Impact of cobalt-assisted synthesis on the optical response, surface cobalt and degradation behavior of CsPbBr₃...

All-inorganic CsPbBr₃ quantum dots (QDs) are promising emissive nanomaterials, but their optical response is highly sensitive to local composition, surface passivation, and environmental exposure. Here, pristine CsPbBr₃ and Co-modified CsPbBr₃ QDs were synthesized to examine how cobalt introduction influences nanocrystal structure, photophysics, and analyte-responsive behavior. Electron microscopy and powder X-ray diffraction show that the Co-modified product largely retains the morphology and crystal framework of CsPbBr₃, while inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy show that cobalt is retained in the purified product but resides predominantly at the nanocrystal surface or as a separate cobalt-rich phase, rather than substituting uniformly for Pb in the lattice, with its level tunable through the synthesis feed. Relative to pristine CsPbBr₃, the Co-modified material exhibits altered steady-state and time-resolved photoluminescence, together with a pronounced temperature-dependent emissive response, including formation of a blue-emissive product at lower reaction temperature. Analysis of the quenching kinetics in water, NH₃/H₂O, and N₂H₄/H₂O indicates that the early-stage response is most consistently described by an an empirical 1/I linearization, and that cobalt introduction selectively enhances the quenching response toward ammonia-containing media. These results show that surface-associated cobalt, rather than lattice doping, modulates excited-state relaxation and analyte-dependent optical behavior while preserving the parent perovskite framework, cobalt modifications of the CsPbBr₃ enhancing the analyte-dependent emission response, toward ammonia like species, as a proof-of-concept observation for analyte-responsive perovskite nanocrystals.