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Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH3NH3GeI3, HC(NH2)2GeI3, and CsGeI3]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH3NH3+ with Cs+ to control the distortion in (CH3NH3)1-xCsxGeI3, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI3 further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods. [ABSTRACT FROM AUTHOR]

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2(GA)Pb2I7 (HA=n‐hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non‐luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above‐band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two‐fold higher PL emission compared with the pristine (HA)2(GA)Pb2I7. [ABSTRACT FROM AUTHOR]

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2(GA)Pb2I7 (HA=n‐hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non‐luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above‐band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two‐fold higher PL emission compared with the pristine (HA)2(GA)Pb2I7. [ABSTRACT FROM AUTHOR]

Layer-structured materials have shown great promise in photocatalytic applications. The criteria for effective design and selection of superior layered photocatalysts according to their crystal structures are extremely important. Herein, a series of layered perovskites MLa2Ti3O10 (M = Ca, Sr, Ba) and K2xCa1−xLa2Ti3O10 (x = 0.05, 0.11, 0.25) were prepared by an ion-exchange approach from K2La2Ti3O10. Their photocatalytic properties were evaluated by the degradation of methyl orange (MO) and phenol and by photocatalytic hydrogen evolution. Their catalytic activities were significantly improved compared to K2La2Ti3O10, in the order Ca ＞ Sr ＞ Ba ＞ K for both organic pollutant degradation and H2 evolution. The optimized composition of K2xCa1−xLa2Ti3O10 with x = 0.11 shows an increase of four times in photocatalytic efficiency in comparison to pristine K2La2Ti3O10. The underlying mechanism of the improved performance is discussed in detail in terms of the packing factor model, which demonstrates that a more open structure with a lower packing factor possesses higher photocatalytic activity in the layered perovskites. [ABSTRACT FROM AUTHOR]

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2(GA)Pb2I7 (HA=n‐hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non‐luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above‐band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two‐fold higher PL emission compared with the pristine (HA)2(GA)Pb2I7. [ABSTRACT FROM AUTHOR]

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2(GA)Pb2I7 (HA=n‐hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non‐luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above‐band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two‐fold higher PL emission compared with the pristine (HA)2(GA)Pb2I7. [ABSTRACT FROM AUTHOR]