Low temperature synthesis of high-quality all-inorganic cesium lead halide perovskite nanocrystals in open air and their upconversion luminescence

- A new thermal process to synthesize monodisperse cubic CsPbX3 nanocrystals.
- Low temperature synthesis in open air.
- More suitable for large-scale synthesizing the CsPbX3 nanocrystals.
- Strong photoluminescence and high quantum yield (∼90%).
- Efficient upconversion photoluminescence in colloidal CsPbX3 nanocrystals.

In this work, a single-step and low-cost synthesis of all-inorganic cesium lead halide perovskite nanocrystals was developed. PbX2 and Cs2CO3 were added to a mixture containing 1-octadecene (ODE), oleic acid (OA) and oleylamine (OLA), and heated at 80-100 °C for 15-30 min in air. The resultant high-quality cube-like CsPbX3 nanocrystals are monodisperse with dimensions of 7-15 nm, and display strong photoluminescence (PL) with a narrow, tuneable emission band of 14-43 nm and a high quantum yield (∼90%). The mechanisms of nucleation and growth were investigated by testing the effects of temperature and surface ligands (OA/OLA) on the crystal morphology and PL intensity. The high quality of the CsPbX3 nanocrystals was further confirmed by efficient upconversion PL with high energy gain, observed here for the first time for colloidal CsPb(Br/I)3 nanocrystals, with an energy gain higher than 430 meV that was mainly attributed to anti-stokes generation rather than the multiphoton effect.