A highly luminescent zero-dimensional hybrid tin(II) bromide for white-light emission

Lead-free zero-dimensional (0D) Sn(II) halides are promising broadband emitters, but achieving high efficiency while retaining practical device performance remains challenging. Here, we report [PPAA]₂[SnBr₆]Br₂, comprising triprotonated 3-(piperazin-1-yl)aniline ([PPAA]³⁺) cations, discrete distorted Sn-Br coordination environments, and two noncoordinating charge-balancing bromide ions. Analysis of the six nearest Br neighbors gives a bond-length distortion index of 8.43 × 10^-4 and a nearest Sn⋯Sn separation of 9.004 Å. N-H⋯Br contacts connect the organic cations to both Sn-associated and noncoordinating bromides. The crystals emit at 554 nm with a full width at half-maximum of 106 nm and an absolute photoluminescence quantum yield of 80.9%. Combining this yield with the 1.48 μs lifetime gives effective radiative and nonradiative rates of 5.47 × 10⁵ and 1.29 × 10⁵ s^-1, respectively, under a single-population approximation. Temperature-dependent emission gives an apparent thermal-quenching activation energy of 178.8 meV. The spectroscopy is consistent with self-trapped-exciton-like emission, while ground-state calculations support a contribution from the inorganic units. A phosphor-converted white LED gives chromaticity coordinates of (0.33, 0.33) and a color rendering index of 95. These results connect local coordination, hydrogen-bond contacts, and radiative branching in an efficient lead-free yellow phosphor.