Synthesis and Characterization of Lightweight Beryllium Chloro Silicate Phosphor

In this chapter, low weight barium-based cholorsilicate Ba5Cl6Si2O6:Eu2+ is prepared through a solid-state reaction. To confirm the structure of the synthesized phosphors, powder photographs were obtained using an x-ray diffractometer. Photoluminescence spectra and FTIR spectra were recorded. Photoluminescence spectra are studied. The emission peak is observed at 407 nm at excitation 275 nm. The intense violet-blue emission is obtained. The broad excitation band and strong emission indicate that Ba5Cl6Si2O6:Eu2+could be a good phosphor candidate for blue LED and white LEDs. Decay curve indicates the phosphor has a long afterglow feature.

Photoconductivity of Thin Films Obtained from a New Type of Polyindole

The optoelectronic properties of a new poly(2-ethyl-3-methylindole) (MPIn) are discussed in this paper. The absorption and photoluminescence spectra were studied. The electronic spectrum of MPIn showed a single absorption maximum at 269 nm that is characteristic of the entire series of polyindoles. The fluorescence spectra show that the emission peaks of the test sample are centered around 520 nm. The photoconductivity of thin film samples of MPIn polyindole was studied by measuring the current-voltage characteristics under ultraviolet radiation with a wavelength of 350 nm. Samples of phototransistors were obtained, where thin films of MPIn polyindole were used as a transport layer, and their characteristics were measured and analyzed. The value of the quantum efficiency and the values of the mobility of charge carriers in thin polyindole films were estimated.

Effects of an External Magnetic Field on the Interband and Intraband Optical Properties of an Asymmetric Biconvex Lens-Shaped Quantum Dot

The theoretical investigation of interband and intraband transitions in an asymmetric biconvex lens-shaped quantum dot are considered in the presence of an external magnetic field. The selection rules for intraband transitions are obtained. The behaviors of linear and nonlinear absorption and photoluminescence spectra are observed for different temperatures and magnetic field strengths. The second and third harmonic generation coefficients as a function of the photon energy are examined both in the absence and presence of an external magnetic field.

STUDY OF THE COMPOSITION OF GaAsBi FILMS OBTAINED BY PULSED LASER

Методом одноосного холодного прессования были изготовлены мишени GaAsBi с содержанием Bi 1 и 22%. Из полученных мишеней впервые было проведено импульсное лазерное напыления тонких пленок GaAsBi на подложках GaAs и Si. Были исследованы состав, спектры комбинационного рассеяния и фотолюминесценции тонких пленок GaAsBi, полученных из мишеней с содержанием Bi 1 и 22%. По данным спектров фотолюминесценции тонких пленок GaAsBi на подложках GaAs определено, максимальное содержание Bi в пленках не превышает 2,7 %. Полученные результаты хорошо коррелируют с результатами энергодисперсионного анализа, состав пленок, полученных из мишеней с содержанием Bi 1 и 22% - GaAs Bi и GaAsBi. Установлено, что фононная мода LO (GaBi). связанная с нарушением упорядоченности при смешении фаз GaAs и GaBi, находиться на частоте 181 см. Для тонкой пленки, полученной на подложке Si наблюдалась мода LO (GaAs), которая менее выражена и смещена на 3 см влево, в то время как запрещенная правилами отбора мода TO (GaAs) имеет более высокую интенсивность и ее смещение составляет около 1 см относительно частоты TO (GaAs) моды тонкой пленки, полученной на подложке GaAs . Uniaxial cold pressing was used to fabricate the GaAsBi targets with the Bi content of 1 and 22 %. From the obtained targets, pulsed laser deposition of GaAsBi thin films on the GaAs and Si substrates was carried out for the first time. We studied the composition, Raman and PL spectra of thin GaAsBi films obtained from targets with 1 and 22 % of Bi. According to the photoluminescence spectra of thin GaAsBi films on GaAs substrates, it was determined that the maximum content of Bi in the films did not exceed 2,7 %. The results obtained well correlate with the results of the energy dispersive analysis, the composition of films obtained from targets with the Bi content of 1 and 22% - GaAs Bi and GaAsBi. It was found that the LO(GaBi) phonon mode of associated with disordering during mixing of GaAs and GaBi phases to be at a frequency of 181 cm. For the thin film obtained on the Si substrate, the mode LO (GaAs) was observed that was less pronounced and shifted by 3 cm to the left, while the mode TO (GaAs), forbidden by the selection rules, had a higher intensity and its shift was of about 1 cm relative to the frequency of the mode TO (GaAs) of the thin film obtained on the GaAs substrate.

