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In a recent work, Nguyen et al. used trSMA-STM to probe electron-phonon dynamics within single carbon dots with nanometer resolution on a picosecond timescale. This promising technique opens up novel avenues to understand fluorescence quantum yield variations in carbon-dot ensembles.

Summary We investigate the rubrene triplet sensitization by perovskite thin films based on methylammonium formamidinium lead triiodide (MAFA) of varying thicknesses. The power-law dependence of both the MAFA photoluminescence (PL) intensity and upconverted emission is tracked as a function of the incident power density. Bimolecular triplet-triplet annihilation (TTA) exhibits a unique power-law dependence with a slope change from quadratic-to-linear at the threshold Ith. The underlying MAFA PL power-law dependence dictates the power law of the upconverted PL: (1) below Ith, the slope of the upconverted PL is twice the value of the MAFA PL; (2) above Ith, it follows the same power law as the underlying recombination of mobile electrons and holes in the MAFA films. We find that the Ith shifts to subsolar incident laser powers when increasing the MAFA thickness above 30 nm. For the thickest MAFA film of 380 nm we find an upconversion threshold of Ith = 7.1 mW/cm2.