Lack of detailed understanding of the growth mechanism of CsPbBr 3 nanocrystals has hindered sophisticated morphological and chemical control of this important emerging optoelectronic material. Here, we have elucidated the growth mechanism by slowing the reaction kinetics. When 1bromohexane is used as an alternative halide source, bromide is slowly released into the reaction mixture, extending the reaction time from ∼3 s to greater than 20 min. This enables us to monitor the phase evolution of products over the course of reaction, revealing that CsBr is the initial species formed, followed by Cs 4 PbBr 6 , and finally CsPbBr 3 . Furthermore, formation of monodisperse CsBr nanocrystals is demonstrated in a bromide-deficient and lead-abundant solution. The CsBr can be transformed only into CsPbBr 3 nanocubes if additional bromide is added. Our results indicate a fundamentally different growth mechanism for CsPbBr 3 in comparison with more established semiconductor nanocrystal systems and reveal the critical role of the chemical availability of bromide for the growth reactions.

One photon up-conversion photoluminescence is an optical phenomenon whereby the thermal energy of a fluorescent material increases the energy of an emitted photon compared with the energy of the photon that was absorbed. When this occurs with near unity efficiency, the emitting material undergoes a net decrease in temperature, so-called optical cooling. Because the up-conversion mechanism is thermally activated, the yield of upconverted photoluminescence is also a reporter of the temperature of the emitter. Taking advantage of this optical signature, cesium lead trihalide nanocrystals are shown to cool during the up-conversion of 532 nm CW laser excitation. Raman thermometric analysis of a substrate on which the nanocrystals were deposited further verifies the decrease in the local environmental temperature by as much as 25 °C during optical pumping. This is the first demonstration of optical cooling driven by colloidal semiconductor nanocrystal up-conversion.

The oxidation state of the Au ions determines whether cation exchange or gold deposition occurs when an Au salt is added to solutions of all-inorganic cesium lead halide perovskite nanocrystals.

Lack of detailed understanding of the growth mechanism of CsPbBr3 nanocrystals has hindered sophisticated morphological and chemical control of this important emerging optoelectronic material. Here, we have elucidated the growth mechanism by slowing the reaction kinetics. When 1-bromohexane is used as an alternative halide source, bromide is slowly released into the reaction mixture, extending the reaction time from ~3 seconds to greater than 20 minutes. This enables us to monitor the phase evolution of products over the course of reaction, revealing that CsBr is the initial species formed, followed by Cs4PbBr6, and finally CsPbBr3. Further, formation of monodisperse CsBr nanocrystals is demonstrated in a bromide-deficient and lead-abundant solution. The CsBr can only be transformed into CsPbBr3 nanocubes if additional bromide is added. Our results indicate a fundamentally different growth mechanism for CsPbBr3 in comparison with more established semiconductor nanocrystal systems and reveal the critical role of the chemical availability of bromide for the growth reactions.<br>

Lack of detailed understanding of the growth mechanism of CsPbBr3 nanocrystals has hindered sophisticated morphological and chemical control of this important emerging optoelectronic material. Here, we have elucidated the growth mechanism by slowing the reaction kinetics. When 1-bromohexane is used as an alternative halide source, bromide is slowly released into the reaction mixture, extending the reaction time from ~3 seconds to greater than 20 minutes. This enables us to monitor the phase evolution of products over the course of reaction, revealing that CsBr is the initial species formed, followed by Cs4PbBr6, and finally CsPbBr3. Further, formation of monodisperse CsBr nanocrystals is demonstrated in a bromide-deficient and lead-abundant solution. The CsBr can only be transformed into CsPbBr3 nanocubes if additional bromide is added. Our results indicate a fundamentally different growth mechanism for CsPbBr3 in comparison with more established semiconductor nanocrystal systems and reveal the critical role of the chemical availability of bromide for the growth reactions.<br>