No abstract

Photochemical upconversion uses sensitized triplet-triplet annihilation in bimolecular compositions to convert lower energy photons to higher energy photons. For high efficiency under low illumination, usually a high sensitizer concentration is desirable. However, here we show that the upconversion sensitizer can reduce the emitter triplet lifetime by dynamic quenching, with rate constants on the order 106 M-1 s-1, leading to diminishing returns beyond a certain concentration. These results serve as a warning to designers of photochemical upconvertors that higher concentrations of sensitizers are not necessarily beneficial to upconversion performance.

<div>Here we demonstrate an upconversion composition using semiconductor nanocrystal sensitizers that employs molecular triplet states below the singlet oxygen energy. We show that, contrary to the usual expectation, the admission of oxygen enhances the intensity of upconverted light and significantly speeds up the photochemical processes involved. Further, we demonstrate photochemical upconversion from below the silicon band gap in the presence of oxygen.</div>

The exciton dynamics of violanthrone-79 are investigated in solution and in the solid state. In solution, the photoprepared singlet is found to exhibit a strong ground-state bleach and stimulated emission feature, but when sensitized in its triplet state, it exhibits only a narrow and weak ground-state bleach. As supported by density functional theory calculations, this is explained by the triplet state having absorptions in the same region, with a similar oscillator strength, as the ground-state molecule. In solid films, the excited singlet is found to survive for up to 200 ps, giving way to a long-lived transient absorption spectrum with characteristics reminiscent of the triplet in solution. This is interpreted in terms of singlet fission in the solid film.

This paper reports on the execution and results of an interdisciplinary design project using advanced luminescent solar concentrator PV (LSC PV) technologies in new contexts of use such as the built environment, mobility and consumer products. In the past years LSC PV technologies have been rapidly maturing showing increasing efficiencies up to 10% with high expectations regarding further improvements at low costs. In this context in 2019 a summer school of one week took place aiming at optimally combining design features of LSC PV devices and further enhancements of their performance by scientific research. This design-driven project resulted in several interesting new LSC PV applications which are presented in this paper.