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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 freque...

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.

In this work, we performed a comparison study between the kinetic parameters associated to the KCl:Eu2+ crystal, which is excited separately with ultraviolet light and a source of beta particles. To obtain the kinetic parameters easily (peak and trap parameters), the glow curve deconvolution technique was implemented in a novel and friendly spreadsheet, the KCl:Eu2+ crystal was used as an example. Also, was employed a new mathematical equation to realize the glow curve deconvolution (based on Kiti’s original expressions) and was designed a low cost electronic configuration was implemented. In literature it is reported that, regardless of the excitation source, the glow curves of KCl:Eu2+ crystal have a similar shape. However, when the overlapped peaks are analyzed in detail (using their kinetic parameters), only some peaks of both glow curves have the same kinetic parameters. Some peaks appear only when beta particles are used, while other peaks appear only when UV light is used. The similarity between the glow curves, produced with ionizing and non-ionizing radiation, could indicate a common damage mechanism behind both irradiation processes.

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 evolutionary selection is proposed as the actual growth mechanism of supported layered double hydroxide (LDH) frameworks constituted by interconnected sheet-like structures with apparent preferential orientation. This growth mechanism was emulated through an algorithm that accounts for different synthesis conditions. The generated structures were compared with supported ZnAl-LDH frameworks synthesized by hydrothermal route using different precursor concentrations and reaction temperatures. The simulated structures were found to mimic the topology of the synthesized LDH frameworks. Moreover, the proposed model anticipates the effect of the synthesis parameters in the resulting morphological features. Finally, the distinctive characteristics of those structures generated by the evolutionary selection mechanism are proposed.

There is currently an increased interest in demonstrating white light emitting devices that exhibit a higher energy efficiency compared to the ubiquitous incandescent sources and that are at the same time cost-competitive as well as compatible with a mass-production environment. Under the aforementioned stringent constraints, photoluminescent quantum dots can be considered a suitable option to demonstrate said white light emitting constructs. To this end, the present report discusses the synthesis and characterization of nanoparticles of zinc oxide (ZnO) and zinc sulphide (ZnS) that exhibit Stokes shift effects and optical properties of light absorption in the UV range (~340 nm) and luminescent capabilities obtaining peaks centered in 525 nm and 440 nm, respectively. Colloidal mixtures of these nanostructures were made with different volumetric ratio in order to achieve a near white color emission. Photoluminescence studies of the mixtures were carried out and a chromaticity diagram was made to localize and identify a trend in the luminescent variations of the samples within the International Commission on Illumination (CIE) diagram. The experimental results indicate that quantum dots could be a viable alternative for high-efficiency and cost-competitive white light emitting devices.

Silica-coated cadmium telluride quantum dots (CdTe@SiO2) exhibit increased sensitivity to UV illumination within the 300–400 nm range, allowing long and efficient Stokes-shifted emissions with more than 300 nm of separation from the excitation source. In addition, the surface modification of water-soluble CdTe quantum dots promotes a better dispersibility in a non-polar solvent (chloroform), allowing the facile fabrication of a highly luminescent PMMA/CdTe@SiO2 composite with uniformly distributed CdTe@SiO2 clusters suitable for photonic applications.

ZnO thin films were processed by radio frequency magnetron sputtering at room temperature on p-Si/SiO2 substrates under pure argon (Ar:O2 = 100:0 vol.%) and argon–oxygen mixture (Ar:O2 = 99:1 vol.%) gas environment. Morphological, optical and electrical characteristics of the ZnO films are reported, and they show a clear relationship with the gas mixture employed for the sputtering process. Scanning Electron Microscopy revealed the formation of grains of 15.3 and 19.9 nm average sizes and thicknesses of 59 nm and 82 nm for films growth in pure argon and argon–oxygen, respectively. Photoluminescence measurements at room temperature showed the violet emission band (centered at 3 eV) which was only detected in the ZnO film grown under pure argon. From thermally stimulated conductivity measurements two traps with 0.27 and 0.14 eV activation energies were identified for films grown in pure argon and argon–oxygen mixture, respectively. The trap at 0.27 eV is associated with a level located below the conduction band edge and it is supported by the PL band centered at 3 eV. Both types of ZnO films were used as the active channel layer in thin film transistors with thermal SiO2 as gate dielectric. Field effect mobility, threshold voltage and current ratio were improved in the devices with ZnO channel deposited with the argon–oxygen mixture (99% Ar/1% O2 vol.). Threshold voltage decreased from 25 V to 15 V, field effect mobility and current ratio increased from 0.8 to 2.4 cm2/Vs and from 102 to 106, in that order.

