ZnO nanorods decorated with gold nanoparticles of ∼20 nm average size were fabricated by microwave-assisted chemical synthesis. For the surface-attached growth of metal nanoparticles, the ZnO ...nanostructures were first functionalized by sodium citrate and then the metal ions were reduced under microwave heating. While the incorporation of gold nanoparticles at the surface seen to quench both the band edge and visible emissions of the ZnO nanostructures, it enhances the degradation rate of Rhodamine 6G up to 3 folds under UV emission. The mechanisms of citrate functionalization, growth of Au nanoparticles on the surface of the oxide nanostructures, luminescence emission quenching, and enhanced photocatalytic activity of the composite nanostructures have been discussed.
ZnO-ZnS-SiO
2
composites were synthesized by an ultrasound-assisted Stöber method. The incorporation of blue-emitting ZnS on the surface of ZnO particles allowed the fabrication of a composite ...material with tunable emission. SEM pictures revealed star-shaped ZnO structures with a size about of 1 µm in length with multiple spindles. The composition of the materials was confirmed by EDS, FT-IR, and Raman spectroscopies. X-ray diffraction pattern analysis revealed that ZnO and ZnS have hexagonal wurtzite and cubic sphalerite crystal structures, respectively. The estimated band gap values of ZnS, ZnO, as well as the composites were 3.61, 3.13 and 3.21 eV, respectively. The emission spectrum of star-shaped ZnO exhibits a weak excitonic signal and a second intense and broad band centered around 620 nm. Photoluminescence analysis of the composites revealed a very broad emission band covering almost entirely the visible region of the spectrum and whose emission color ranges from orange to blue region of the CIE1931 chromaticity space, as the content of ZnS in the composite increases. Moreover, this tuning of the luminescence allows the generation of white light.
Sm3+/Eu3+ single doped and co-doped zinc-germanate-tellurite glasses were prepared by the glass melting method. Raman and optical spectroscopic properties of Sm3+, Eu3+ and Sm3+/Eu3+ doped ...TeO2-GeO2-ZnO glasses have been characterized through optical absorption and pulsed/steady fluorescence. Excitation and emission spectra measurements indicated that the energy transfer process Sm → Eu is active in the samples. The concentration of europium ions was varied to provide red emission for possible control over the chromaticity tuning in the red-orange region. Upon 344 nm excitation, the color of the global emission can be adjusted from orange of 2038 K to reddish-orange of 1683 K by increasing the Eu3+ content from 1 up to 2% mol, and co-doped with 0.5% mol Sm3+. Reddish-orange color purity very close to 100% is attained when the phosphors are excited at 406 nm. The time shortening of Sm3+ emission decay in the presence of Eu3+ was attributed to a Sm3+ → Eu3+ non-radiative energy transfer process. From fitting the Sm3+ emission decay profile with the Inokuti-Hirayama model, it was inferred that the energy transfer process could be dominated by an electric dipole-dipole interaction.
•Sm3+ and Eu3+ doped germanate-tellurite glass•Tunable luminescence of doped glasses with Sm3+ and Eu3+ by UV selective excitation•Sm3+ and Eu3+ co-doped glass reddish-orange color purity were very close to 100%
Fabrication of white light-emitting nanophosphors with high luminous efficacy is an urgent need for the next-generation lighting industry and display systems. While rare-earth ions have been ...frequently utilized as dopants to fabricate semiconducting and dielectric nanophosphors, the limited abundance of rare-earth elements on our planet demands a search for suitable alternatives. Here, we report the fabrication of ZnS nanoparticles co-doped with Co2+ and Mn2+ transition metal ions which manifest intense near-white light emission under ultraviolet excitation. While the nanophosphors could be fabricated through a simple low-temperature two-step chemical process, both the color and intensity of their emission can be tuned just by varying the molar concentration of the two dopant ions. The variation of the emission color and its intensity in the nanophosphors due to the dopant ion concentration has been explained considering the interband energy transfer from Mn2+ ions to Co2+ ions and creation of deep level defect states in the host nanocrystals. The synthesis process utilized in the present work opens up the possibility of fabricating low-cost, emission-tuned, rare-earth-free nanophosphors for developing high-efficiency light-emitting devices.
A series of the TeO
2
–GeO
2
–ZnO glass system was single and double doped with different Tb
3+
/Eu
3+
ratios. Their luminescent and colorimetric properties were analyzed for possible use as phosphor ...materials in lighting devices. The characterization by X-ray diffraction and Raman spectroscopy verified the glassy nature of the fabricated samples. The luminescent properties of the doped glasses were analyzed by means of steady-state fluorescence and time-resolved spectroscopy. The Tb
3+
excitation bands observed in the codoped samples while monitoring the 700 nm emission of Eu
3+
, as well as the shortening of Tb
3+
lifetime in presence of europium indicated a Tb
3+
→ Eu
3+
energy transfer, which main interaction type is electric dipole–dipole, according to Inokuti–Hirayama model. The Eu
3+
→ Tb
3+
energy transfer also occurs in the samples but with lower efficiency. The CIE1931 chromaticity coordinates, upon different excitation wavelengths, show a multicolor tunning from green to orange-red due to the lanthanide concentration ratio and the Tb
3+
→ Eu
3+
energy transfer process.
