Structural, Optical, and Magnetic Properties of Gd Doped CdTe Quantum Dots for Magnetic Imaging Applications

The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.

Effect of Pressure on Electronic and Optical Properties of SrAl2O4

The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.

Investigation of 4,4′- bis [(N carbazole) styryl] biphenyl (BSB4) for a pure blue fluorescent OLED with enhanced efficiency nearing the theoretical limit

4,4′-bis[(N-carbazole) styryl] biphenyl (BSB4 or BSBCz) is one of the widely studied organic fluorescent materials for blue organic electroluminescent devices in the recent times. In this work, BSB4 is used as a guest material to construct the host-guest matrix for the emissive layer (EML) of a pure blue fluorescent organic light-emitting diode (OLED). A pure blue emission suitable for display application with a Commission Internationale de l’Eclairage (CIE) coordinate of (0.147, 0.070) is achieved by the blue-shift of the emission spectrum of the host-guest matrix from that of the pristine guest (BSB4) molecules. The optimization of OLED structures is carried out by considering (i) charge balance in the emissive layer for high exciton density, and (ii) optical interference of generated light in the organic layers for increased light outcoupling. A thorough comparative study on the use of different combinations of widely used hole and electron transport layers to obtain charge balance in the EML of the OLED, thereby enhancing the external quantum efficiency (EQE) is shown. Optical interference effects in the fabricated OLEDs are analyzed by optical simulation of each device structure by transfer matrix method (TMM). With the optimized device structures, we are able to overcome the 2% EQE limit that has been reported so far for blue fluorescent OLEDs with BSB4 as light emitting material and achieve a maximum EQE of 4.08%, which is near to the theoretical limit of EQE for fluorescent OLEDs.

Diluted exciplex concentration in organic light emitting diodes for blue-shifted spectra and improved efficiency

In this work, the effects of different ratios of donor/acceptor and spacer host materials on exciplex organic light emitting diodes (OLED) based DMAC-DPS:PO-T2T were explored, an obvious spectral blue-shift and...

Importance of water and intramolecular interaction governs substantial blue shift of Csp2–H stretching frequency in complexes between chalcogenoaldehydes and water

The considerable blue shift of Csp2–H stretching frequency.

Increasing the photoluminescence intensity of silicon nitride by forming K and N radioactive centres

Creating a light emitter to transfer an electrical signal by optical way has a great importance in development of optoelectronics. The silicon nitride films studied by photoluminescence techniques, and determined luminescence is associated with presence of an extended zone of tail states. Defects play the main role in radiative recombination for structures annealed at 600 °C and 1100 °C. Photoluminescence (Pl) intensity of obtained films by plasma enhanced chemical vapor deposition is increased after annealing at 600 °C which are related to increased concentration of defects as a result of broken Si–H and N–H bonds. Due to the formation of N-centers through the breaking of N–H bonds, annealing at 1100 °C led to sharp decrease in the luminescence intensity 5 and 3 times for SiN1.1 and SiN1.5 samples respectively. Replacement of Si-Si bonds by Si-N enhance Eg with increasing stoichiometric parameter, which leads to blue shift edge of photoluminescence maximum. Carbon implantation of silicon nitride films with extra Si obtained by Plasma Enhanced Chemical Vapor deposition at 1x1014 cm‒2, 2x1015 cm‒2, and 1x1016 cm‒2 fluencies, in combination with prolonged annealing at 1100 °C temperature leads to the formation of additional K-centers.

Colorimetric Monitoring of a Chemical Reaction Using Cesium Lead Halide Assays

Cesium lead halide (CsPbX3, X = F, Cl, Br, I ) nanomaterials have a number of novel optoelectronic and physical properties, both of which are tailorable based on halide type and concentration, such as halide composition-dependent photoluminescence and rapid halide exchange while maintaining crystal structure. In this work we take advantage of these properties and use colloidal CsPbI3 nanoparticles as a proxy and colorimetric sensor of a chemical reaction in real-time. A solvolysis reaction between 2-bromo-2-methylbutane and butanol was used as a model system. A product of reaction, a bromide ion, could be detected via halide exchange with CsPbI3, by way of a quantitative blue shift (Δλ) in photoluminescence. The kinetics of this shift was calibrated against a known Br - source, which allowed for conversion to apparent values solvation kinetics. The observed rate constants (k) and corresponding activation energies (Ea) measured via the CsPbI3 probe were consistent with literature values for the reaction, confirming the validity of the approach.

Dependence of InGaN Quantum Well Thickness on the Nature of Optical Transitions in LEDs

The design of the active region is one of the most crucial problems to address in light emitting devices (LEDs) based on III-nitride, due to the spatial separation of carriers by the built-in polarization. Here, we studied radiative transitions in InGaN-based LEDs with various quantum well (QW) thicknesses—2.6, 6.5, 7.8, 12, and 15 nm. In the case of the thinnest QW, we observed a typical effect of screening of the built-in field manifested with a blue shift of the electroluminescence spectrum at high current densities, whereas the LEDs with 6.5 and 7.8 nm QWs exhibited extremely high blue shift at low current densities accompanied by complex spectrum with multiple optical transitions. On the other hand, LEDs with the thickest QWs showed a stable, single-peak emission throughout the whole current density range. In order to obtain insight into the physical mechanisms behind this complex behavior, we performed self-consistent Schrodinger–Poisson simulations. We show that variation in the emission spectra between the samples is related to changes in the carrier density and differences in the magnitude of screening of the built-in field inside QWs. Moreover, we show that the excited states play a major role in carrier recombination for all QWs, apart from the thinnest one.

Monoelemental two-dimensional iodinene nanosheets: a first-principles study of the electronic and optical properties

Very recently, two-dimensional (2D) iodinene, a novel layered and buckled structure has been successfully fabricated [Mengmeng Qian et al., Adv. Mater. (2020) 2004835]. Motivated by this latest experimental accomplishment, for the first time we conduct density functional theory, firstprinciples calculations to explore the structural, electronic, and optical properties of monolayer, few-layer and bulk iodinene. Unlike the majority of monoelemental 2D lattices, iodinene is predicted to be an intrinsic semiconductor. On the basis of calculations using the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation functional and the Heyd-Scuseria-Ernzerhof (HSE06) functional, it is shown that the electronic bandgap of iodinene decreases with increasing the number of atomic layers. Our HSE06 results reveal that the bandgap of iodinene decreases from 2.08 to 1.28 eV as the number of atomic layers change from one to five, highlighting the finely tunable bandgap. The optical study shows the monolayer has the ability to absorb a wide range of ultraviolet light, more than multilayers and bulk iodinene. As the number of layers increases, the absorption spectra exhibits a blue shift relative to monolayer iodinene. This study confirms the remarkable prospect for the application of iodinene in nanoelectronics and optoelectronics owing to its intrinsic semiconducting nature.