Complex crystal structure and photoluminescence of Bi3+-doped and Bi3+/Eu3+ co-doped Ca7Mg2Ga6O18

Abstract

Recently, broad-band white-light-emitting using Eu²⁺, Ce³⁺, or Bi³⁺ in multi-sites of a single-phase phosphor have drawn extensive attention due to their potential to realize high-quality indoor lighting. This work reports a novel oxide, Ca₇Mg₂Ga₆O₁₈ (CMG), possessing a complex crystal structure in the space group F432. Rietveld refinements of high-resolution synchrotron X-ray diffraction data were performed to determine the accurate atomic positions and occupancy factors, giving a reasonable composition of Ca₇Mg_1.91(4)Ga_6.09(4)O₁₈. Due to the multiple sites of Ca²⁺, which are suitable for the doping of Bi³⁺ activators, CMG is a promising host to achieve broad-band white-light emission. Detailed structural and spectroscopic analyses revealed that the Bi³⁺-activator shows multiple and site-selective occupancy, which is the origin of the red-shifts in both broad-band excitation and emission spectra upon increasing the Bi³⁺ content. A series of Bi³⁺ and Eu³⁺ codoped phosphors with tunable blue-pink-red emission were prepared due to the Bi³⁺-to-Eu³⁺ energy transfer. Due to the distinctive thermal behaviors of Bi³⁺ and Eu³⁺ emissions, CMG:Bi³⁺,Eu³⁺ is a candidate for optical thermometry.