One-step synthesis of ZnO nanosheets: a blue-white fluorophore

Abstract

Zinc oxide is synthesised at low temperature (80°C) in nanosheet geometry using a substrate-free, single-step, wet-chemical method and is found to act as a blue-white fluorophore. Investigation by atomic force microscopy, electron microscopy, and X-ray diffraction confirms zinc oxide material of nanosheet morphology where the individual nanosheets are polycrystalline in nature with the crystalline structure being of wurtzite character. Raman spectroscopy indicates the presence of various defects, while photoluminescence measurements show intense green (centre wavelength approximately 515 nm) blue (approximately 450 nm), and less dominant red (approximately 640 nm) emissions due to a variety of vacancy and interstitial defects, mostly associated with surfaces or grain boundaries. The resulting colour coordinate on the CIE-1931 standard is (0.23, 0.33), demonstrating potential for use as a blue-white fluorescent coating in conjunction with ultraviolet emitting LEDs. Although the defects are often treated as draw-backs of ZnO, here we demonstrate useful broadband visible fluorescence properties in as-prepared ZnO.

Role of zinc interstitials and oxygen vacancies of ZnO in photocatalysis: a bottom-up approach to control defect density

“…Based on this the V þ O state captures an electron from CB and forms a neutral state (V * O ), from which a transition to VB occurs by the emission of green light at a $500 nm wavelength, eqn (4). 16 …”

“…16 The processes described in eqn (4) and (5) occur in the bulk grain region (BGR) and depletion region (DR), respectively.…”

“…4,8 Note that the defects form intermediate bands within the band gap, which allow visible light harvest especially in the case of wide band gap semiconductors. 1,4,8,[15][16][17] The lattice defects connected to PCA are basically intrinsic (vacancies, interstitials, anti-site) or extrinsic (induced by impurities) in nature. 1,4,6,[8][9][10][11][12][13]15,18 However, it is rather hard, though intriguing, to determine which defect is more benecial for PCA, especially in the context of ZnO because controlling the defect density and maintaining a balance among various defect types is quite challenging.…”

“…1,6,[8][9][10][11][12][13] In the context of ZnO, numerous studies deal with V O s, 4,8,10,11,13,21 which is not the case with Zn i s. It is also notable that the balance between the relative densities of Zn i s and V O s is still challenging. 15 The presence of Zn i s and V O s in ZnO can be easily identied by simple photoluminescence (PL) experiments, [15][16][17]27 indicated by blue and green emissions, respectively. Note that studies based on Zn i s are less frequent than V O s because the former defects are difficult to achieve and control in the as-prepared samples.…”

“…Note that studies based on Zn i s are less frequent than V O s because the former defects are difficult to achieve and control in the as-prepared samples. 16,17,[28][29][30][31][32] In contrast, typically synthesized ZnO is predominant with V O s. 4,8,16,17,27,31,32 Consequently, photocatalysis studies involving V O s dominate the literature. 1,4,6,[8][9][10]13,21 In this context, it is very useful and important to study the effect of Zn i s in PCA and their efficiency against V O s. In addition to the fundamental interest, the results of such a study enable an efficient and cost effective design of novel photocatalysts.…”