Study of power limitation of AlGaInN LEDs in pulse regime at high current

LEDs operating under high pulsed current are of a great interest for different applications, in particular, for VLC (LiFi) systems and laser pumping. Current dependences of the efficiency and emission spectra as well as the rise and fall times of high-power blue LEDs were investigated under extremely high pulse current density up to 7 kA/cm2 and pulse duration from 100 ns to 3 μs. Analysis of the pulse behaviour of the LEDs reveals that the main droop in the efficiency and change in spectra occur up to the current densities ~ 1 kA/cm2 and seems to be non-thermal.

Self-Organized PT-Symmetry of Exciton-Polariton Condensate in a Double-Well Potential

We investigate the dynamics and stationary states of a semiconductor exciton–polariton condensate in a double-well potential. We find that upon the population build-up of the polaritons by above-threshold laser pumping, coherence relaxation due to the phase fluctuations in the polaritons drives the system into a stable fixed point corresponding to a self-organized PT-symmetric phase.

Enhancement of Light Amplification of CsPbBr3 Perovskite Quantum Dot Films via Surface Encapsulation by PMMA Polymer

Photonic devices based on perovskite materials are considered promising alternatives for a wide range of these devices in the future because of their broad bandgaps and ability to contribute to light amplification. The current study investigates the possibility of improving the light amplification characteristics of CsPbBr3 perovskite quantum dot (PQD) films using the surface encapsulation technique. To further amplify emission within a perovskite layer, CsPbBr3 PQD films were sandwiched between two transparent layers of poly(methyl methacrylate) (PMMA) to create a highly flexible PMMA/PQD/PMMA waveguide film configuration. The prepared perovskite film, primed with a polymer layer coating, shows a marked improvement in both emission efficiency and amplified spontaneous emission (ASE)/laser threshold compared with bare perovskite films on glass substrates. Additionally, significantly improved photoluminescence (PL) and long decay lifetime were observed. Consequently, under pulse pumping in a picosecond duration, ASE with a reduction in ASE threshold of ~1.2 and 1.4 times the optical pumping threshold was observed for PQDs of films whose upper face was encapsulated and embedded within a cavity comprising two PMMA reflectors, respectively. Moreover, the exposure stability under laser pumping was greatly improved after adding the polymer coating to the top face of the perovskite film. Finally, this process improved the emission and PL in addition to enhancements in exposure stability. These results were ascribed in part to the passivation of defects in the perovskite top surface, accounting for the higher PL intensity, the slower PL relaxation, and for about 14 % of the ASE threshold decrease.

Optimization of the parameters of a laser induced breakdown spectrometer (LIBS) using probabilistic-deterministic design of experiment

A method for optimizing the settings of a LIBS device aimed at achieving the maximum intensity of analytical lines of the analyte of constant composition is considered using probabilistic-deterministic design of experiments (PDDE). A mixture of Cr, Mn, Fe, Co, and Ni oxides homogenized and diluted by fusion with a lead-phosphate mixture is used as an analyte. It is shown that data of mathematical processing of 25 spectra by the PDDE method can be used to develop mathematical models which relate the line intensity with the energy of the laser pumping lamp, the lag time of the first and second Q-switches, the time delay of the exposure onset, and the total exposure time. The use of the geometric mean and mathematical model in the form of the product of the partial dependences leads to a good correlation between the calculated and experimental values of the intensity for all the considered spectral lines. The simulation results presented for 16 analytical lines of Cr, Mn, Co, and Ni illustrate the applicability of the method under consideration. The experimentally achieved maximum intensities of analytical lines in the matrix of lead-phosphate glass differ from those calculated using the obtained models by 7 – 12 %. There is a linear correlation between the experimental and calculated values of the intensity at R2 = 0.99 and an inclination angle close to 45°. The spectra recorded during the experiment can be used for optimization of other parameters, e.g., the signal-to-noise ratio. The simplicity of calculations and relatively small number of tests in the optimization experiment make the PDDE a promising method for optimizing the LIBS parameters.