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Phonon-assisted upconversion process is one of the important means to generate upconversion photoluminescence (UCPL), and has important applications in laser refrigeration and other fields. However, until now, the studies on UCPL behavior are still insufficient. Herein, this work synthesizes a series of Mn-doped two-dimensional hybrid metal halide (2D HMH) thin films and investigates their optical properties using various spectral techniques. Raman spectroscopic measurement confirms that Mn-doping is achieved via interstitial doping rather than Pb-substitution. By the measurement of the temperature-dependent PL spectrum, it is found that Mn-doping will weaken the thermal expansion effect of 2D HMHs, but will enhance the electron–phonon coupling strength. More importantly, both two-photon-excited and phonon-assisted UCPL are observed in Mn-doped 2D HMHs, with an extremely large phonon-assisted energy gain (approximately 500 meV). Our experimental results are of significance for designing phonon-assisted UCPL materials and expanding their applications. [ABSTRACT FROM AUTHOR]

Due to the pronounced anisotropic response to circularly polarized light, chiral hybrid organic–inorganic metal halides have been regarded as promising candidates for the application in nonlinear chiroptics, especially for the second‐harmonic generation circular dichroism (SHG‐CD) effect. However, designing novel lead‐free chiral hybrid metal halides with large anisotropy factors and high laser‐induced damage thresholds (LDT) of SHG‐CD remains challenging. Herein, we develop the first chiral hybrid germanium halide, (R/S‐NEA)3Ge2I7⋅H2O (R/S‐NGI), and systematically investigated its linear and nonlinear chiroptical properties. S‐NGI and R‐NGI exhibit large anisotropy factors (gSHG‐CD) of 0.45 and 0.48, respectively, along with a high LDT of 38.46 GW/cm2; these anisotropy factors were the highest values among the reported lead‐free chiral hybrid metal halides. Moreover, the effective second‐order nonlinear optical coefficient of S‐NGI could reach up to 0.86 pm/V, which was 2.9 times higher than that of commercial Y‐cut quartz. Our findings facilitate a new avenue toward lead‐free chiral hybrid metal halides, and their implementation in nonlinear chiroptical applications. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic metal halides have emerged as highly promising materials for a wide range of applications in optoelectronics. Incorporating chiral organic molecules into metal halides enables the extension of their unique optical and electronic properties to chiral optics. By using chiral (R)‐ or (S)‐methylbenzylamine (R‐/S‐MBA) as the organic component, we synthesized chiral hybrid copper halides, (R‐/S‐MBA)2CuCl4, and investigated their optical activity. Thin films of this material showed a record anisotropic g‐factor as high as approximately 0.06. We discuss the origin of the giant optical activity observed in (R‐/S‐MBA)2CuCl4 by theoretical modeling based on density functional theory (DFT) and demonstrate highly efficient second harmonic generation (SHG) in these samples. Our study provides insight into the design of chiral materials by structural engineering, creating a new platform for chiral and nonlinear photonic device applications of the chiral hybrid copper halides. [ABSTRACT FROM AUTHOR]