[Photoluminescence of in-doped zinc oxide nanopowders synthesized by precipitation method].

In-doped ZnO nanopowders were prepared by precipitation. The influence of the processing parameters, such as In doping concentration, calcination temperature, reactant ratio and type of precipitant on the grain size, structure and photolumines cence (PL) of In/ZnO nanopowders was detailed analyzed by using X-ray diffraction (XRD) and photoluminescence spectrum. The experimental results indicated that with the increase in the In doping level (the molar ratio of In3+ /Zn2+ increased from 0%. to 5%), the crystallization and the UV emission of ZnO nanopowders were reduced because of the increase of impurity defects. And the UV emission band would have a red-shift from 389 to 419 nm, which could be resulted from the effects of merging of donor and conduction bands, and potential fluctuations of impurity energy level. The calcination temperature will play an important role in synthesis of luminescence materials. When the calcination temperature was raised from 500 to 600 degrees C, the grain size of In/ZnO nanopowder increased gradually, and the dominated UV emission band was improved due to the enhanced crystallization of the nanopowder. If the temperature was raised up to 800 degrees C, the crystallization of the sample was further improved, leading to an enhanced intensity of UV emission Additionally, near this temperature, the oxygen vacancy is easier to be produced owing to the improvement of the kinetic energy for the ions in lattice, which induces in the enhancement of the green emission band peaking at 525 nrn. For the temperature up to 1,000 degrees C, the UV emission band was suppressed due to the production of excessive oxygen vacancy, and the In/ZnO nanopowder exhibited a dominated green emission. The luminescence performance of the In/ZnO nanopowder is also much affected by the reactant ratio. The reaction rate is improved by the increase of the NH4 HCO3 / Zn(NO3)2 molar ratio, which will decrease both grain size of In/ZnO nanopowder and emission intensity of UV band. Furthermore, the effect of the precipitant on the luminescence was examined. It is obviously that the NH4 HCO3 and NaOH precipitants will remarkably affect the crystallization of the precursor powder, but nearly have no effect on the luminescence property of the final nanopowder products.