Zinc oxide nanorods decorated with gold nanoparticles were deposited on an optical fiber and were used for carbon dioxide gas detection at room temperature. This optical gas sensor is based on the changes in the intensity of transmitted light due to the interaction of gas molecules with zinc oxide surface. Zinc oxide nanorods were prepared by ultrasonic method and were decorated with spheroidal 20 nm gold nanoparticles. Sensing experiments were carried out using two different wavelengths. The sensor can respond to a CO2 atmosphere and recover to its original state once the gas is removed, showing a better response when red light is used. Moreover, it responds almost linearly with concentration until 2000 sccm. The incorporation of gold nanoparticles greatly reduces the sensitivity of the sensor and increases its recovery time. Preliminary results demonstrate that the sensor could also be used to sense vapors of common solvents.

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.

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.

Silver nanoparticles were synthesized in aqueous solution using an ecofriendly, fast, and easy photochemical technique through the use of Albizia lebbeck (L.) Benth seed (ALS) extract and sunlight. The phytochemical screening of ALS extract revealed the presence of reducing carbohydrates, and saponins. Also, infrared spectroscopy analysis of the ALS extract confirms the presence of functional groups, characteristics of these compounds. The experiments were conducted near noon during winter by exposing aqueous mixtures of silver nitrate and ALS extract to sunlight at 25 °C. The nanoparticles were characterized by optical absorption spectroscopy, Fourier-transform infrared spectroscopy, and scanning transmission electron microscopy. The nanoparticle formation was evaluated by following the temporal evolution of the absorbance. This data was analyzed using first-order kinetics, finding good correlation to the experimental data. The nanoparticle micrograph analysis shows narrow size distribution and acceptable polydispersity indices. The sunlight driven synthesis of silver nanoparticles using ALS extract is more effective to produce small spheroidal AgNPs than sodium citrate. In addition, ALS extract inhibits the growth of nanoparticles with different morphologies, even when both reducing agents are incorporated at the same time. The proposed methodology presents a reliable and sustainable way to obtain small-sized silver nanoparticles according to the principles of green chemistry.

A fiber optic sensor coated with a thin film of zinc oxide nanorods has been developed to detect methanol in adulterated tequila. Zinc oxide was synthesized by ultrasonic method and was used as vapor sensing media. The measured intensities of transmitted light in the optical sensor were analyzed at different concentrations of methanol in tequila. The sensor presented good response to tequila-methanol mixtures and the observed differences in response and recovery times allowed and easy and economic detection of methanol in commercial tequila. The developed sensor is a simple and economic device to detect methanol in commercial tequilas or another beverage. Moreover, it can be used as a quality control technique in laboratories to distinguish the adulteration and/or contamination degree with methanol.

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.

In this article, we present the effects of Ag doping and after-growth thermal annealing on the photoluminescence (PL) and thermoluminescence (TL) behaviors of SnO2 nanoparticles. SnO2 nanoparticles of 4-7 nm size range containing different Ag contents were synthesized by hydrothermal process. It has been observed that the after-growth thermal annealing process enhances the crystallite size and stabilizes the TL emissions of SnO2 nanostructures. Incorporated Ag probably occupies the interstitial sites of the SnO2 lattice, affecting drastically their emission behaviors on thermal annealing. Both the TL response and dose-linearity of the SnO2 nanoparticles improve on 1.0% Ag doping, and subsequent thermal annealing. However, a higher Ag content causes the formation of Ag clusters, reducing both the TL and PL responses of the nanoparticles.

