Solvatochromic Photoluminescent Effects in All-Inorganic Manganese(II)-Based Perovskites by Highly Selective Solvent-Induced Crystal-to-Crystal Phase Transformations.

The development of lead-free perovskite photoelectric materials has been an extensive focus in the recent years. Herein, a novel one-dimensional (1D) lead-free CsMnCl3 (H2 O)2 single crystal is reported with solvatochromic photoluminescence properties. Interestingly, after contact with N,N-dimethylacetamide (DMAC) or N,N-dimethylformamide (DMF), the crystal structure can transform from 1D CsMnCl3 (H2 O)2 to 0D Cs3 MnCl5 and finally transform into 0D Cs2 MnCl4 (H2 O)2 . The solvent-induced crystal-to-crystal phase transformations are accompanied by loss and regaining of water of crystallization, leading to the change of the coordination number of Mn2+ . Correspondingly, the luminescence changes from red to bright green and finally back to red emission. By fabricating a test-paper containing CsMnCl3 (H2 O)2 , DMAC and DMF can be detected quickly with a response time of less than one minute. These results can expand potential applications for low-dimensional lead-free perovskites.

Thermally stable and highly efficient red-emitting Eu3+-doped Cs3GdGe3O9 phosphors for WLEDs: non-concentration quenching and negative thermal expansion.

Red phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs3Gd1 - xGe3O9:xEu3+ (CGGO:xEu3+) (x = 0.1-1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs3EuGe3O9 (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175-250 °C, >90%) than typical red K2SiF6:Mn4+ and Y2O3:Eu3+ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = -5.06 × 10-5/°C, 25-250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials.