Efficient deep-red luminescence with high colour purity from Mn4+-doped ZnAl2O4 nanophosphor

This work presents a highly intense deep-red luminescence (710-748 nm) from non-rare earth (Mn4+)-doped zinc aluminate (ZnAl2O4) nanophosphor. The effect of different concentration of Mn (0.3-4%) on structural, morphological, optical properties and luminescence behaviour of ZnAl2O4 nanocrystals are investigated. The Mn-doped ZnAl2O4 nanocrystals were prepared by microwave combustion method with annealing of the sample at 900 degrees C and characterized by different techniques. The pure spinel structure with mean crystallite size 12-35 nm is found. Further, the estimated value of optical band gap E-g (4.5-2.25 eV) is reduced with increasing Mn concentration, due to creation of sub-bands between valence and conduction gap. From photoluminescence (PL) study, PL excitation bands at 353 nm, 375 nm in ultraviolet region referring to (4)A(2g) -> T-4(1g), and bands at 425 nm, 450 nm in visible region referring to (4)A(2g) -> T-2(2g) and (4)A(2g) -> T-4(2g) transitions, respectively, are obtained. PL emission spectra exhibited broad emission band similar to 440-510 nm attributed to host zinc aluminate nanocrystals along with highly intense emission in the deep-red region similar to 710-748 nm accredited to transition from E-2(g) -> (4)A(2g) of Mn4+ dopant ions. Among all concentration, highly intense, 92% colour pure prominent deep-red band at similar to 710 nm is observed for 0.5% Mn4+-doped ZnAl2O4 nanocrystals. It is found that Mn4+ emission centre emits out the deep-red emission and the strong crystal field of Mn4+ in host enhanced the emission. The critical distance, crystal field strength and Racah parameters have been calculated. The possible electronic transitions explained by T-S (Tanabe-Sugano) diagram and concentration quenching mechanism are discussed. The 6.42 ms mean lifetime was found for 0.5% Mn-doped zinc aluminate from PL decay plot. The obtained parameters suggested the potential applications of Mn4+-doped zinc aluminate deep-red nanophosphor for display applications, WLED and for bio-imaging. [GRAPHICS] .