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.

We present the synthesis of ultra-fine, quantum confined SnO2 and SnO2:Ag nanoparticles through a low temperature surfactant-less hydrothermal process. It has been observed that while the incorporation of Ag does not affect the morphology of the nanoparticles, it leads to a reduction of particles size, and generates lattice distortion induced strain in the crystal lattice. Incorporated silver ions occupy mainly the interstitial sites of the crystal lattice, probably forming dopant ion clusters, and drastically quench the photoluminescence emission of the host lattice in the visible region.

Silver nanoparticles were synthesized by direct exposure of mixtures of silver nitrate and sodium citrate to sunlight. The reactions were performed near noon, at ~32 °C during winter, varying the precursors ratio. Nanoparticles were characterized by optical absorption spectroscopy, scanning transmission electron microscopy, as well as proton nuclear magnetic resonance spectroscopy. The kinetic of nanoparticles formation was followed by the temporal evolution of absorbance, and analyzed by using Finke-Watzky two-step model, showing good fit to experimental data. A possible reaction mechanism for the formation of silver nanoparticles is proposed based in the experimental results and the kinetic analysis. This mechanism consists of multiple stages, where the formation of complexes between citrate and cationic silver dimers limits the nucleation process and determines the final size and morphology of the nanoparticles. The proposed approach offers a simple, economic and ecological route for the synthesis of silver nanoparticles.

2,4-Dinitrodiphenylamine (I) , 2-nitro-4-(trifluoromethyl)aniline (II) and 4-bromo-2-nitroaniline (III) have been investigated by DFT and experimental FTIR, Raman and UV–Vis spectroscopies. The gas-phase molecular geometries were consistent with similar compounds already reported in the literature. From the vibrational analysis, the main functional groups were identified and their absorption bands were assigned. Some differences were found between the calculated and the experimental UV–Vis spectra. These differences were analyzed and explained in terms of the TD-DFT/B3LYP limitations, which were mainly attributed to charge-transfer (CT) effects. These findings were in agreement with previous works, which reported that TD-DFT/B3LYP calculations diverge from experimental results when the electronic transitions involve CT. Despite this, TD-DFT/B3LYP calculations provided satisfactory results and a detailed description of the electronic transitions involved in the absorption bands of the UV–Vis spectra. In terms of the NLO properties, it was found that compound (I) is a good candidate for NLO applications and deserves further study due to its good β values. However, the β values for compounds (II) and (III) were negatively affected compared to those found on o- nitroaniline.

Hydrothermally grown SnO2 and SnO2:Eu nanoparticles of 4–11 nm size range were analyzed by photoluminescence (PL) and therrmoluminescence (TL) spectroscopy to study the effect of Eu-doping on their emission behaviors. It has been observed that most of the incorporated Eu3+ ions remain at the interstitial sites of SnO2 lattice. High Eu-contents in the nanoparticles generate lattice deformation, formation of Eu3+/Eu0 clusters at interstitial sites, or segregation to their surfaces. Formation of Eu clusters at interstitial sites enhances electronic defect density in the crystal lattice, reorganizes carrier trapping centers, and modifies their activation energies. Room temperature PL emission and beta-irradiated TL dose response of SnO2 nanoparticles enhance significantly when doped with 0.5 and 1.0 mol. % nominal of Eu3+, respectively, opening up their possibilities of applications in bio-imaging and radiation therapy. Possible mechanisms of enhanced PL and TL responses of the samples have been discussed.

Effects of Ag doping on the crystallinity and optical properties of zinc oxide (ZnO) nanoparticles have been studied by x-ray diffraction, diffuse reflectance spectroscopy, micro-Raman, and photoluminescence spectroscopy. It has been observed that while Ag-doping at low concentration improves the optoelectronic properties of ZnO nanostructures, Ag-doping at high concentrations drastically modify the emission behavior and lattice vibrational characteristics of the nanostructures. High Ag content in ZnO nanostructures causes lattice deformation, induces silent vibrational modes in Raman spectra, and reduces excitonic UV emission due to concentration quenching.