Influence of calcination temperature on phase, powder morphology and photoluminescence characteristics of Eu-doped ZnO nanophosphors prepared using sodium borohydride

The prime focus of this work is to synthesize Eu-doped ZnO using sodium borohydride, and analyse the phase formation, functional groups, morphology, elemental mapping and photoluminescence characteristics including emission intensity, R/O ratio, luminescence lifetime, CIE, CCT and colour purity of Eu-doped ZnO phosphors, calcined in a wide range of temperature. XRD analysis confirmed the presence of only ZnO up to 800 degrees C. Minor phases such as EuBO3 and Eu(BO2)(3) were also observed along with the major phase of ZnO at and above 1000 degrees C. FTIR results suggested that the presence of metal-oxygen, borate (BO3 and BO4) and hydroxyl (O-H/B-OH) groups in the as-synthesized sample may help to form EuBO3 and Eu(BO2)(3) phases along with ZnO at higher temperature. Particles were found to be elliptical or elongated rod and polyhedral shape up to 800 degrees C, and it became nearly spherical and dumbbell shape at 1000 degrees C. At high temperature of 1200 degrees C, the particles were consolidated in nature. Nonhomogeneous distribution of Eu3+ ions were observed up to moderate temperature, and it became segregated/clustered in the ZnO matrix at 1200 degrees C, as seen from EDX mapping. The photoluminescence characteristics revealed an intense broad transition of D-5(0) -> F-7(2) at 613 nm for samples calcined up to 800 degrees C. However, a splitting nature in D-5(0) -> F- 7(2) transition was observed for 1000 degrees C and 1200 degrees C samples, due to the non-homogenous distribution of Eu3+-ions along with induced secondary phases. The luminescence decay was analysed with the help of double exponential function, and the average lifetime of the calcined (400 degrees C) sample was found to be similar to 1.43 ns. It was observed that the presence of secondary phases in the calcined (1000 degrees C and 1200 degrees C) samples do not hamper, rather moderately improve the photoluminescence behaviour of Eu-doped ZnO. Based on photoluminescence characteristics results, it may be suggested that the prepared samples might be a feasible material for use as a yellowish-orange, red or deep red-emitting phosphors. (C) 2020 Elsevier B.V. All rights reserved.