Radiation trapping is a well-known process that results in the lengthening of observed fluorescence lifetimes in laser materials with significant overlap in their emission and absorption spectra. The pinhole method is a measurement technique that allows the intrinsic fluorescence lifetime of an excited state to be determined in a nondestructive manner. A theoretical description of this method is proposed. A model is developed that identifies the lifetime extrapolated to a zero radius pinhole as the intrinsic fluorescence lifetime. The application of this method to bulk materials and thin discs is discussed.

Quadruple cation mixed halide perovskite, GA0.015Cs0.046MA0.152FA0.787Pb­(I0.815Br0.185)3, single crystals were grown for the first time using an inverse temperature crystallization process. Solar cell devices in n-i-p stack configuration using thin films of the same materials showed power conversion efficiency above 20%. Complementary time-resolved spectroscopy confirmed that polycrystalline thin films and single crystals identically composed exhibit similar carrier dynamics in the picosecond range. Cooling of excited carriers and bandgap renormalization occur on the same time scale of 200–300 fs. The radiative recombination coefficient (1.2 × 10–9 cm3/s) is comparable to values reported for a GaAs semiconductor. At low excitation density, a long carrier lifetime of 3.2 μs was recorded possibly due to the passivation of recombination centers. This study clarifies discrepancies about the lifetime of hot carriers, the impact of radiative recombination, and the role of recombination centers on solar cell performance. The quadruple cation perovskites displayed short time dynamics with slow recombination of charge carriers.

No abstract

We report on a Yb(3+)-doped sesquioxide waveguide laser based on a lattice-matched Yb(3+)(3%):(Gd,Lu)(2)O(3) film that has been epitaxially grown on Y(2)O(3) using pulsed laser deposition. Rib-channel waveguides have been structured by reactive ion etching. Laser emission at 976.8 nm was observed under pumping with a Ti(3+):Al(2)O(3) laser at 905 nm. A laser threshold of 17 mW and a slope efficiency of 6.7% have been achieved with respect to input power. For an incident pump power of 200 mW, a maximum output power of 12 mW could be realized.

Articles you may be interested inDetermination of chemically active species in a novel microwave plasma source by laserinduced fluorescence J.A onehertz hypocycloidal pinch plasma pump source for ultraviolet dye lasers AIP Conf.

Abstract:We report the first waveguide laser based on a rare-earth-doped sesquioxide. A 2 µm thick lattice matched Nd(0.5%):(Gd, Lu) 2 O 3 film with a nearly atomically flat surface has been epitaxially grown on a Y 2 O 3 substrate, using pulsed laser deposition. The film has been structured with reactive ion etching and a rib channel waveguide laser has been realized. Laser radiation at 1075 nm and 1079 nm has been observed under 820-nm pumping. The laser possesses a threshold power of about 0.8 mW and a preliminary slope efficiency of 0.5% versus incident pump power. A maximum output power of 1.8 mW has been obtained for 370 mW incident pump power.

Exciton intervalley scattering, annihilation, relaxation dynamics, and diffusive transport in monolayer transition metal dichalcogenides are central to the functionality of devices based on them. Here, these properties in a large-size exfoliated high-quality monolayer MoSe 2 are addressed directly using heterodyned transient grating spectroscopy at room temperature. While the free exciton population is found to be long-lived (≈230 ps), an extremely fast intervalley scattering (≤170 fs) is observed, leading to a negligible valley polarization, consistent with steady state photoluminescence measurements and theoretical calculation. The exciton population decay shows an appreciable contribution from the exciton-exciton annihilation, with an annihilation rate of ≈0.01 cm 2 s −1. The annihilation process also leads to a significant distortion of the transient grating evolution. Taking this distortion into account, consistent exciton diffusion constants D ≈ 1.4 cm 2 s −1 are found by a model simulation in the excitation density range of 10 11-10 12 cm −2. The presented results highlight the importance of correctly considering the many-body annihilation processes to obtain a pronounced understanding of the excitonic properties of monolayer transition metal dichalcogenides.

Reabsorption of spontaneously emitted photons by optically active ions in a laser material can significantly affect the measured emission spectra. A measurement technique to suppress reabsorpion artifacts in fluorescence spectra is reported. A theoretical description of the method as well as experimental results are presented. In combination with another version of the pinhole method for the determination of reabsorption-free fluorescence lifetimes, this technique allows one to suppress the influence of reabsorption artifacts in emission cross sections calculated by the Füchtbauer-Ladenburg equation.