This study investigated the optical and structural properties of the Er3+-doped CsPbI3 nanocrystals (CsPbI3:x%Er) embedded into a borosilicate glass matrix. All these inorganic perovskite NCs were synthesized via the fusion method with a subsequent annealing temperature of 500 °C at different times to control NCs size. Transmission Electron Microscopy images showed nanocrystals within the glass matrix with an interplanar distance of d015 = 0.29 nm and an average size ranging from 3.85 to 6.24 nm. The X-ray diffraction data revealed that the CsPbI3:x%Er NCs can present themselves in cubic, tetragonal, or orthorhombic phases depending on the Er-doping concentration. The photoluminescence spectra of the samples annealed for 1–6 h evidence the structural transformation of CsPbI3 NCs from orthorhombic to cubic crystalline structures. The overlap observed between the optical absorption and photoluminescence spectra provided compelling evidence of an energy transfer process among CsPbI3 NCs phases and the electronic state of the Er3+ ions and the time-resolved photoluminescence monitored at 698 nm revealed the existence of distinct emitting levels due to the coexistence of different CsPbI3 NC crystalline structures. The sample doped with 2 % Er3+ and annealed at 500 °C for 6 h demonstrated improvement in the PL emission of the cubic-CsPbI3 NCs, making it suitable for optical applications.
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