Synthesis and optical properties of nanocrystalline ZnO powders by a simple method using zinc acetate dihydrate and poly(vinyl pyrrolidone)

Abstract

This paper reports the synthesis and characterization of nanocrystalline ZnO powders by a simple method using zinc acetate dihydrate and polyvinyl pyrrolidone (PVP) as a chelating agent. The polymeric precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at 600 °C. The precursor was calcined at 600 °C for 1 h to obtain nanocrystalline ZnO powders. The morphology and crystalline size of the calcined powders characterized by SEM and TEM revealed that the powders consisted of the mixture of nanoparticles with particle sizes of ∼50–100 nm and nanorods with diameters of ∼100–200 nm and 200–500 nm in length. The XRD and FT–IR results indicated that the synthesized ZnO powders had the pure wurtzite structure with lattice parameters a and c of 0.32344±0.00058 and 0.51843±0.00211 nm, respectively. The synthesized powders exhibited the UV absorption at around 2.99 eV with the estimated direct bandgap (E_g) of 3.10 eV. Room temperature photoluminescence spectrum of the powders showed a strong UV emission band at ∼2.98 eV, a weak blue band at 2.82 eV, a week blue–green band at 2.56 eV, and a weak green band at 2.34 eV, which indicated their high structural and optical quality.

Introduction

Zinc oxide (ZnO), a representative II–VI compound semiconductor, has attracted considerable attention over the last few years. Its many attractive properties, such as the direct wide bandgap (3.37 eV), large exciton binding energy (60 meV at room temperature), good piezoelectric characteristics, chemical stability and biocompatibility, suggest a host of possible practical applications, notably in the area of ultraviolet/blue emission devices [1], [2], [3], [4], [5], [6], [7], [8]. So far, nanocrystalline ZnO with different particle morphologies and sizes have been obtained by several preparation approaches including thermal decomposition, vapor chemical deposition, sol–gel method, wet chemical synthesis, mechanochemical, electrodeposition, gas-phase reaction, hydrothermal synthesis and so on. An excellent review of recent progress on processing, properties and applications of ZnO was recently published elsewhere [9]. Among other established synthesis methods, simple and cost effective routes to synthesize nanocrystalline ZnO by utilization of cheap, nontoxic and environmentally benign precursors are still the key issues.

In this paper, we report the synthesis and optical properties of nanocrystalline ZnO powders prepared by a simple method using zinc acetate dihydrate and polyvinyl pyrrolidone (PVP) as a chelating agent. The synthesized powders were characterized by TG-DTA, XRD, FT-IR, UV-VIS, SEM, and TEM. The photoluminescence properties of the powders were also investigated.