Identification of the transition responsible for the visible emission in ZnO using quantum size effects

Dijken, A. van; Meulenkamp, Eric A.; Vanmaekelbergh, Daniël; Meijerink, Andries

doi:10.1016/s0022-2313(99)00599-2

Cited by 536 publications

(421 citation statements)

References 14 publications

Supporting

Mentioning

372

Contrasting

Unclassified

Order By: Relevance

“…Hence the emission from the CSHJs is mainly due to the shell region of the heterojunctions, where the visible emission occurs from the surface recombination. 41,60,61 In both the cases, a largely similar visible emission indicates a dominant defect density such as V O s. Importantly, despite the visible emission peaks appearing at almost the same wavelength for both the CSHJs, the energetic location of the V O s for TiO 2 and ZnO are not the same. These spectra will be discussed independently with reference to the plausible defects in the following sections and subsequently juxtaposed with the PCA.…”

Section: Photocatalytic Activity Of Core-shell Heterojunction Nanobersmentioning

confidence: 90%

“…The defects and related emission from the 'shell' region are schematized on the image. In the bulk grain region (BGR) 60 and in the depletion region (DR) 61 respectively. We have not considered the possible emission from the interface, as the oxide hetero-interfaces are not completely understood yet.…”

Section: Photocatalytic Activity Of Core-shell Heterojunction Nanobersmentioning

confidence: 99%

See 1 more Smart Citation

Selective isolation of the electron or hole in photocatalysis: ZnO–TiO2 and TiO2–ZnO core–shell structured heterojunction nanofibers via electrospinning and atomic layer deposition

et al. 2014

View full text Add to dashboard Cite

Heterojunctions are a well-studied material combination in photocatalysis studies, the majority of which aim to improve the efficacy of the catalysts. Developing novel catalysts begs the question of which photo-generated charge carrier is more efficient in the process of catalysis and the associated mechanism. To address this issue we have fabricated core-shell heterojunction (CSHJ) nanofibers from ZnO and TiO 2 in two combinations where only the 'shell' part of the heterojunction is exposed to the environment to participate in the photocatalysis. Core and shell structures were fabricated via electrospinning and atomic layer deposition, respectively which were then subjected to calcination. These CSHJs were characterized and studied for photocatalytic activity (PCA). These two combinations expose electrons or holes selectively to the environment. Under suitable illumination of the ZnO-TiO 2 CSHJ, e/h pairs are created mainly in TiO 2 and the electrons take part in catalysis (i.e. reduce the organic dye) at the conduction band or oxygen vacancy sites of the 'shell', while holes migrate to the core of the structure. Conversely, holes take part in catalysis and electrons diffuse to the core in the case of a TiO 2 -ZnO CSHJ. The results further revealed that the TiO 2 -ZnO CSHJ shows $1.6 times faster PCA when compared to the ZnO-TiO 2 CSHJ because of efficient hole capture by oxygen vacancies, and the lower mobility of holes.

show abstract

Section: Photocatalytic Activity Of Core-shell Heterojunction Nanobersmentioning

confidence: 90%

Section: Photocatalytic Activity Of Core-shell Heterojunction Nanobersmentioning

confidence: 99%

Selective isolation of the electron or hole in photocatalysis: ZnO–TiO2 and TiO2–ZnO core–shell structured heterojunction nanofibers via electrospinning and atomic layer deposition

et al. 2014

View full text Add to dashboard Cite

show abstract

“…From eqn (1) to (5), it appears that both the Zn i and V O s can form ionized levels; however, in the earlier explanation by Zeng et al 15 there is no discussion on charged zinc interstitials forming defect bands within the band gap. In clear contrast to this, V O s form two defect levels 17,27,64,65 within the band gap by following the eqn (4) and (5). Among these two bands, although one is not directly accessible for PCA, it shows an indirect effect by capturing an electron from CB.…”

Section: View Article Onlinementioning

confidence: 99%

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

et al. 2014

View full text Add to dashboard Cite

Oxygen vacancies (V O s) in ZnO are well-known to enhance photocatalytic activity (PCA) despite various other intrinsic crystal defects. In this study, we aim to elucidate the effect of zinc interstitials (Zn i ) and V O s on PCA, which has applied as well as fundamental interest. To achieve this, the major hurdle of fabricating ZnO with controlled defect density requires to be overcome, where it is acknowledged that defect level control in ZnO is significantly difficult. In the present context, we fabricated nanostructures and thoroughly characterized their morphological (SEM, TEM), structural (XRD, TEM), chemical (XPS) and optical (photoluminescence, PL) properties. To fabricate the nanostructures, we adopted atomic layer deposition (ALD), which is a powerful bottom-up approach. However, to control defects, we chose polysulfone electrospun nanofibers as a substrate on which the non-uniform adsorption of ALD precursors is inevitable because of the differences in the hydrophilic nature of the functional groups. For the first 100 cycles, Zn i s were predominant in ZnO quantum dots (QDs), while the presence of V O s was negligible. As the ALD cycle number increased, V O s were introduced, whereas the density of Zn i remained unchanged. We employed PL spectra to identify and quantify the density of each defect for all the samples. PCA was performed on all the samples, and the percent change in the decay constant for each sample was juxtaposed with the relative densities of Zn i s and V O s. A logical comparison of the relative defect densities of Zn i s and V O s suggested that the former are less efficient than the latter because of the differences in the intrinsic nature and the physical accessibility of the defects. Other reasons for the efficiency differences were elaborated.

show abstract

“…1) [3,4]. In some wide band gap semiconductors, significant luminescence can even be observed in undoped materials due to the presence of intrinsic defects [20][21][22][23]. While rare-earthdoped materials are currently employed commercially, there are a number of issues associated with supply, toxicity, and non-radiative surface recombination at surfaces which are problematic [2,24,25].…”

Section: Introductionmentioning

confidence: 99%

Surface-specific visible light luminescence from composite metal oxide nanocrystals

et al. 2015

View full text Add to dashboard Cite

Low-coordinated surface elements on metal oxide nanoparticles represent the basis for a new concept of luminescent nanoparticles made of abundant, non-toxic, and thermally stable materials. This combined experimental and theoretical study describes the generation and stability of Ba-doped MgO nanoparticle surfaces and their optical absorption and luminescence dependence on Ba loading. It is demonstrated that the vapor phase growth process employed here represents a particularly robust synthesis approach for particle powders with reproducibly adjustable photoluminescence emission properties in the range between blue and yellow light. Moreover, this indepth characterization also provides an understanding of the electronic and optical characteristics of this nanoparticulate material with a so far unnoticed potential for solidstate light applications that are based on down conversion of UV light.

show abstract

Identification of the transition responsible for the visible emission in ZnO using quantum size effects

Cited by 536 publications

References 14 publications

Selective isolation of the electron or hole in photocatalysis: ZnO–TiO2 and TiO2–ZnO core–shell structured heterojunction nanofibers via electrospinning and atomic layer deposition

Selective isolation of the electron or hole in photocatalysis: ZnO–TiO2 and TiO2–ZnO core–shell structured heterojunction nanofibers via electrospinning and atomic layer deposition

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

Surface-specific visible light luminescence from composite metal oxide nanocrystals

Contact Info

Product

Resources

About