Lattice Dynamics and Thermal Stability of Cubic-Phase CsPbI₃ Quantum Dots

Cubic-phase CsPbI₃ quantum dots (QDs) have been recently synthesized with merits of excellent optoelectronic performance. However, vital properties of cubic CsPbI₃ including lattice dynamics and stability at high temperature remain poorly explored. We fabricate cubic CsPbI₃ QDs and study their lattice dynamic and thermal stability to 700 K. We obtain Raman modes of cubic CsPbI₃ QDs from 300 to 500 K at ultra-low-frequency range down to 15 cm^-1, consistent with first-principles calculations. Above 550 K, the modification of Raman features suggests sample degradation. Consistently, temperature-dependent photoluminescence measurements indicate the absence of other luminescence phases up to 700 K. With increasing temperature, the CsPbI₃ QD photoluminescence peak has a blue shift with exponentially decreasing intensity, showing faster electronic degradation than structural degradation. Our work provides detailed investigation of CsPbI₃ QD lattice dynamics, band gap, and their high-temperature behavior, potentially useful for their emerging optoelectronic applications.