有機無機複合鈣鈦礦材料因其出色的光電特性，如高吸收係數、長載流子傳輸距離、能隙可調與簡易製程，已逐漸成為近年發展新型光電與非線性光學元件中極具潛力的材料。多光子吸收 (multiphoton absorption, MPA) 作為重要的非線性光學機制之一，已在許多研究中展現出重要的應用價值；而鈣鈦礦材料普遍展現出高非線性極化率與顯著的多光子吸收能力。已有研究顯示，在不同波段激發下，MAPbX₃ 系列中的 MAPbI₃ 與 MAPbBr₃ 可進行雙光子吸收 (2PA)，而 MAPbCl₃ 則能在 1064 nm 激發條件下發生三光子吸收 (3PA)。此外，其非線性吸收行為對偏振角度亦呈現依賴性，暗示其晶體結構可能存在異向性，這種現象與理論上立方對稱結構所預期的同向性形成對比，進一步揭示出材料內部的微結構或缺陷可能對其光學特性有深遠影響。因此，本研究以 MAPbCl₃ 單晶為材料，以 1064 nm 雷射光進行激發，並觀察其光致發光行為。實驗結果證實 MAPbCl₃ 可在多光子吸收條件下產生明顯放光，且發光行為隨激發位置、偏振角與溫度變化展現出高度多樣性。其中，發現包含藍、綠、紅與近白光等多色發射，而藍色及綠色螢光波峰具窄半高寬特性，其窄波峰特性推測可能來自強雷射功率下產生的粒子數反轉，結合低溫誘導形成之 strain domain ，使其具備上轉換雷射增益的條件。綜合實驗觀察，MAPbCl₃ 展現出優異的非線性光學響應與多樣化的輻射複合特性，不僅有助於深入理解其能帶結構與複合行為，也顯示其作為上轉換雷射與多波段發光元件之潛力，為單一材料實現白光發光元件提供了可能性。

Organic-inorganic hybrid perovskites have emerged as promising materials for next-generation optoelectronic and nonlinear optical devices, owing to their outstanding properties such as high absorption coefficients, long carrier diffusion lengths, tunable bandgaps, and facile solution processing. Multiphoton absorption (MPA), as one of the key nonlinear optical behaviors, has demonstrated significant potential in diverse applications, while perovskites in particular exhibit inherently large nonlinear susceptibility and pronounced multiphoton absorption responses. In this work, MAPbCl₃ single crystals were investigated through nonlinear optical measurements, with a specific focus on their MPA and photoluminescence (PL) behaviors. Under excitation by a 1064 nm laser, MAPbCl₃ exhibited pronounced three-photon absorption, leading to multicolor emission spanning the blue, green, and red spectral regions, and even approaching near-white light emission. The PL characteristics varied with excitation position, polarization angle, and temperature, suggesting multiple radiative recombination pathways. Notably, the blue and green emission peaks exhibited narrow full-width at half maximum (FWHM), which may be attributed to population inversion induced under high laser power in conjunction with strain domains formed at low temperature. Overall, the experimental observations highlight the excellent nonlinear optical responses and diverse recombination mechanisms of MAPbCl₃. These results not only provide deeper insights into its band structure and carrier dynamics but also demonstrate its potential for applications in up-conversion lasers and multiband light-emitting devices, offering a feasible pathway toward white-light emission from a single material.

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