First-Principles and Experimental Study of Trace Impurities and Near-Infrared Emission in Alkaline Earth Hexaaluminates

Abstract

First-principles calculations have been performed for bismuth and iron doped into the lattices BaAl12O19 (BAO) and CaAl12O19 (CAO). Experimental data for the optical spectra of CAO at temperatures down to 10 K are presented to support the calculation results. Even undoped samples of CAO exhibit luminescence bands due to trace impurities in the starting materials employed for synthesis. In particular, Mn4+ is ubiquitous. The near-infrared emission band at ∼810 nm in CAO is assigned to Fe3+ at the five-coordinated bipyramidal Al site. The near-ultraviolet emission of Bi-doped CAO is assigned to Bi3+ at the Ca site. The family MAO (M = Ba, Sr, and Ca) has been widely adopted for use as phosphors, when doped with transition metal or lanthanide ions, and the present study highlights the importance of reagent chemical purity in order to avoid energy losses and emission integrity via chemical impurity emissions. The emission wavelength of ∼810 nm presents interesting applications.