Charge compensating effect of alkali metal ions R+ (R = Li, Na, K) on the luminescence enhancement of CaAl11.9P0.1O19.1:Mn4+ red-emitting phosphor

Abstract

A series of novel Mn4+-doped and Mn4+/R+ co-doped (R = Li, Na, K) CaAl11.9P0.1O19.1 red-emitting phosphors were synthesized by high-temperature solid-state reaction, and their crystal structure, luminescence properties and thermal stability were studied in detail. Under the excitation of the optimal wavelength (396 nm), all phosphors exhibit a strong red-light emission, which corresponds to the 2Eg→4A2g transition of Mn4+. The optimal Mn4+ doping concentration was determined to be x = 0.01 in the CaAl11.9-xP0.1O19.1:xMn4+ phosphor, and excessive dopants will cause concentration quenching due to energy transfer interaction between Mn4+ ions. The alkali metal charge compensation ions Li+, Na+ and K+ co-doped with Mn4+ significantly improve the luminescence intensity of CaAl11.89P0.1O19.1:0.01Mn4+ phosphor, where Na+ co-doped phosphor has the strongest luminescence intensity, and K+ co-doped phosphor has the longest luminescence lifetime. Due to the ion radius of charge compensation ion R+ is closest to that of Ca2+ in the host, it is easier to occupy R+ for the Ca2+ lattice site. R+ can eliminate the positive defects caused by Mn4+ replacing with Al3+, thereby keeping charge valance to be neutral. Moreover, Ca0.9Al11.89P0.1O19.1:0.01Mn4+,0.1Na+ phosphor has excellent color purity (97.0%) and quantum yield (60.7%), indicating that the phosphor has potential application prospects for use in white-light-emitting diodes.