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•Convenient room-temperature gas sensing using ZnO nanorods thin films.•Detection of low concentration of methanol vapors using ZnO nanorods films.•Photoluminescence measurements of ...ZnO as an alternative method for gas detection.•Adsorption of various vapors and their role on the optical properties of ZnO.
Zinc oxide (ZnO) nanorod films with thickness of 700 nm were prepared via a chemical bath deposition method using a ZnO seed layer deposited on a silicon substrate by a conventional dip-coating technique. The morphology and structural properties of the obtained ZnO nanorods were characterized by field emission scanning electron microscopy and Raman spectroscopy. Photoluminescence spectroscopy exhibited an intense emission located at 380 nm related to near band edge (NBE) recombination and a yellow emission band at 575 nm attributed to intrinsic defects of ZnO. Changes in intensity of the NBE and yellow emissions were determined through room-temperature photoluminescence measurements of ZnO nanorods films when exposed to vapors of ethanol, methanol and tequila-methanol mixtures respectively. ZnO nanorods based sensors showed rapid response times and moderate recovery times together with good selectivity for methanol and ethanol vapors. For tequila-methanol mixtures samples, the change in photoluminescence intensity of both said emissions of ZnO nanorods presented an opposite behavior in comparison against methanol and ethanol samples. Intensity changes of the NBE emission showed a linear trend depending on the increase in methanol concentration, while the yellow emission intensity presented an exponential trend for concentrations below 50 % of methanol in tequila.
•Thin films of high crystalline quality were obtained by chemical bath deposition.•Polycrystalline thin films obtained using ammonia nitrate as complexing agent.•Galena and Lanarkite phases were ...obtained using polyethyleneimine complexing agent.•The thin films of chemical-bath-deposition lead sulphide present quantum confinement.
This work presents the structural characterisation of PbS nanofilms deposited by the chemical bath deposition technique at 70±2 °C using Polyethyleneimine, Triethanolamine and Ammonium nitrate as complexing agents, which allow a controlled and constant ion by ion reaction in aqueous medium whose chemical bath reactions take place in basic solutions with typical pH values 9–12, distinguishing the complexes obtained by their thermodynamic stability and kinetic stability. The PbS fundamental stretching frequencies were determined by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy gives the relative atomic composition and identification of the most intense photoelectron transitions S2p (164 eV) and Pb4f 7/2 (137.34 eV) for the PbS-Nitrate film, which are associated with the Pb (II) oxidation state. The shift to higher binding energies, Pb4f7/2 (139.01 eV) for PbS-Polyethyleneimine and PbS-Triethanolamine show the presence of PbO2 with oxidation state Pb (IV). X-ray diffraction analysis and Raman spectroscopy reveal that PbS deposited nanofilms had pure cubic galena crystalline phase when ammonium nitrate was used as complexing agent, with the Polyethyleneimine complexing agent, the formation of cubic PbS in cubic phase with monoclinic Lanarkite Pb2(SO4)2 traces were observed. Finally, using Triethanolamine as complexing agent, cubic phase PbS with orthorhombic Anglesite and lead oxide (x∼1.57) traces were found. The surface morphology of the samples was obtained by High Resolution Transmission Electron Microscopy. The thin films show three direct band gaps, around 0.77–0.78 and 0.84–0.88 eV belonged to the mid-trap state caused by –Pb dangling bond and S+2 levels and the band gap energy at 0.91–1.10 eV was attributed to the quantum confinement associated to grain size, which were obtained by transmittance.
In this study, we report the synthesis and characterization of zinc sulfide quantum dots (ZnS QDs) coated with different concentrations of polyvinylpyrrolidone (PVP), as well as their deployment as ...luminescent films on the window side of previously characterized commercial silicon solar cells to quantify their influence on the power conversion efficiency (PCE). The synthesis of the semiconductor nanoparticles was carried out by the reaction of zinc nitrate with sodium sulfide in an aqueous solution at room temperature. XRD measurements indicated a cubic sphalerite phase of the QDs crystal structure, which was not modified by the addition of PVP in the synthesis process. However, the PVP concentration was a key parameter to modulate the size distribution and the luminescent intensity of the QDs, suggesting that an increase in the PVP concentration produced a slight decrease in the QDs size and improved their luminescent properties desired for the photovoltaic applications. The obtained nanoparticles presented great absorption of photons with energies above 3.72 eV and a broad intense blue photoluminescent emission centered at around 450 nm, under excitation of ultraviolet light of 325 nm. The implementation of the synthesized ZnS QDs as spectral response enhancer produced improvements on the performance of solar cells, leading to increases of 0.7%, 1.9%, and 6.1% on the efficiencies of commercial polycrystalline solar cells after the deposition of ZnS QDs synthesized without PVP, with 0.05 mM PVP and with 0.10 mM PVP, respectively.
