Strong Green Photoluminescence in Zr 3 N 4 Thin Films with an Orthorhombic Structure

Green light causes the maximum luminous sensation in human eyes, which will bring many advantages for potential uses. However, the efficiency of light-emitting diodes (LEDs) in the green wavelength range (495-570 nm) is much lower than that in red or blue regions, which is known as the "green gap" problem. In this study, we report the strong green photoluminescence in metastable Zr 3 N 4 thin films with orthorhombic structure for the first time. Crystallized Zr 3 N 4 thin films have been successfully grown by high-power impulse magnetron sputtering. Notable green photoluminescence in the wavelength region of 490-535 nm has been identified in such orthorhombic Zr 3 N 4 thin films even at room temperature. In addition, a joint experimental and theoretical study has been performed to investigate its electronic structures and to reveal the origins of such green light emissions. The calculations of the transition dipole moments demonstrate that the direct transition between the conduction band minimum and the energy level II below the valence band maximum are responsible for such strong green photoluminescence. This work may pave a new way to solve to the "green gap" problem in LEDs with low cost.