Photoluminescence Variation With Temperature in ZnO:Ag Nanorods obtained by Ultrasonic Spray Pyrolysis
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Photoluminescence Variation With Temperature in ZnO:Ag Nanorods obtained by Ultrasonic Spray Pyrolysis E. Velázquez Lozada1*, S. Mera Luna2, and L. Castañeda3 1 ESIME – Instituto Politécnico Nacional, México D.F. 07738, México. 2 ESIQE – Instituto Politécnico Nacional, México D.F. 07738, México. 3 ESIME – Ticomán – Instituto Politécnico Nacional, México D.F. 07340, México.
ABSTRACT The photoluminescence, its temperature dependences, as well as structural characteristics obtained by the method of Scanning electronic microscopy (SEM) have been studied in ZnO:Ag nanorods prepared by the ultrasonic spray pyrolysis (USP). PL spectra of ZnO:Ag NRs in the temperature range from 10 K to 300 K are investigated. Three types of PL bands have been revealed: i) the near-band-edge (NBE) emission, ii) defect related emission and iii) IR emission. It is shown that IR emission corresponds to the second-order diffraction of near-band-edge (NBE) emission bands. The study of NBE PL temperature dependences reveals that the acceptor bound exciton (ABE) and its second-order diffraction peak disappeared at the temperature higher than 200 K. The attenuation of the ABE peak intensity is ascribed to the thermal dissociation of ABE with appearing a free exciton (FE). The PL bands, related to the LO phonon replica of FE and its second-order diffraction, dominate in the PL spectra at room temperature that testify on the high quality of ZnO:Ag films prepared by the USP technology. INTRODUCTION Zinc oxide (ZnO) nanocrystals (NCs) with wide band gap energy (3.37 eV) have attracted the great attention due to exceptional exciton properties (high exciton binding energy equal to 60 meV at 300K) and a number of deep levels that emit in the whole visible range and, hence, can provide intrinsic “white” light emission. ZnO NCs are promising candidates for the different optoelectronic devices such as light emitting diodes and lasers [2-7]. The control of the ZnO defect structure in ZnO nanostructures is a necessary step in order to improve the device quality. Since the structural imperfection and defects generally deteriorate the exciton related recombination process, it is necessary to grow the high quality films for the efficient lightemitting applications. The ultrasonic spray pyrolysis (USP) method is a simple, inexpensive, non-vacuum and a low temperature technique for the film synthesis [8]. It will be interesting to study emission of the USP produced ZnO nanostructures doped with Ag versus temperature in order to identify the best regimes for obtaining bright emitting NCs and the nature of optical transitions. EXPERIMENTAL DETAILS ZnO:Ag thin solid films were prepared by the USP technique on the surface of soda-lime glass substrate for the substrate temperatures 4000 C and the different deposition times of 3, 5
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and 10 min. Using this technique the nanoparticle's size can be easily controlled by changing a concentration of starting solution and the atomization parameters. The deposition system includes a piezoelectric transducer operating at v
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