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•SnSrO3 nanoparticles prepared by the sonochemical method and solid-state reactions.•Study of rare-earth doping effects on the structure and photoluminescent properties.•XRD results ...confirmed the orthorhombic phase of SrSnO3.•Near-white light emission from Sm3+, Tb3+ co-doped SnSrO3 perovskites.
Sm3+, Tb3+ co-doped SrSnO3 perovskites were successfully prepared by the sonochemical method and solid-state reactions. X-ray diffraction showed well-defined peak characteristics of the SrSnO3 orthorhombic phase, while SEM analysis revealed the formation of rod-like structures composed of particles with a mean size of 100 nm. Under the excitation of 325 nm, the photoluminescence spectra exhibited a broad emission band (380–500 nm) related to intrinsic defects and peaks attributed to characteristic electronic transitions of Tb3+ (5D4→7F6, 489 nm, 5D4→7F5, 542 nm) and Sm3+ (4G5/2→6H5/2, 570 nm, 4G5/2→6H7/2, 605 nm) ions. Through co-doping with these rare earths, the emission from perovskite can be tuned. The obtained chromaticity coordinates are (0.33, 0.31) and (0.34, 0.32) for 4Sm2Tb and 4Sm4Tb perovskites, respectively. It indicates the promising application potential of Sm3+, Tb3+ co-doped SrSnO3 as single-phase perovskite for UV excited white light-diodes.
The results presented here refer to the tunability of global emission characteristics of Eu3+, Dy3+ and Eu3+/Dy3+ ions, varying the composition glasses; TeO2-GeO2-X (X = ZnO, MgCl2). Also, the ...influence of exchanging the modifier compound on the global luminescent response of the glasses was analyzed by Raman spectroscopy, excitation and emission spectra, and emission decay profiles. Changes in the Te-O-Te network structure, when MgCl2 substitutes ZnO, were identified from Raman spectrum deconvolution analysis. The energy transfer between Eu3+ and Dy3+ ions, and tunable emission characteristics, were studied under UV excitations that correspond with the emission of InGaN (370–420 nm) based LEDs. The energy transfer process between Eu3+ and Dy3+ ions was studied based on the emission spectra with different excitation wavelengths and time decay curves of the 5D0→7F2 level of Eu3+ at 612 nm. In TGZED and TGMED glasses and upon 351 nm, the time shortening of Dy3+ emission decay in presence of Eu3+ was attributed to an Dy3+→Eu3+ non-radiative energy transfer process. The energy transfer probabilities PD→E and energy transfer efficiency ηD→E were calculated for TGZ and TGM glasses. According to the Inokuti-Hirayama model it might be dominated through an electric dipole-dipole interaction, with efficiency of 5.0% and 1.9% and the obtained γ6 energy transfer parameter values γ6 = 0.082 ± 0.005 and 0.026 ± 0.005 respectively, for TGZED and TGMED glasses. The non-radiative Eu3+→Dy3+ energy transfer was observed too for both glasses TGZED and TGMED, so that transfer of energy is more favored in the oxide vitreous matrix than in the oxide-halide one. The dominated are an electric dipole-dipole interaction with γ6 energy transfer parameter values are 0.072 ± 0.005 (TGZED) and 0.036 ± 0.005 (TGMED), with efficiency 6.9 and 4.1% respectively. In TGM glasses is very low efficiency of non-radiative Dy3+→Eu3+ and Eu3+ →Dy3+ energy transfer that TGZ matrix. Neutral white emissions of 4135, 4567 K were observed in the Dy3+ and 3914 and 242 K, Eu3+/Dy3+ doped TGZ glasses excited at 351 and 388 nm, respectively. Similarly, global emissions of Dy3+ single doped were 4028 and 4123 K, but in Eu3+/Dy3+ double doped TGM glasses are neutral white light of 3929 and 3979 K, respectively. Upon 394 nm excitation, the Eu3+ doped TGZ and TGM glasses displayed reddish-orange global emissions of 1979 and 1964 K, respectively. For excitations at 382 and 394 nm the Eu3+/Dy3+ doped TGZ and TGM glasses emit warm white light of 3414 and 3160 K (382 nm excitation) and reddish-orange of 2123 and 2030 K (394 nm excitation), respectively, depending mostly on the Eu3+ and Dy3+ relative excitation intensity.
