Structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN 2 and ZnGeN 2:Mn 2+ for field emission displays

Abstract

Yellowish-orange-emitting ZnGeN 2 and orange-red-emitting ZnGeN 2:Mn were synthesized by a facile and mild gas-reduction–nitridation reaction at 1153 K under NH 3 flow with air-stable raw materials ZnO, GeO 2 and MnCO 3. The structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN 2 doped with or without Mn 2+ 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 ZnGeN 2 determined by energy dispersive X-ray spectroscopy suggests that the Ge vacancy defects probably exist in the host. The SEM image reveals that the Zn 0.99Mn 0.01GeN 2 particles form aggregates ∼500–600 nm in size. The diffuse reflection spectrum and photoluminescence excitation spectrum confirm that the band edge absorption of ZnGeN 2 at low energy is 3.3 eV (∼376 nm). Upon UV light excitation and electron beam excitation, ZnGeN 2 gives an intense yellowish-orange emission around 580–600 nm, associated with a deep defect level due to the Ge vacancy defects, and ZnGeN 2:Mn shows an intense red emission at 610 nm due to the 4T 1g( 4G) → 6A 1g( 6S) of Mn 2+. The unusual red emission of Mn 2+ in tetrahedral Zn 2+ sites is attributed to the strong nephelauxetic effect between Mn 2+ and the surrounding tetrahedrally coordinated nitrogen. The photoluminescence and cathodoluminescence emission colors of ZnGeN 2:Mn have a high color purity of ∼93–98%. These results demonstrate that ZnGeN 2:Mn is a novel, promising red-emitting nitride, potentially applicable to field emission displays with brilliant color-rendering properties and a large color gamut.