Enrichment of Luminescence via Incorporation of Fluxes in La2Zr2O7:Tb3+ Nanophosphors: One Material, Many Possibilities-Latent Fingerprint Visualization, Anti- counterfeiting, Luminescent Flexible Films

Engineering of single material with multidirectional applications is of crucial for improving the productivity, low cost, flexibility and least power consumption, etc. To achieve these requirements, novel design structures and high performance materials are in urgent need. Lanthanide-doped nanophosphors have greatest strengths and ability in order to tuning its applications in various dimensions. However, nanophosphor applications in latent fingerprints visualization, anti-counterfeiting and luminescent gels/films are still in its infancy. This study demonstrated a simple strategy to enhance the luminescence of Tb3+ doped (1-11 mol %) La2Zr2O7 nanophosphors by conjugating the fluxes via simple solution combustion route. The photoluminescence spectra reveal intense peaks at ~ 491, 546, 587 and 622 nm arises from 5D4◊7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions, respectively. The highest emission intensity was achieved in the NH4Cl flux assisted nanophosphor as compared to NaBr and NH4F. The colorimetric images of fingerprints visualized using optimized nanophosphor on forensic related surfaces exhibit level –III ridge details, including sweat pores, width of the ridges, bifurcation angle, successive distance between sweat pores, etc. These results are decisive parameters which clearly supports the statement “no two persons have ever been found to have the same fingerprints”. The anti-counterfeiting security ink was formulated using nanophosphor and designed various patterns by simple screen printing and dip pen technology. The encoded information was decrypted only under ultraviolet 254 nm light. All the designed patterns are not just what it looks/feels like and how it works. As a synergetic contribution of enhanced luminescence of the prepared nanophosphor, the fabricated green-emissive films display excellent flexibility, uniformity and transparency in the normal and ultraviolet 254 nm light illumination. Aforementioned results revealed that prepared NH4Cl flux assisted La2Zr2O7: Tb3+(7 mol %) NPs are considered to be best candidate for multi-dimensional applications.

Photocatalytic Removal of Antibiotics on g-C3N4 Using Amorphous CuO as Cocatalysts

Amorphous CuO is considered as an excellent cocatalyst, owing to its large surface area and superior conductivity compared with its crystalline counterpart. The current work demonstrates a facile method to prepare amorphous CuO, which is grown on the surface of graphitic carbon nitride (g-C3N4) and is then applied for the photocatalytic degradation of tetracycline hydrochloride. The prepared CuO/g-C3N4 composite shows higher photocatalytic activities compared with bare g-C3N4. Efficient charge transfer between g-C3N4 and CuO is confirmed by the photocurrent response spectra and photoluminescence spectra. This work provides a facile approach to prepare low-cost composites for the photocatalytic degradation of antibiotics to safeguard the environment.

Optical and structural properties of the GaAs heterostructures grown using AlGaAs superlattice buffer layer on compliant Si(100) substrates with the preformed porous-Si (por-Si) layer.

360 nm and 700 nm thick GaAs layers were grown by MO MOCVD growth technique directly on compliant Si (100) substrate and on supper-lattice (SL) AlGaAs buffer layer. The XRD study revealed better structural quality for the sample grown on SL / por-Si buffer. AFM study revealed a smoother sample surface with blocks of more regular rectangular shape and larger size as well. Photoluminescence spectra of the samples revealed an energy shift of PL maximum intensity for both samples. Sample grown on SL buffer also showed higher PL intensity corresponding to better crystalline perfection.

Optical Measurements and Theoretical Modelling of Excitons in Double ZnO/ZnMgO Quantum Wells in an Internal Electric Field

In this paper, the photoluminescence spectra of excitons in ZnO/ZnMgO/ZnO double asymmetric quantum wells grown on a–plane Al2O3 substrates with internal electric-field bands structures were studied. In these structures, the electron and the hole in the exciton are spatially separated between neighbouring quantum wells, by a ZnMgO barrier with different thickness. The existence of an internal electric field generates a linear potential and, as a result, lowers the energy of quantum states in the well. For the wide wells, the electrons are spatially separated from the holes and can create indirect exciton. To help the understanding of the photoluminescence spectra, for single particle states the 8 k·p for wurtzite structure is employed. Using these states, the exciton in the self-consistent model with 2D hydrogenic 1s–like wave function is calculated.

Electrospinning preparation of g-C3N4/Nb2O5 nanofibers heterojunction for enhanced photocatalytic degradation of organic pollutants in water

In this study, graphitic carbon nitride (g-C3N4) and niobium pentoxide nanofibers (Nb2O5 NFs) heterojunction was prepared by means of a direct electrospinning approach combined with calcination process. The characterizations confirmed a well-defined morphology of the g-C3N4/Nb2O5 heterojunction in which Nb2O5 NFs were tightly attached onto g-C3N4 nanosheets. Compared to pure g-C3N4 and Nb2O5 NFs, the as-prepared g-C3N4/Nb2O5 heterojunction exhibited remarkably enhanced photocatalytic activity for degradation of rhodamine B and phenol under visible light irradiation. The enhanced catalytic activity was attributed predominantly to the synergistic effect between g-C3N4 sheets and Nb2O5 NFs, which promoted the transferring of carriers and prohibited their recombination, confirmed by the measurement of transient photocurrent responses and photoluminescence spectra. In addition, the active species trapping experiments indicated that superoxide radical anion (·O2–) and hole (h+) were the major active species contributing to the photocatalytic process. With its high efficacy and ease of preparation, g-C3N4/Nb2O5 heterojunction has great potentials for applications in treatment of organic pollutants and conversion of solar energy.