Size dependent fluorescence spectroscopy of nanocolloids of ZnO

Abstract

Intra-excitonic relaxation dynamics in ZnO Appl. Phys. Lett. 99, 231910 (2011) Thermal diffusion of nitrogen into ZnO film deposited on InN/sapphire substrate by metal organic chemical vapor deposition J. Appl. Phys. 110, 113509 (2011) Manifestation of spin-spin interaction between oxygen vacancy and magnesium in ZnMgO nanorods by electron paramagnetic resonance studies Appl. Phys. Lett. 99, 194101 (2011) Selective pair luminescence in the 1.4-eV band of CdTe:In J. Appl. Phys. 110, 093103 (2011) Evidence of cation vacancy induced room temperature ferromagnetism in Li-N codoped ZnO thin films Appl. Phys. Lett. 99, 182503 (2011) Additional information on J. Appl. Phys. In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet ͑UV͒ emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.

Structural and optical characterization of pure and starch-capped ZnO quantum dots and their photocatalytic activity

“…5 shows the UV absorption spectrum (UV-VIS-NIR spectrophotometer, Shimatzu 3600 model) of pure ZnO (a) and ZnO/starch (b) QDs, the direct band to band transition has occurred and their calculated corresponding bandgap energy values was approximately 3.8 eV (320 nm) calculated using E = hc/k formula. A similar observation was also found by the previous reports (Irimpan et al 2007;Klingshirn 2007), which hold well with our results. In the case of ZnO/starch QDs, a little red shift and enhanced absorption was observed in the peak position when compared with ZnO QDs.…”

Synthesis and Characterizations of Zinc Oxide Nanoparticles for Antibacterial Applications

“…On the other hand broad band in the visible emission spectra were observed at 455 nm for precursor ZnCl 2 , 450, 466 481 and 492 nm for Zn(NO 3 ) 2 .6H 2 O) and 435, 469 nm , Zn (CH 3 COO) 2 .2H 2 O respectively. The visible emission spectra are related to the transition of electron from deep donor level to valence band due to oxygen vacancies and the transition from conduction band to deep acceptor level due to impurities and defect states [35]. The well known stronger and broader emission situated in the UV to blue green emission suggested that the obtained ZnO NPs are high purity and crystalline.…”

“…It is well known that there are two kinds of emission bands of UV and visible spectra in ZnO crystal. The emission in the UV region is attributed to the recombination between electrons in the conduction band and holes in the valance band [35]. The UV emission of ZnO NPs synthesised from precursors, ZnCl 2 and Zn (NO 3 ) 2 .6H 2 O observed at 325, 392 nm respectively.…”

Enhanced Stability of Organic Photovoltaics by Additional ZnO Layers on Rippled ZnO Electron-collecting Layer using Atomic Layer Deposition

“…Broad features could be found for each spectrum between 450-850 nm, which correspond to the states of surface defects of ZnO such as oxygen vacancies. 21,22 It is well known that these surface defects of ZnO can act as recombination center of electron-hole pairs, and lead to the reduction in performance of photovoltaics consisting of ZnO as electron-collecting layers. 21,22 Area of the broad PL features of each spectrum should be proportional to the number of defect sites of ZnO in each sample.…”

“…21,22 It is well known that these surface defects of ZnO can act as recombination center of electron-hole pairs, and lead to the reduction in performance of photovoltaics consisting of ZnO as electron-collecting layers. 21,22 Area of the broad PL features of each spectrum should be proportional to the number of defect sites of ZnO in each sample. From data taken from freshly prepared samples, one can notice that the PL peak intensity was significantly reduced by additional ALD-ZnO deposition (Figs.…”