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The crystalline structures of the ternary halides M2BaX4 (M=Cs, Rb; X=Br, Cl), and their luminescence when doped with Eu2+ ions, are reported. These compounds crystallize with the Th3P4 body-centered cubic structure, where the Rb or Cs and Ba cations randomly occupy the Th sites in a 2:1 ratio. The Cs2BaCl4 and Rb2BaCl4 diffraction patterns show a small rhombohedral distortion from this cubic structure, which is accentuated when the compounds are prepared with excess alkali halide. When doped with divalent europium, each compound shows intense photoluminescence with a single emission band centered between 423 and 441 nm. We also find a significant photostimulated luminescence (PSL) effect in all four compounds, with an efficiency of up to 7% relative to the well-known x-ray storage phosphor BaFBr:Eu2+. The PSL effect in Rb2BaBr4 is enhanced by off-stoichiometry preparation or by fluorine doping. Attempts to prepare the related compounds MBa2X5 in single-phase form were unsuccessful. The PSL relative efficiency of a sample containing 34% Rb2BaBr4 and 66% RbBa2Br5 was 1.2% and it increased to 5.3% by doping with 1000 ppm BaF2. [ABSTRACT FROM AUTHOR]

Two pyrazoline core fluorescent materials were designed, synthesized and characterized by various approaches. The synthesized materials were confirmed by standard 1 H NMR and FT-IR techniques. Porous like morphologies were found from SEM analysis and the thermal stability of the materials analyzed with TGA–DSC analysis. Emission properties, quantum yield, lifetime and bandgap energy of the materials have also been studied. Solvent effect of absorption and emission spectral results indicated that the wavelength was red-shifted to increase the solvent polarity. The semiconducting nature was studied by UV–visible spectra, cyclic voltammetry analysis and theoretical calculation. I–V characteristic analysis was used to determine turn-on voltage of the materials for optoelectronics. [ABSTRACT FROM AUTHOR]

The article reports that optoelectronic properties of 2-D and 3-D-grown GaInNAs/GaAs QW light emitting diodes and laser diodes. The optoelectronic properties of light emitting diodes and laser diodes based on GaInNAs/GaAs quantum wells grown under two-dimensional and threedimensional (3-D) conditions are compared. In spite of the longer wavelength, the 2-D LED shows better luminescence properties than the one with island formation. The broadening of the photocurrent spectra and the Stokes shift are used to analyse carrier localisation effects.

The development of the device to measure the lifetime of ZnS luminescent films with different dopants has been presented. The devices have been designed to operate under semi automatic (LMS 01) and program mode (LMS 02) of measuring the parameters of films with setting the input ones. The data are transmitted to a computer and processed by a specialized program that, in its turn, controls the operation of the device, on the whole. [ABSTRACT FROM AUTHOR]

Thermoluminescence of undoped and doped CaB4O7 with activators such as Cu and Mn has been investigated. The polycrystalline samples of undoped and doped CaB4O7 are prepared by melting method. The formation of CaB4O7 compound is checked by X-ray diffraction study and the compound is found to have orthorhombic structure at room temperature. The TSL studies of undoped CaB4O7 sample shows two glow peaks at 150°C and 265%deg;C and one shoulder at around 190°C. The TSL studies of Cu doped CaB4O7 sample also shows two glow peaks at 160%deg;C and 270°C and a shoulder at around 230°C whereas the TSL glow curves of Mn doped CaB4O7 has only one single strong glow peak at 135°C. A comparative TSL studies of these compounds shows that CaB4O7 compound doped with Mn is the most sensitive and the TSL intensity is enhanced by about 40 times when compared with the TSL intensity of undoped CaB4O7 compound. The trap parameters namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the 135°C glow peak of CaB4O7: Mn phosphor are determined using isothermal decay and glow curve shape (Chen's) methods. [ABSTRACT FROM AUTHOR]

