Stable, Ultralow Threshold Amplified Spontaneous Emission from CsPbBr3 Nanoparticles Exhibiting Trion Gain.

Wet-chemically synthesized cesium lead halide nanoparticles have many attractive properties that make them promising as optical gain media, but generally suffer from poor stability under ambient conditions and an optical gain threshold that is widely believed to be dictated by the need for biexcitons. These conditions make it impractical for such particles to be utilized as gain media given the need to undergo repeated stimulated emission processes at above-threshold pump intensities over long periods of time. We demonstrate that the surface treatment of CsPbBr3 nanoparticles with a mixture of PbBr2, oleic acid, and oleylamine not only raises their fluorescence quantum yield to nearly unity and prolongs their stability in air from days to months, but it also dramatically increases their trion photoluminescence lifetime from ∼0.9 to ∼1.6 ns. Via a combination of time-resolved photoluminescence and transient absorption spectroscopy, we provide evidence for trion gain at sufficiently low pump intensities in which the likelihood of predominantly biexciton-based gain is small. We then show that, in line with theoretical prediction, the amplified spontaneous emission (ASE) threshold of a thin film of surface-treated CsPbBr3 nanoparticles reduces to a record low of ∼1.2 µJ/cm2 with a corresponding average exciton occupancy per nanoparticle of 0.62. The ultralow pump threshold and increased stability allow for stable ASE over millions of laser shots, paving the way for the deployment of these nanoparticles as viable solution-processed optical gain media.

Singlet Fission Reaction of Light-Exposed ß-Carotene Bound to Bovine Serum Albumin. A Novel Mechanism in Protection of Light-Exposed Tissue by Dietary Carotenoids.

We have attempted to investigate the role of carotenoids (Car) in protecting pigment-protein complexes against light-induced degradation. Upon direct photoexcitation of ß-carotene (ß-Car), nanosecond flash photolysis and femtosecond time-resolved spectroscopy detected a substantial population of triplet states for ß-Car aggregates associated with bovine serum albumin (BSA) or dispersed in aqueous phase with 10% tetrahydrofuran (THF), but none were observed for monomeric ß-Car in neat THF. The direct photogeneration of triplet states was on the time scale of <1 ps, indicating that the underlying reaction mechanism was singlet fission (SF). Efficient triplet-triplet annihilation in the time regime from picoseconds to microseconds resulted in a <1 µs triplet lifetime for ß-Car aggregates, in contrast to a 20 µs lifetime for monomeric ß-Car as determined by anthracene-sensitized flash photolysis. The short-lived triplet excitations of ß-Car aggregates associated with BSA or dispersed in aqueous phase were found to be insensitive to the presence of oxygen, which are considered to be important for the protection of both protein and carotenoid against light-induced degradation via reaction with oxidative species.

Enhanced Light Absorption in Porous Particles for Ultra-NIR-Sensitive Biomaterials.

Conducting polymers with the capability of photothermal conversion extend the application of near-infrared light (NIR), satisfying the demands of less toxicity, easy availability, and high flexibility for NIR-sensitive materials. The improvement of light use efficiency is still urgent and challenging. In this work, an ultra-NIR-sensitive biocompatible porous particle composed of a polylactic acid matrix and polypyrrole nanoparticles is prepared via a one-step double-emulsion method. It is revealed that the light absorption of polyprryole is effectively improved within the porous structure. This particle is exploited as a cost-effective sensing material in terms of its conductivity change for preparing paper-based NIR light sensors. Moreover, the microspheres act as a guardian to encapsulate and lock excess nucleic acids which is useful for preventing inflammatory diseases.