Structural and electronic properties of the air-stable Cs₂SnI₆ defect perovskite have been investigated by applying Raman and photoluminescence spectroscopies in a temperature range of 83 to 433 K. Upon increasing the temperature, the internal Sn-I Raman bands weakly shift to lower energy and broaden. Interestingly, vibrations of Cs atoms against the SnI₆ octahedra are only observed above 293 K, activated by the dynamic lattice anharmonicity. Such lattice modes potentially influence charge-carrier mobilities as well as thermal conductivity of the materials. Intriguing emission properties are also observed with very strong (but not uniform) photoluminescence signals that present high-energy shifts on temperature.