To understand both multimodal character of stationary photoluminescence (PL) spectra and observed peculiarities in time-resolved PL in low-dimensional Si structures, it is proposed to take into account an additional effect, which has to emerge in such structures due to indirect-bandgap nature of silicon material. The effect implies that the exciton radiative lifetime becomes a nonmonotonous (oscillating) function of the nanocrystal (NC) size. As a result, in the calculated PL spectra the energy distance between PL peaks or PL minima practically determined by the mean NC size, while dispersion in NC sizes plays a minor role. The qualitative agreement between calculated PL spectra and PL spectra observed experimentally in porous silicon and nanocrystalline silicon (nc-Si) films counts in favor of the used model of radiative exciton recombination. [ABSTRACT FROM AUTHOR]

Optical and electrical properties of green GaP light diode irradiated by gamma irradiation have been studied. Long-lasting relaxation processes on electroluminescence curve of diodes had been observed which one could connect with dark line defects DLD and dark spot defects DSD. Fine structure of negative differential resistance (NDR) region has appeared in I(V)-characteristics at low temperatures (77–110Κ). Gamma ray irradiation leads to the broadening of I(V)-curve where oscillations occur. The same action is observed in I(V)-characteristics treated by ultrasonic. Current oscillations are connected with deep recombination centers in depleted region of GaP light diodes. As these levels are located far enough from p-n junction no one can observe them in TLDS spectra. The much greater voltage oscillation amplitude in the NDR region of I(V)-green diode characteristics comparing with red diodes may be bound with their lower defect level. [ABSTRACT FROM AUTHOR]

In this work, the technique of formation of homogeneous nanoporous silicon layers with high internal surface on solar cell substrates by stain etching is developed. Emission and structure properties of such layers were studied by photoluminescence (PL), photoluminescence excitation, Auger electronic spectroscopy, atomic force microscopy and scanning tunnel microscopy methods. It was observed that nanoporous layers are of high homogeneity and their thickness is ∼20–25 nm. It was shown that the higher PL intensity of such layers in comparison with PL intensity of the layers prepared on standard substrates in the same regimes is connected with the higher internal surface. The increase of PL intensity during prolonged aging in air at the room temperature was observed. [ABSTRACT FROM AUTHOR]

Thermoluminescence of undoped and doped CaB4O7 with activators such as Cu and Mn has been investigated. The polycrystalline samples of undoped and doped CaB4O7 are prepared by melting method. The formation of CaB4O7 compound is checked by X-ray diffraction study and the compound is found to have orthorhombic structure at room temperature. The TSL studies of undoped CaB4O7 sample shows two glow peaks at 150°C and 265%deg;C and one shoulder at around 190°C. The TSL studies of Cu doped CaB4O7 sample also shows two glow peaks at 160%deg;C and 270°C and a shoulder at around 230°C whereas the TSL glow curves of Mn doped CaB4O7 has only one single strong glow peak at 135°C. A comparative TSL studies of these compounds shows that CaB4O7 compound doped with Mn is the most sensitive and the TSL intensity is enhanced by about 40 times when compared with the TSL intensity of undoped CaB4O7 compound. The trap parameters namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the 135°C glow peak of CaB4O7: Mn phosphor are determined using isothermal decay and glow curve shape (Chen's) methods. [ABSTRACT FROM AUTHOR]

OBIC and PL imaging modes of a SOM have been successfully applied to the failure analysis of catastrophically degraded DC-PBH lasers. High lateral resolution, variable in-depth penetration and selective excitation are the most interesting features. A degradation mechanism has been found due to the development of leakage paths in the confining junctions. [ABSTRACT FROM AUTHOR]

A careful analysis of 300 K near-band edge luminescence from bulk CdTe and cadmium telluride films is made. It is shown that: (i) the observed difference in 300 K peak positions of the near-band edge luminescence hvm in CdTe crystals and films, and (ii) the hvm shift to lower energies as the excitation intensity is increased, could not be satisfactory explained by an assumption that free excitons dominate in the formation of the above luminescence. So, the origin of 300 K near-band edge luminescence in CdTe is not mainly the free exciton one as was proposed earlier, and needs further examination. [ABSTRACT FROM AUTHOR]