RESEARCH ARTICLE Copyright © 2008 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 8, 1–7, 2008 LowTemperaturePhotoluminescenceCharacteristicsof ChemicallySynthesizedIndiumDoped Zinc Oxide Nanostructures A. Escobedo Morales 1 , R. Aceves 2 , U. Pal 1 ∗ , and J. Z. Zhang 3 1 Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Postal J-48, CP 72570, Puebla, Pue., México 2 Centro de Investigación en Física, Universidad de Sonora, Apdo Postal: 5-48, CP 83190, Hermosillo, Sonora, México 3 Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA Photoluminescence (PL) emission and excitation (EPL) spectra of un-doped and indium (1%) doped 1D zinc oxide nanostructures are studied at different temperatures. The nanostructures reveal a blue emission band attributed to localized donor states. Indium doping enhances the blue emission. While at low temperatures (<50 K) PL spectra are dominated by the emission attributed to the recombination of excitons bound to neutral donors (D 0 ,X), at higher temperatures (>100 K), defect related emissions in the visible range dominate over the excitonic emission. Temperature depen- dence measurements on the doped sample reveal that (D 0 ,X) emission energies obey the Varshni’s formula with fitting constants  = 84 ± 03 × 10 −4 eV/K and  = 650 ± 40 K. The (D 0 ,X) emission intensity decays exponentially with temperature. Keywords: Zinc Oxide, Nanostructures, Indium-Doping, Photoluminescence. 1. INTRODUCTION Throughout the last decade, the interest on light emit- ting semiconductors with a wide band gap was focused on GaN. 1 However, in recent years considerable effort has been made to develop a new generation of opto- electronic devices based on II–VI semiconductors. In this regard, zinc oxide (ZnO) has been one of the most promis- ing compounds, due to its desirable electronic properties like a direct band gap of 3.37 eV at room temperature, 2 and larger exciton binding energy (60 meV) 3 than GaN (25 meV). 4 Since its exciton binding energy is beyond the thermal energy at room temperature (25 meV), 5 it opens up the possibility to obtain ultraviolet lasing response with- out the necessity of cryogenic temperatures or high exci- tation energies. 6 Nevertheless, high quality crystals are required to generate the lasing effect. Scientists believe that an alternative route to obtain higher optical emissions is using doped semiconductor nanostructures, as these low-dimensional materials facilitate lasing effect due to enhanced density of states near their band edges. 7 There- fore, efforts to incorporate shallow states in the elec- tronic band structure of ZnO bulk and nanostructures by introducing doping atoms in the host lattice have ∗ Author to whom correspondence should be addressed. been carried out. 8–10 It is well known that upon doping, structural defects that appear in the lattice could result in radiative or non-radiative centers in the nanostructures. Beside the extrinsic defects, the effect of native defects on the luminescent properties of ZnO structures has been extensively studied. 11–13 Nevertheless, not all its optical characteristics are clear, and there is still controversy on the origin of visible emissions in their luminescence spec- tra. By far, the green luminescence band is the most com- mon visible emission observed in bulk ZnO, and has been attributed to the single ionized oxygen vacancies V 0 o . 14 On the other hand, yellow, red, and blue emissions have also been observed in undoped zinc oxide, 15 and their origin still requires further studies. Here we report the photoluminescence of undoped and indium doped rod-like zinc oxide nanostructures grown by hydrothermal technique. Distinct temperature and exci- tation evolution of the donor bound exciton (D 0 ,X), and blue emissions in undoped and doped nanostructures are observed. On the basis of the observed results, possible mechanisms for such emissions are discussed. 2. EXPERIMENTALDETAILS Undoped and indium doped zinc oxide nanostructures were obtained by hydrolysis in an alkaline aqueous J. Nanosci. Nanotechnol. 2008, Vol. 8, No. 11 1533-4880/2008/8/001/007 doi:10.1166/jnn.2008.016 1