Effect of surface defects on the visible emission from ZnO nanoparticles

Abstract

The luminescent property of ZnO nanoparticles prepared using the wet chemical method has been investigated. The ZnO nanoparticles in the range 5–10 nm exhibit hexagonal Wurtzite structure, and the photoluminescence (PL) spectrum at room temperature shows a broad visible luminescence band and insignificant near-bandgap emission. The broad green luminescence is dominant at both room and boiled off liquid-nitrogen temperature, while the ultraviolet band edge emission is strongly quenched. The prepared ZnO nanoparticles have residual intermediate compound on the surface in the form of an acetate group, which acts as defect centers for the emission of green luminescence. A trace amount of zinc hydroxide is observed in one of the samples and is found to further enhance the intensity of the green luminescence. Raman scattering studies on nanoparticles indicate that the acetate/hydroxyl groups are loosely bound on the surface and are not present in the interior of the ZnO crystal structure

Preparation of surface-modified ZnO quantum dots through an ultrasound assisted sol–gel process

“…Also the peak at 2928 can be assigned to the symmetric methylene stretch (-CH 2 ) [27]. The absorption bands around 1100 cm -1 is due to Si-O bands of APTES [26].…”

Synthesis, Self-assembly and Optoelectronic Properties of Monodisperse ZnO Quantum Dots

“…Sol-gel method Sol-gel method, one of the widely used wet chemical methods in synthesizing various nanomaterials [15,[73][74][75], has been used for fabrication of ZnO QDs [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Among a number of reports on fabrication of ZnO QDs over the past decades, sol-gel method was the mostly used one due to its simplicity and cheapness.…”

“…In this method, neither expensive equipments nor harsh conditions are needed. Tokumoto et al and many other research www.intechopen.com Optoelectronic Devices and Properties 218 groups have reported synthesis ZnO QDs at low temperature, i.e., less than 80 0 C [27][28][29][30][31][32]. Meulenkamp has reported a synthetic process with the highest temperature at only room temperature to make as-prepared ZnO QDs at a size of 3-6nm [29].…”

“…After that, aging or heating was performed to obtain solid ZnO QDs from ZnO sol-gels. Figure 1 shows some TEM images of ZnO QDs prepared by Yadav et al [28]. The size of as-prepared ZnO QDs is arranged from 1nm to 5nm.…”

“…By far, various kinds of synthetic approaches have been realized in fabricating such small ZnO QDs, which can be roughly divided into chemical methods and physical methods. Chemical methods involves sol-gel method [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], hydrothermal growth [41][42][43][44], thermal decomposition [45][46][47][48][49][50], electrochemical method [51][52][53][54], while physical methods involves PLA or PLD [55][56][57][58][59], MOCVD [60][61][62][63], sputtering [64][65][66], FSP method [67][68][69][70] and VPT deposition [71,72]. At present, all the methods can be divided into two parts as follow:…”