Temperature Control of Yellow Photoluminescence from SiO2-Coated ZnO Nanocrystals (original) (raw)
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We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix.
Journal of Physics and Chemistry of Solids, 2013
ZnO-SiO 2 nanocomposite consisting of ZnO nanostructures grown in SiO 2 (silica) host matrix was obtained via hydrolysing Tetraethylorthosilicate (TEOS) with ethanolic solution of Zinc nitrate hexahydrate using Sol-gel method. Systematic study of the key parameters (precursor, concentration, and heat treatment conditions) has been taken into account that influences the growth mechanism and morphology of the as formed nanostructures. X-ray diffraction (XRD) analysis was used to determine the crystallinity, particle size and lattice parameter. Scanning electron microscopy (SEM) of the sample reveals the formation of ZnO nanostructures in silica matrix. Room temperature Photoluminescence (PL) measurement of the sample was done to understand the nature of possible defect level transition responsible for visible and rarely observed orange-red emissions in ZnO. This study reveals the usefulness of the nanocomposites as a luminescent material.
High thermal annealing effect on structural and optical properties of ZnO–SiO2 nanocomposite
Materials Science in Semiconductor Processing, 2014
The effect of annealing temperature on photoluminescence (PL) of ZnO-SiO 2 nanocomposite was investigated. The ZnO-SiO 2 nanocomposite was annealed at different temperatures from 600 1C to 1000 1C with a step of 100 1C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO 2 matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 1C and dumbbell morphology above 800 1C. The absorption spectrum of ZnO-SiO 2 nanocomposite suffers a blue-shift from 369 nm to 365 nm with increase of temperature from 800 1C to 1000 1C. The PL spectrum of ZnO-SiO 2 nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 1C to 700 1C and then decreased for samples annealed at and above 800 1 C. The XRD results showed that formation of willemite phase starts at 800 1C and pure willemite phase formed at 1000 1C. The decrease of the intensity of 396 nm emission peak at 900 1C and 1000 1C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO 2 at these temperatures. At 1000 1C, an emission peak at 388 nm is observed in addition to UV emission of ZnO at 396 nm and is believed to be originated from the willemite.
ZnO nanoparticles (ZnO–NPs) were synthesized using sol–gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). In this study, the effects of annealing temperature on photoluminescence (PL) of ZnO-NPs were studied. ZnO was annealed at various temperatures between 500 and 800 °C. The X-ray diffraction (XRD) results demonstrated that grain size increased with increase of annealing temperature. The average size of the nanoparticles was determined by SEM as well as XRD data and found to be 50 nm after annealing at 800 °C. As the annealing temperature increased from 500 to 800 °C, the intensities of both UV peak and that of green luminescence (GL) enhanced monotonously. The enhancement in the UV peak intensity is attributed to the decrease of grain boundaries and surface states; whereas, the remarkable improvement in the GL is assigned to the out-diffusion of oxygen from the sample up to 800 °C. It supports that GL is induced by the singly ionized oxygen vacancies. These oxygen vacancies are saturated due to the finiteness of the defects at 800 °C.
Photoluminescence in Si/ZnO nanocomposites
Materials Science and Engineering: B, 2004
Composite films of Si and ZnO were prepared by r.f. co-sputtering technique with different Si contents. Photoluminescence (PL) and Raman spectroscopy were used to characterize the films. Transmission electron microscopy revealed that the Si dispersed in the ZnO matrix form nano-particles of size ranging from 2 to 4 nm. On thermal annealing at and above 700 • C, the nano-particles aggregated to form micro-crystals. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed that the Si in the composite films remain in the SiO X (0 < X < 2) state. With the increase of annealing temperature, the higher oxidation state of Si is revealed. A strong and broad PL peak revealed at around 2.24 eV along with the other emissions. The emission could involve a band-to-band recombination mechanism within Si cores and emission sensitive to surface and/or interface states. Evolution of PL emissions and Raman peaks are discussed on the basis of formation of nano-particles and micro-crystals in the films and variation of oxidation state of Si with annealing temperature.
