Red photoluminescence and band edge shift from ZnO thin films

Marotti, Ricardo E.; Badan, J.; Quagliata, E.; Dalchiele, Enrique A.

doi:10.1016/j.physb.2007.04.038

Cited by 16 publications

(9 citation statements)

References 15 publications

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“…This is usually called the “orange” PL band 32, because this is the color that it appears to the eye. This room temperature PL is typical of samples prepared by electrochemical deposition 58. Its origin is due to the presence of defect states: both shallow donors and deep acceptors, related to zinc interstitials and oxygen vacancies 58.…”

Section: Resultsmentioning

confidence: 90%

Zinc‐oxide nanowires electrochemically grown onto sol–gel spin‐coated seed layers

Bojorge

Kent

Téliz

et al. 2011

Physica Status Solidi (a)

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Phone: þ598 2 711 09 05, Fax: þ598 2 711 16 30The electrochemical deposition of ZnO nanowires (NW) was optimized by growing onto a previously deposited seed layer. The ZnO seed layer was prepared by a sol-gel process from different precursor solutions and deposited onto FTO/glass by spin coating. Afterwards, NW were electrochemically grown onto those seed layers. The electrolyte was an aqueous solution of the Zn þ2 precursor (1 mM zinc acetate) and a supporting electrolyte (0.1 M sodium acetate), saturated with bubbling oxygen. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical transmittance. The XRD measurements show typical diffraction pattern of ZnO wurtzite structure. The SEM micrographs show the presence of smooth NW with hexagonal sections with diameters ranging from 40 to 250 nm. The optical transmittance reveals the presence of ZnO with bandgap energy between 3.23 and 3.29 eV. These spectra show a monotonically increasing transmittance from the UV into the red part of the spectrum. This feature may be originated in the dispersion of light at the NW and can be used to enhance below-gap absorption.

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Section: Resultsmentioning

confidence: 90%

Zinc‐oxide nanowires electrochemically grown onto sol–gel spin‐coated seed layers

Bojorge

Kent

Téliz

et al. 2011

Physica Status Solidi (a)

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“…V O Zn i as the lower state in red/yellow PL. More recently, though, a systematic shift of the red emission wavelength with the UV band edge absorption (dependent on different ZnO thin film preparations) led Marotti et al [45] to suggest a radiative transition from an upper state that is referenced to the conduction band, possibly Zn i , to a deep level where V O is again suggested. However, in their work, this process does not seem to persist above approximately 200 K, and so we are left with the link to surface oxygen to account for the red emission.…”

Section: Resultsmentioning

confidence: 99%

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

2012

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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.

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“…As noted above, we collected a large number of published Tauc analyses of undoped ZnO that included plots of the absorbance data against the photon energy . This was critical, as our assessment of the application of the Tauc method required the consistent application of a fitting method, as described below.…”

Section: Modelmentioning

confidence: 99%

Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

Viezbicke

Patel

Davis

et al. 2015

Phys. Status Solidi B

896

419

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One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near‐edge region can be fitted to a simple expression in which the intercept gives the band‐gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called “Tauc” plots). While the technique is powerful and simple, the accuracy of the fitted band‐gap result is seldom stated or known. We tackle this question by refitting a large number of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examination of the band gap values and their distribution leads to a discussion of some experimental factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure‐of‐merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single crystalline material.

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Red photoluminescence and band edge shift from ZnO thin films

Cited by 16 publications

References 15 publications

Zinc‐oxide nanowires electrochemically grown onto sol–gel spin‐coated seed layers

Zinc‐oxide nanowires electrochemically grown onto sol–gel spin‐coated seed layers

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

Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

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