of polycrystalline samples LBBF:Ce³⁺, LBBF:Tb³⁺, and LBBF:Eu³⁺, using X-ray diffraction, shows that the homogeneity regions of solid solutions differ significantly. In solid solutions LBBF:Tb³⁺ and LBBF:Eu³⁺, a gradual change in symmetry in the "tetragonal → orthorhombic → tetragonal" series takes place as the concentration of the dopant increases. When excited at a wavelength 395 nm, LBBF:Eu³⁺ samples with the content of Eu³⁺ 0.5 wt% and 2 wt% demonstrate intense red light with a high quantum yield of 63 and 60%, respectively, which allows them to be used as red components of composite phosphors for white LEDs.