Emission of ZnO:Ag nanorods obtained by ultrasonic spray pyrolysis E. Velázquez Lozada a,n , T.V. Torchynska b , J.L. Casas Espinola b , B. Pérez Millan c a Q1 ESIME – Instituto Politécnico Nacional, México D.F. 07738, Mexico b ESFM – Instituto Politécnico Nacional, México D.F. 07738, Mexico c UPIITA – Instituto Politécnico Nacional, México D.F. 07738, Mexico article info Keywords: SEM XRD Photoluminescence ZnO:Ag nanorods Acceptor bound exciton abstract Scanning electronic microscopy (SEM), X ray diffraction (XRD), photoluminescence (PL) and its temperature dependence have been studied in ZnO:Ag nanorods (NRs) prepared by the ultrasonic spray pyrolysis (USP) method. The time variation at the growth of ZnO:Ag films permits modifying the ZnO phase from the amorphous to crystalline, to change the size of ZnO:Ag NRs and to vary their emission spectra. PL spectra of ZnO:Ag NRs versus temperature has been investigated. This study reveals that the PL band related to the acceptor Ag Zn (LO phonon replicas of an acceptor bound exciton, ABE (2.877 eV)), and its second-order diffraction peak (1.44 eV) disappeared in the temperature range of 10–170 K with the formation of free exciton (FX). The PL intensity of defect related PL bands decreases monotonously in the range 10–300 K with the activation energy of 13 meV. The PL band (3.22 eV), related to the LO phonon replica of free exciton (FX-2LO) and its second-order diffraction peak (1.61 eV) increase monotonously in the range 10–300 K. FX related peak dominates in PL spectra at room temperature that testifies on the high quality of ZnO:Ag films prepared by the USP technology. & 2014 Published by Elsevier B.V. 1. Introduction Nanocrystalline zinc oxide (ZnO) with wide band gap energy nearly 3.37 eV, the high exciton binding energy (60 meV at 300 K) and easy way of nanostructure preparation has attracted great attention during the last two decades [1]. In addition to excep- tional exciton properties in ZnO exists a number of deep levels that emit in the whole visible range and, hence, can provide intrinsic “white” light emission. ZnO nanostructures are being investigated as promising candidates for different optoelectronic applications, such as the non-linear optical devices [2], light-emitting devices [3–6], transparent electrodes for solar cells [7] and laser diodes [8], as well as for the excellent field emitters [9], electrochemical sensors and toxic gas sensors [10]. The design of new electronic devices requires the development of a new generation of nanos- tructures. ZnO has been synthesized as nanowires, nanoribbons, nanorods, nanosheets, nanotubes and nanowalls [11]. The control of ZnO defects in nanostructures is an important step in order to improve the device quality. Note that the exciton related emission is very intensive in the bulk ZnO but, as a rule, this emission is difficult to see in ZnO nanocrystals. Since the structural imperfec- tion and defects generally deteriorate the exciton related recom- bination process, it is very important task to grow the high quality films for efficient light-emitting applications. To obtain the high ZnO film quality, various techniques have been employed such as molecular beam epitaxy (MBE) [12], pulse laser deposition (PLD) [13], or metal-organic chemical vapor deposition (MOCVD) [14]. Mentioned methods are expensive and require a high vacuum. In comparison with these methods, the ultrasonic spray pyrolysis (USP) is a simple, inexpensive, non-vacuum and a low temperature technique for the film synthesis [15]. This process offers many advantages such as easy compositional modifications Q2 , easy intro- duction of various functional groups and impurities, relatively low annealing temperatures and the possibility of the deposition on a large area substrate. This paper presents the study of ZnO:Ag nanorods (NRs) prepared by USP using the scanning electronic microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) methods. 2. Experimental details ZnO:Ag thin solid films were prepared by the USP technique (Fig. 1) on the surface of soda-lime glass substrate at the substrate temperature 400 1C and different deposition times (Table 1). Using this technique the nanoparticle's size can be easily controlled by changing the concentration of starting solution and the atomization parameters. The deposition system presented in Fig. 1 includes a piezoelectric transducer operating at variable frequencies up to 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B http://dx.doi.org/10.1016/j.physb.2014.04.083 0921-4526/& 2014 Published by Elsevier B.V. n Corresponding author. Tel.: þ52 5557296000x55031. E-mail address: evlozada5@yahoo.com.mx (E. Velázquez Lozada). Please cite this article as: E. Velázquez Lozada, et al., Physica B (2014), http://dx.doi.org/10.1016/j.physb.2014.04.083i Physica B ∎ (∎∎∎∎) ∎∎∎–∎∎∎