Photophysical properties of halide perovskite CsPb(Br1-xIx)3 thin films and nanowires

This is an accepted manuscript of an article published by Elsevier in Journal of Luminescence on 26/12/2019, available online: https://doi.org/10.1016/j.jlumin.2019.116985 The accepted version of the publication may differ from the final published version.© 2019 Thin films and nanowires based on lead halide perovskites are promising objects for the design of various optoelectronic devices as well as nano- and microlasers. One of the main advantages of such materials is their absorption and photoluminescence spectra tuning across the visible range via the change in their chemical composition, for instance, by substitution of one halide atom (Br) for another one (I) in the crystal lattice of CsPb(Br1-xIx)3. However, this approach gives materials showing unstable photoluminescence behavior caused by light-induced perovskite phase separation under high-intensity excitation at room temperature. In this work, CsPb(Br1-xIx)3 thin films and nanowires are obtained by chemical vapor anion exchange method from their CsPbBr3 counterparts fabricated by improved wet chemical methods. Spontaneous and stimulated emission from the mixed-halide and pristine bromide samples are studied. Tribromide nanowires exhibit lasing with relatively low thresholds (10–100 μJ/cm2) and high Q-factor of the laser mode up to 3500. The temperature dependence of the photoinitiated phase separation in CsPbBr1.5I1.5 samples is investigated, showing that light-induced phase instability of the mixed-halide nanowires can be suppressed at the somewhat higher temperature (250 K) than the value observed for the thin films having a similar chemical composition. The results obtained are important for the optimization of the functioning of optoelectronic devices based on considered perovskite materials.S.V.M. and A.A.Z. thank the Russian Science Foundation (grant 17-73-20336) for the financial support of study of nanostructures. S.V.M. acknowledges funding from the Ministry of Science and Higher Education of the Russian Federation (project 14.Y26.31.0010). M.V. acknowledges funding from the European Regional Development Fund according to the supported activity ‘Research Projects Implemented by World-class Researcher Groups’ under Measure No. 01.2.2-LMT-K-718, grant No. 01.2.2-LMT-K-718-01-0014. G.H. acknowledges ITMO Fellowship Program.Accepted versio

Room temperature operation of AlGaN/GaN quantum well infrared photodetectors at a 3–4 µm wavelength range

Experimental results showing room temperature normal incidence mid-infrared detection by AlGaN/GaN quantum well infrared photodetectors are presented. Designed structures have intersubband transitions corresponding to wavelengths in the region of 3 and 4 µm, where strong absorption in a sapphire substrate dominates. The intersubband spectra, therefore, were characterized by electronic Raman scattering and infrared photocurrent spectroscopy. The absorption spectra agree well with theoretical predictions. Details of device fabrication are presented with sensitivity estimates for the devices

A simple artificial light-harvesting dyad as a model for excess energy dissipation in oxygenic photosynthesis

Under excess illumination, plant photosystem II dissipates excess energy through the quenching of chlorophyll fluorescence, a process known as nonphotochemical quenching. Activation of nonphotochemical quenching has been linked to the conversion of a carotenoid with a conjugation length of nine double bonds (violaxanthin) into an 11-double-bond carotenoid (zeaxanthin). It has been suggested that the increase in the conjugation length turns the carotenoid from a nonquencher into a quencher of chlorophyll singlet excited states, but unequivocal evidence is lacking. Here, we present a transient absorption spectroscopic study on a model system made up of a zinc phthalocyanine (Pc) molecule covalently linked to carotenoids with 9, 10, or 11 conjugated carbon–carbon double bonds. We show that a carotenoid can act as an acceptor of Pc excitation energy, thereby shortening its singlet excited-state lifetime. The conjugation length of the carotenoid is critical to the quenching process. Remarkably, the addition of only one double bond can turn the carotenoid from a nonquencher into a very strong quencher. By studying the solvent polarity dependence of the quenching using target analysis of the time-resolved data, we show that the quenching proceeds through energy transfer from the excited Pc to the optically forbidden S(1) state of the carotenoid, coupled to an intramolecular charge-transfer state. The mechanism for excess energy dissipation in photosystem II is discussed in view of the insights obtained on this simple model system