Ion-doping and compression effects on the emission properties of halide double perovskites: transition from non-luminescence to significant emission enhancement

• HDPs-based perovskites Te 4+ :Cs 2 SnCl 6 and Te 4+ :(NH 4 ) 2 SnCl 6 demonstrate significant pressure-induced emission enhancement (PIEE), with their emission intensities increasing by 15 times at 11.3 GPa and 30 times at 6.12 GPa, respectively. These increases correspond to a 6.3-fold and 18.1-fold enhancement in their relative RPLQY compared to ambient conditions. • Further theoretical and experimental analysis reveal that the observed PIEE is primarily attributed to the enhanced oscillator strength of STEs and an optimal exciton-phonon interaction. • The organic NH 4 + cations enhance the relatively flexible structural nature of Te 4+ :(NH 4 ) 2 SnCl 6 . Their interaction with the [SnCl 6 ] 2− octahedra , which involves distortion and tilting, facilitates the phase transition from cubic to tetragonal. In contrast, the cubic phase in Te 4+ :Cs 2 SnCl 6 remains stable even above 30.0 GPa. Doping is the robust technology to modulate the structure and intrinsic physical properties. By introducing ns 2 -metal ions into the lead-free halide double perovskite A 2 SnCl 6 (A = Cs, NH 4 ), an evidently boosting photoluminescence (PL) was observed compared to their host non-luminescent host materials. However, enhancement of PL intensity through ion doping is quite limited. The high-pressure strategy is further employed to modulate emission properties, based on the correlation of the structure and properties. We demonstrate that both Te 4+ :Cs 2 SnCl 6 and Te 4+ :(NH 4 ) 2 SnCl 6 exhibit remarkable pressure-induced emission enhancement (PIEE), with their emission intensities increasing by 15 times at 11.3 GPa and 30 times at 6.12 GPa, respectively, corresponding to a 6.3-fold and 18.1-fold enhancement in their relative photoluminescence quantum yield (RPLQY) compared to ambient conditions. Further theoretical and experimental analysis reveals that the observed PIEE is primarily due to the enhanced oscillator strength of STEs and an optimal exciton-phonon interaction, both of which can be tuned by high pressure. In addition, the organic NH 4 + cations enhance the relatively flexible structural nature of Te 4+ :(NH 4 ) 2 SnCl 6 . Their interaction with the [SnCl 6 ] 2− octahedra , including distortion and tilting, contributes to the phase transition from cubic to tetragonal, in contrast to the persistent cubic phase observed in Te 4+ :Cs 2 SnCl 6 above 30.0 GPa. Results obtained in this wok provide a platform to clarify the structure–property relationships in ion-doped double perovskites and also to explore their potential optoelectronic applications.