準二維鈣鈦礦具有天然量子井結構、強激子效應與優異放光特性，適合應用於發光及雷射元件；然而，溶液製程常伴隨混相與晶域不均勻，進而影響激子複合與光學增益。本研究採用溶劑工程結合空間受限成長法製備純相 (PEA)₂MAPb₂I₇ 準二維鈣鈦礦薄膜，並以光學顯微鏡比較不同 DMF/DMSO 比例下的薄膜形貌。結果顯示，DMF/DMSO = 5:5 的樣品可形成較完整且連續的毫米尺度薄膜區域，因此選用此條件進行後續分析。X 光繞射與掠入射廣角 X 光散射顯示薄膜具有高度取向的層狀晶體結構，吸收與光致發光光譜則呈現以約 2.16 eV 為主的 (PEA)₂MAPb₂I₇ 光學特徵。
變溫光致發光量測顯示，隨溫度降低，主激子放光增強並變窄，同時低能側放光明顯增加。主激子放光的熱淬熄分析得到 206 ± 24 meV 的活化能；低能側放光的 Arrhenius 分析則得到 21.6 ± 0.8 meV，與文獻報導的雙激子束縛能相近，顯示低能側包含雙激子相關放光貢獻。於 77 K 下進行的功率相依與偏振相依量測進一步顯示，裂縫／邊緣區域的低能側放光具有較明顯的功率增強，且經儀器響應修正後仍呈現較高的偏振異向性。結果顯示，裂縫與薄膜邊緣所形成的局部能量地形可能促進激子遷移與局域化，進而增強低能側放光。
在高激發條件下，薄膜邊緣區域出現半高寬約 0.25–0.29 nm 的離散窄模態，並具有約 424 μJ cm⁻² 的雷射閾值。不同有效腔長所對應的模態間距與腔長倒數呈近似線性關係，所得有效群折射率約為 3.10 ± 0.17，支持局部薄膜邊緣形成 Fabry–Pérot 型光學回饋。綜合而言，本研究成功製備具高度取向與良好光學均勻性的純相 (PEA)₂MAPb₂I₇ 薄膜，並揭示局部微結構對雙激子相關低能放光、激子局域化與雷射行為的影響。

Quasi-two-dimensional perovskites possess natural quantum-well structures, strong excitonic effects, and excellent luminescence properties, making them promising materials for light-emitting and laser devices. However, solution processing often leads to mixed phases and nonuniform crystalline domains, which can affect exciton recombination and optical gain. In this study, phase-pure (PEA)₂MAPb₂I₇ quasi-2D perovskite films were prepared using solvent engineering combined with a space-confined growth method. Optical microscopy was used to compare the film morphologies obtained with different DMF/DMSO ratios. The sample prepared with DMF/DMSO = 5:5 formed the most complete and continuous millimeter-scale film regions and was therefore selected for further characterization. X-ray diffraction and grazing-incidence wide-angle X-ray scattering revealed a highly oriented layered crystal structure, while the absorption and photoluminescence spectra showed dominant optical features near 2.16 eV corresponding to (PEA)₂MAPb₂I₇.
Temperature-dependent photoluminescence measurements showed that the main exciton emission became stronger and narrower with decreasing temperature, accompanied by enhanced low-energy-side emission. Thermal-quenching analysis of the main exciton emission yielded an activation energy of 206 ± 24 meV. Arrhenius analysis of the low-energy-side emission yielded an effective energy scale of 21.6 ± 0.8 meV, comparable to the reported biexciton binding energy and suggesting a biexciton-related contribution. Power-dependent and polarization-dependent measurements performed at 77 K further showed stronger power enhancement of the low-energy-side emission in the crack/edge region. After correction for the instrumental response, the low-energy side also retained greater polarization anisotropy near the crack/edge region. These results suggest that a locally modified energy landscape near cracks and film edges promotes exciton migration and localization, thereby enhancing the low-energy-side emission.
Under high excitation, a selected film-edge region exhibited discrete narrow modes with linewidths of approximately 0.25–0.29 nm and an estimated lasing threshold of 424 μJ cm⁻². The mode spacing exhibited an approximately linear dependence on the inverse effective cavity length, yielding an effective group refractive index of 3.10 ± 0.17 and supporting Fabry–Pérot-type optical feedback along the local film edge. Overall, this work demonstrates the successful preparation of highly oriented and optically uniform phase-pure (PEA)₂MAPb₂I₇ films and reveals the influence of local microstructures on biexciton-related low-energy emission, exciton localization, and lasing behavior.

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