Achieving highly efficient far-red emission from luminescence-ignorable Ca2MgTeO6:Mn4+ to Ca2-zLnzMgTe1-yWyO6:Mn4+ (Ln = La, Y, Gd) phosphors via solid solution and impurity doping strategies

Abstract

The Mn4+-doped Ca2MgTeO6 (CMTO) far-red emitting phosphors with double perovskite-type structure were successfully synthesized. Upon near-ultraviolet (n-UV, 300 nm) light excitation, the as-prepared phosphors showed far-red light at 700 nm attributed to the 2Eg→4A2g transition of Mn4+ ion. The doping concentration of the CMTO:xMn4+ samples was optimized to be 0.8 mol%. The relevant mechanism of concentration quenching was demonstrated as the dipole-dipole interaction. Furthermore, solid solution and impurity doping strategies were adopted to improve the far-red emission of the luminescence-ignorable CMTO:Mn4+ phosphor. Series of Ca2MgTe(1−y)WyO6:0.8 mol%Mn4+ (y = 0–100 mol%) solid solution and Ca2−zLnzMgTe0.6W0.4O6:Mn4+ (Ln = La, Y, and Gd, z = 10 mol%) phosphors were synthesized through the above two strategies. The luminescence intensity of the optimal Ca1.9Gd0.1MgTe0.6W0.4O6:Mn4+ phosphor was 13.7 times that of the CMTO:Mn4+ phosphor and 2.51 times that of red commercial phosphor K2SiF6:Mn4+. Notably, both CMTO:Mn4+ and Ca1.9Gd0.1MgTe0.6W0.4O6:Mn4+ phosphors exhibited remarkable thermal stability compared with most Mn4+-doped phosphors. Finally, the highly efficient Ca1.9Gd0.1MgTe0.6W0.4O6:Mn4+ phosphor was successfully applied in fabricating the warm white light diode (w-LED). This working along both lines strategy exhibited great potential for luminescence optimization of Mn4+-doped oxide phosphors.