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Spectral features of the near-band-edge photoluminescence (PL) of submicron-sized ZnO crystals such as nanoplatelets, nanowires, and nanorods grown by an ultrasonic spray pyrolysis (USP) technique were investigated. The measurements of time-integrated and time-resolved PL spectra were performed in the temperature range of 8 - 300 K under various excitation densities by using the fourth harmonics (4.66 eV) of a Nd:YAG laser. Exciton-related emission bands were clearly observed in the ZnO crystals having different morphologies. In nanoplatelets, an emission band originating from radiative recombination of donor-acceptor pairs was also found at around 3.17 eV, indicating the existence of acceptor centers. The binding energies of donor and acceptor were about 53 and 200 meV, respectively. In nanowires, the intensity of an emission band peaking at 3.32 eV obeyed a quadratic dependency on the density of excitation. This fact shows that an inelastic exciton-exciton scattering process is efficient in the nanowires because of high crystal quality. (DOI: 10.1143/JJAP.47.541) ZnO, an environment-friendly material, is a promising candidate for exciton-related optoelectronic devices in the ultraviolet region, and it is also applicable to the devices based on reduced dimensional quantum effect because it can be grown in various crystalline forms with submicron size such as whiskers, nanobelts, nanorods, nanowires, nano- platelets, and so on. In the previous paper, we reported on direct fabrication of single crystalline ZnO submicron structures called nanoplatelets, nanowires, and nanorods by an economically viable ultrasonic spray pyrolysis (USP) technique.1) Utilizing this method, significant changes of the crystal morphologies were realized in a controllable manner by adjusting the nature of precursor solution and the growth temperature. The present paper is concerned with the photolumines- cence (PL) properties of submicron-sized ZnO crystals prepared by USP. In nanoplatelets, the existence of acceptor centers is revealed from the observation of donor-acceptor pair luminescence. An inelastic exciton-exciton scattering process is confirmed in nanowires. Based on these results, we discuss the crystal quality of our submicron-sized ZnO crystals.

Photoluminescence Properties and Morphologies of Submicron-Sized ZnO Crystals Prepared by Ultrasonic Spray Pyrolysis