Structural and optical properties of highly emitting lead-free double perovskites

This thesis introduces lead-free double perovskite compounds with broad-band white light emission and the potential application of various doped and alloyed double perovskites in the illumination field. In addition, the mechanism of highly efficient warm white light emission is also studied. Double perovskites are promising lead-free perovskite materials which alternatively replace the divalent Pb cations in lead-halide perovskite with a combination of a monovalent and trivalent cation. They exhibit excellent stability under moisture, heat and light. In this work, halide double perovskite materials such as Cs2AgInCl6, Cs2NaInCl6, Cs2AgBiCl6, and Cs2NaBiCl6 are firstly successfully synthesized and their potential application in the optoelectronic field is studied. Cs2AgBiCl6 and Cs2NaBiCl6 possess indirect band gaps while Cs2AgInCl6 and Cs2NaInCl6 have direct band gaps but the dipole transitions between the band edge states are parity-forbidden, which leads to relatively large optical band gaps. However, alloyed double perovskite materials Cs2Na1-xAgxIn1-yBiyCl6 show excellent properties for its highly efficient warm white emission which could be used as a single-component white light emitter. Here, transient absorption and photoluminescence are measured for investigating the outstanding emission properties of Cs2Na1-xAgxIn1-yBiyCl6. Furthermore, Sb alloyed Cs2NaInCl6, Cs2InCl5.H2O and Cs3InCl6 are also prepared which exhibit efficient blue, yellow and blue-green emission respectively under UV light. These materials are promising phosphor in lighting applications. The understanding of luminescence mechanism in double perovskite will help the search and the design of more efficient phosphors.