Japanese Journal of Applied Physics, 2012
ZnO nanoparticles were synthesized using sol-gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), Raman spectroscopy, and photoluminescence (PL). XRD analysis demonstrates that the nanoparticles have the hexagonal wurtzite structure and the particle size is increased with annealing temperature. The average size of the nanoparticles was determined by SEM as well as XRD data and found to be 50 nm after annealing at 800 C. A sharp, strong and dominant UV emission with a suppressed green emission has been observed at 300 and 10 K, indicating the good optical properties of ZnO nanoparticles. The 10 K UV band is dominated by a neutral-donor bound exciton, and the surface-related SX emission at 3.31 eV is evidenced. #
Applied Physics Letters, 2005
Abstract Temperature-dependent photoluminescence (PL) of nanocrystalline ZnO thin films grown on Si (100) substrates using a sol–gel method has been investigated. From the PL spectra measured in 83–293 K, the excitonic emissions and their multiple-phonon replicas have been observed in ultraviolet region, and their origins have been identified. Moreover, it has been found that the temperature dependence of the free exciton peak position can be described by standard expression, and the thermal activation energy extracted from the ...
The influence of calcination temperature on optical properties of ZnO nanoparticles
THE 8TH NATIONAL PHYSICS SEMINAR 2019, 2019
ZnO nanoparticles (NPs) have synthesized by sol-gel with different calcination temperatures. Scanning electron microscopy (SEM) shows that the morphology of ZnO NPs has large aggregation. Then, X-ray diffraction (XRD) technique confirmed that the XRD pattern of ZnO NPs has polycrystalline wurtzite structure. The crystallite size in (002) plane at a calcination temperature of 200 o C, 400 o C, 600 o C are 9.28 nm, 12.60 nm, 20.11 nm, respectively. The intensity of observed peaks increases when the calcination temperature is higher. The room temperature UV-Vis absorbance of ZnO NPs indicate that the higher calcination temperature cause absorption peak shifted to longer wavelength and the bandgap energy lower. Optical photoluminescence properties confirmed that the UV emission coincides with the green emissions which correspond to the electron transition from the bottom conduction band to Vo, Vzn, and Ozn level. As a result, all the samples of the ZnO NPs have single broad emission in the range of 330 nm-550 nm with the peak at the UV wavelength of 375 nm. Nevertheless, the PL pattern is not linearly with increasing calcination temperature.
Journal of Luminescence, 2009
The luminescence properties of zinc oxide (ZnO) nanocrystals grown from solution are reported. The ZnO nanocrystals were characterized by scanning electron microscopy, X-ray diffraction, cathodo-and photoluminescence (PL) spectroscopy. The ZnO nanocrystals have the same regular cone form with the average sizes of 100-500 nm. Apart from the near-band-edge emission around 381 nm and a weak yellow-orange band around 560-580 nm at 300 K, the PL spectra of the as-prepared ZnO nanocrystals under high-power laser excitation also showed a strong defect-induced violet emission peak in the range of 400 nm. The violet band intensity exhibits superlinear excitation power dependence while the UV emission intensity is saturated at high excitation laser power. With temperature raising the violet peak redshifts and its intensity increases displaying unconventional negative thermal quenching behavior, whereas intensity of the UV and yellow-orange bands decreases. The origin of the observed emission bands is discussed.
Author's personal copy White-light emission from annealed ZnO:Si nanocomposite thin films
Journal of Luminescence
a b s t r a c t As grown ZnO:Si nanocomposites of different compositional ratios were fabricated by thermal evaporation techniques. These films were subjected to post-deposition annealing under high vacuum at a temperature of 250 1C for 90 min. The photoluminescence (PL) spectra of annealed samples have shown marked improvements both in terms of intensity and broadening. Structural and Raman analyses show formation of a Zn–Si–O shell around ZnO nanoclusters wherein on heating Zn 2 SiO 4 compound forms resulting in huge UV, orange and red peaks at 310, 570 and 640 nm in PL. The new emissions due to Zn 2 SiO 4 completes white light spectrum. The study not only suggests that 1:2 ratio is the best suited for material manipulation but also shows process at the interface of ZnO nanoclusters and silicon matrix leads to new PL emissions. & 2012 Elsevier B.V. All rights reserved.