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.

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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.

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