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  1. Covalent functionalization of single-walled carbon nanotubes (SWCNTs) is a promising route to enhance the quantum yield of exciton emission and can lead to single-photon emission at room temperature. However, the spectral linewidth of the defect-related E 11 * emission remains rather broad. Here, we systematically investigate the low-temperature exciton emission of individual SWCNTs that have been dispersed with sodium-deoxycholate (DOC) and polyfluorene (PFO-BPy), are grown by laser vaporization (LV) or by CoMoCat techniques and are functionalized with oxygen as well as 3,5-dichlorobenzene groups. The E 11 excitons in oxygen-functionalized SWCNTs remain rather broad with up to 10 meV linewidth while exciton emission from 3,5-dichlorobenzene functionalized SWCNTs is found to be about one order of magnitude narrower. In all cases, wrapping with PFO-BPy provides significantly better protection against pump induced dephasing compared to DOC. To further study the influence of exciton localization on pump-induced dephasing, we have embedded the functionalized SWCNTs into metallo-dielectric antenna cavities to maximize light collection. We show that 0D excitons attributed to the E 11 * emission of 3,5-dichlorobenzene quantum defects of LV-grown SWCNTs can display near resolution-limited linewidths down to 35 μeV. Interestingly, these 0D excitons give rise to a 3-fold suppressed pump-induced exciton dephasing compared to the E 11 excitons in the same SWCNT. These findings provide a foundation to build a unified description of the emergence of novel optical behavior from the interplay of covalently introduced defects, dispersants, and exciton confinement in SWCNTs and might further lead to the realization of indistinguishable photons from carbon nanotubes. 
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  2. Metal–halide perovskites are promising candidates to advance optoelectronic devices but are known to suffer from rapid material degradation. Here we demonstrate that nanoconfinement is an effective strategy for the long-term stabilization of metal–halide perovskite MAPbI 3 crystals against humidity-induced degradation and temperature-induced polymorph transitions. Two-dimensional X-ray diffraction patterns of MAPbI 3 films reveal an unprecedented air-stability of up to 594 days in non-chemically modified, non-passivated MAPbI 3 films deposited on substrates imposing complete 2D confinement on the tens of nanometers length scale. Temperature-dependent X-ray diffraction analysis and optical spectroscopy further reveal the suppression of temperature-dependent phase transitions in nanoconfined MAPbI 3 crystals. Most notably, the high-temperature cubic phase of MAPbI 3 , typically stable at temperatures above 327 K, remains present until a temperature of 170 K when the perovskite crystals are nanoconfined within the 100 nm diameter pores of anodized aluminum oxide templates. Photoluminescence mapping confirms that nanoconfined MAPbI 3 crystals exhibit spatial uniformity on the tens of microns length scale, suggesting that nanoconfinement is an effective strategy for the formation of high-quality, stable MAPbI 3 crystals across large areas. 
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