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Abstract: Two models (an upper levels coupling model and a lower levels coupling model) of a four-level atom embedded in a double-band photonic crystal are adopted. The effect of spontaneous [...]

Double perovskite nanocrystals (NCs) have attracted much attention owing to their non-toxicity and excellent semiconducting characteristics. Herein, a series of double perovskite Cs4CuxAg2−2xSb2Cl12 NCs (x = 0.60, 0.75, 0.90, and 1.00) have been synthesized and the relationship between the Cu2+ content and their photo-physical properties has been investigated in detail. The temperature-dependent absorption data point out that the Cu2+ content can affect the transition from the indirect to direct band gap, but hardly influence the evolution of the band edge at different temperatures, which almost linearly red shifts with temperature. The transient absorption technique helps us to obtain the absorption coefficient of these double perovskite NCs. The linear and three-order nonlinear absorption coefficients, which are first measured by transient absorption (TA) and Z-scan techniques, apparently decrease with the Cu2+ content. Intensity-dependent TA curves offer their carrier recombination rate constants (involving the mono-molecular (k1), bi-molecular (k2) and Auger recombination (k3) rate constants). Herein, k1 decreases with the Cu2+ content owing to the variance of Cu–Cl bonds in the x–y plane, but k2 and k3 show an opposite trend. The current–voltage test with strong light bias confirms that the monomolecular recombination is dominant in the operation of photo-detectors based on Cs4CuxAg2−2xSb2Cl12 NC films and the light-harvesting ability should be responsible for the photocurrent of the photo-detector. Our results provide a comprehensive insight into the optoelectronic properties of these double perovskite NCs. [ABSTRACT FROM AUTHOR]

Halide perovskites have attracted attention because of their potential in the fields of light-emitting diodes, lasers and detectors. Herein, a series of quasi-2D PBA2(MAPbBr3)n−1PbBr4 perovskite films have been synthesized and the physical behavior behind their optoelectronic properties, which is dependent on the layer number (n), has been discussed in detail. The temperature-dependent photoluminescence (PL) test indicates that the perovskite film with n = 7 has outstanding PL characteristics, owing to its long radiative lifetime at different temperatures. Temperature-dependent amplified spontaneous emission (ASE) has been employed for the first time to scan the ASE threshold of our films, showing that the ASE threshold decreases from 29.91 μJ cm−2 (3D perovskite film) to 19.23 μJ cm−2 (n = 3). The current–voltage test with strong light bias takes the lead in pointing out that the detector based on the 3D perovskite film (n = ∝) exhibits excellent opto-current properties in comparison with other quasi-2D perovskite films. Our results provide a comprehensive insight into the optoelectronic properties of these quasi-2D perovskite films. [ABSTRACT FROM AUTHOR]

Cs2AgBiBr6 double perovskite nanocrystals (NCs) are materials within the halide perovskite family with promising application potential, owing to their nontoxicity and excellent stability. Herein, Cs2AgBiBr6 NCs were synthesized and their photo-physical properties were investigated in detail. The temperature-dependent photoluminescence (PL) test confirms that their PL mechanism is dependent on the competition between the PL originating from carrier recombination in the conduction band and that in the self-trapping states. Their carrier recombination constants (involving the monomolecular, bimolecular, and Auger recombination rate constants) were obtained from transient absorption data and indicated that the monomolecular recombination decreases with the lowering of temperature, while the bimolecular and Auger recombination show opposite trends. The nonlinear optical properties were studied based on the Z-scan technique, with a two-photon absorption cross section of approximately 1906 GM. Our results suggest that Cs2AgBiBr6 NCs can be extensively applied in the field of optoelectronics, and conventional electronic switches will benefit from the excellent carrier dynamics and nonlinear optical properties. [ABSTRACT FROM AUTHOR]