Red luminescence from ZnO: Cr3+ nanophosphors under visible excitation

Abstract

ZnO: Cr3+ (1 mol%) nanophosphor is synthesized by the wet chemical solution combustion method at the temperature of 400°C. Powder X-ray diffraction results confirmed that Cr3+-doped and undoped ZnO nanophosphors exhibit hexagonal wurtzite structure. The average crystallite size calculated from Scherrer-fs method is 25 nm for undoped and 14 nm for Cr3+-doped ZnO. The UV.visible absorption spectra shows red shift in Cr3+-doped ZnO. Photoluminescence studies of undoped ZnO show violet emission peak at 400 nm and blue emission peak at 447 nm. Cr3+-doped ZnO shows red emission peaks at 642, 694 and 746 nm, which are mainly attributed to spin forbidden transitions of 2Eg 4A2g of Cr3+ ion in ZnO: Cr3+ nanophosphor. Thermoluminescence (TL) studies recorded at a heating rate of 6°C s.1 show two well-resolved glow peaks at 124 and 284°C. It is found that the TL intensity increases with the gamma irradiation dose (500 Gy. 10 kGy).