Structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN2 and ZnGeN2:Mn2+ for field emission displays

Yellowish-orange-emitting ZnGeN2 and orange-red-emitting ZnGeN2:Mn were synthesized by a facile and mild gas-reduction-nitridation reaction at 1153 K under NH3 flow with air-stable raw materials ZnO, GeO2 and MnCO3. The structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN2 doped with or without Mn2+ were systematically investigated. Rietveld refinements show that the as-synthesized samples are obtained as single-phase compounds and crystallize as an orthorhombic structure with a space group of Pna2(1). The actual chemical composition of the as-prepared ZnGeN2 determined by energy dispersive X-ray spectroscopy suggests that the Ge vacancy defects probably exist in the host. The SEM image reveals that the Zn0.99Mn0.01GeN2 particles form aggregates similar to 500-600 nm in size. The diffuse reflection spectrum and photoluminescence excitation spectrum confirm that the band edge absorption of ZnGeN2 at low energy is 3.3 eV (similar to 376 nm). Upon UV light excitation and electron beam excitation, ZnGeN2 gives an intense yellowish-orange emission around 580-600 nm, associated with a deep defect level due to the Ge vacancy defects, and ZnGeN2:Mn shows an intense red emission at 610 nm due to the T-4(1g)((4)G) -> 6A(1g)(S-6) of Mn2+. The unusual red emission of Mn2+ in tetrahedral Zn2+ sites is attributed to the strong nephelauxetic effect between Mn2+ and the surrounding tetrahedrally coordinated nitrogen. The photoluminescence and cathodoluminescence emission colors of ZnGeN2:Mn have a high color purity of similar to 93-98%. These results demonstrate that ZnGeN2:Mn is a novel, promising red-emitting nitride, potentially applicable to field emission displays with brilliant color-rendering properties and a large color gamut. (C) 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.