Enhancing quantum efficiency and tuning photoluminescence properties in far-red-emitting phosphor Ca14Ga10Zn6O35:Mn4+ based on chemical unit engineering

Mn4+ activated Ca14Ga10Zn6O35 (CGZO) have attracted much attention for the usages of white light-emitting-diodes (WLEDs), solar cells and plant growth LEDs. In this paper, we conducted chemical unit engineering in CGZO:Mn4+ by substituting Ge4+-M+ (M = Li, Na, K) for Ga3+-Ca2+. The impacts of Ge4+-M+ (M = Li, Na, K) substitution on the crystal structure, photoluminescence properties, quantum efficiency (QE) and thermal stability were investigated systematically. With the increase of Ge4+-Li+/Na+ and Ge4+-K+, the diffraction peaks moved towards higher and lower angle, respectively. The greatest improvement of emission intensity in Ge4+-Li+/Na+/K+ co-doped CGZO:Mn4+ reached up to 169.4%, 195.0% and 198.9%. Moreover, an obvious red shift (similar to 3.6 nm) was detected in Ge4+-Li+ case and this change was interpreted by Tanabe-Sugano diagram. The IQE and EQE of Ge4+-Li+/Na+/K+ co-doped CGZO:Mn4+ showed remarkable improvements. The highest values of IQE and EQE were found to be 50.9% and 38.9% in Ge4+-K+ incorporated sample. Furthermore, conducting chemical unit engineering in CGZO:Mn4+ could slightly enhance its thermal stability. The configurational coordinated diagram was employed to understand this enhancement comprehensively. Finally, LED devices were fabricated by using Ge4+-Li+ co-doped CGZO:Mn4+ phosphor as light convertor. The excellent electronic luminescence (EL) properties and matchable emission with the absorption of plant pigments demonstrating that these phosphors have promising application in plant growth LED lighting.