In recent years, all-inorganic perovskite CsPbX₃ (X=Cl, Br, I) nanocrystals (NCs) have attracted extensive attention due to their excellent optoelectronic properties^[1-2], such as high fluorescence quantum yield, narrow half-peak width, adjustable bandgap, high absorption coefficient and high carrier mobility^[3], and have broad application prospects in the fields of light-emitting diodes^[4], liquid crystal displays^[5], photodetectors^[6-7] and lasers^[8].

At present, the preparation methods of all-inorganic perovskite NCs mainly include hot-injection method, ligand-assisted reprecipitation method, room temperature synthesis method, etc. Among them, the hot-injection method is favored by people because the NCs with regular morphology and relatively small size distribution can be obtained by this method. However, studies have found that due to the ionic properties of perovskite NCs^[9], perovskite NCs prepared by various methods have fluorescence instability^[10-11] to a certain extent when they are exposed to humidity and light, and are made into devices, which is the primary problem restricting its industrialization. In recent years, important progress has been made in improving the fluorescence stability of all-inorganic perovskite quantum dots by introducing ligands during hot-injection method. However, for perovskite quantum dot films, which are easier to be applied in practice, the related research is very rare. The environment and the state of the ligand may both have changed after film formation, so related research is particularly important. Refs. [12-14] show that deposition of metal oxides (ZnO, Al₂O₃, etc.) on the surface of NCs with atomic layer deposition technology^[12] can effectively improve their stability, and encapsulation of NCs can improve the stability of NC films and their luminous properties^[15-16]. However, the perovskite quantum dot films need to be further researched.

The polarized luminescent properties of perovskite NCs are another concern besides stability. Since the Protesescu research group synthesized inorganic halide perovskite (CsPbX₃, X=Cl, Br, I) NCs in 2015, Sun et al. have studied the fluorescence polarization characteristics of CsPbX₃ NCs, and their measurement results show that the polarization degree of CsPbBr₃ is 0.08^[17]; Zhong et al. embedded perovskite NCs in polymer composite films, and the degree of polarization can be increased to 0.3 through the controllable mechanical stretching. However, after long-term illumination, the fluorescence luminous intensity has a large degree of attenuation^[18]. Therefore, the construction of perovskite quantum dot films with both high fluorescence stability and high polarization characteristics is still an important issue worth exploring.

Metal wire-grid^[19] with a micro-nano scale structure and good polarization performance is widely used in the field of polarization devices such as optical communication and liquid crystal display. In this paper, it is proposed that the CsPbBr₃ NCs modified by Al₂O₃ can be compounded with metal wire-grids to achieve high stability and high polarization luminescence films. With the assistance of the hot-injection method, CsPbBr₃ NCs colloidal solution was synthesized by the ligand modification of the sample with high fluorescence stability reported in the literature. CsPbBr₃ NCs/metal wire-grid composite films were obtained by self-assembly method, and Al₂O₃ passivation layer was deposited on the surface of the composite films by atomic layer deposition technology. The effect of Al₂O₃ passivation layer on the fluorescence intensity of the composite film was compared and analyzed, and the effect of Al₂O₃ deposition on the polarization characteristics of CsPbBr₃ NCs/metal wire-grid composite film was studied.

Cesium carbonate (Cs₂CO₃, 99.99%), Lead bromide (PbBr₂, 99.99%), Oleic acid (OA, AR), 1-Octadecene (ODE, 90%), and (3-Aminopropyl) triethoxysilane (APTES, 97%) were purchased from Aladdin Reagent Company, ethyl acetate was purchased from Tianjin Fuyu Fine Chemical Co., Ltd., n-hexane was purchased from Beijing Chemical Plant, metal wire-grid was purchased from Jiangyin Yunxiang Photonics Co., Ltd.

Preparation of cesium oleate precursor: weigh 0.407 g (1.25 mmol) Cs₂CO₃, put it into a 50 mL four-necked bottle containing 20 mL ODE and 1.2 mL OA, heat the mixed solution in an N₂ environment with a magnetic stirring heater to 120 °C and keep it for 30 minutes, and then continue to raise the temperature to 150 °C to fully react the reactants until the solution is clear and transparent, then keep the obtained precursor at 100 °C for use.

Synthesis of CsPbBr₃ NCs: weigh 0.069 g PbBr₂, put it into a 50 mL three-necked bottle containing 5 mL ODE, 0.5 mL OA and 0.5 mL APTES, heat the mixed solution to 120 °C with a magnetic stirring heater in the N₂ environment for 30 minutes, then continue to raise the temperature to 170 °C, quickly inject 0.4 mL of cesium oleate precursor, react for 1 min, and quickly cool it to room temperature in an ice-water bath. After final cleaning and purification, dissolve in n-hexane for storage.

Configure a certain concentration of CsPbBr₃ NC solution, use the metal wire-grid as the substrate, and lift the mechanical arm of the Langmuir-Blodgett system through the vertical lifting method, so that the CsPbBr₃ NCs and the metal wire-grid are recombined, and finally CsPbBr₃ NCs/ metal wire-grid composite film is obtained.

The Al₂O₃ passivation layer was deposited on the surface of the composite film by atomic layer deposition technology. The process is as follows: with trimethylaluminate as aluminum source and deionized water as oxygen source, the processes of each deposition cycle include water pulse (t₁), N₂ purge (t₂), aluminate pulse (t₃) and N₂ Purge (t₄), the pulse durations are: t₁=0.02 s; t₂=5 s; t₃=0.02 s; t₄=5 s.

The microscopic morphology of NCs particles was characterized by Transmission Electron Microscope (TEM, TecnaiG220S Twin) and Scanning Electron Microscope (SEM, JSM-6010LA), the structural characteristics of the samples are characterized by X-ray diffraction (XRD, D/MAX-Ultima), the absorption spectrum was measured by a UV-Vis spectrophotometer (SHIMADZU, UV-2450), and the fluorescence spectrum was measured by a fluorometer (SHIMADZU, RF-5301pc). In order to investigate the effect of light irradiation on the luminescence properties of CsPbBr₃ NCs/metal wire-grid composite films with or without Al₂O₃ film passivation, a 325nm He-Cd laser was used to irradiate the sample surface for 60 min, respectively, and Raman (Luminescence) spectrometer (labRAM HR E) was used to characterize the photoluminescence characteristics of the sample, and the laser power density on the surface of the sample was 3.15 mW·cm⁻². All tests were done at RT.

The CsPbBr₃ NCs colloidal solution was drop-coated on a silicon wafer to form a thin film, and the results of testing its XRD pattern are shown in Fig. 1 (color online). It can be seen from the Fig. 1. that all the diffraction peaks correspond to the JCPDS standard card (PDF#18-0364), and that the prepared CsPbBr₃ NCs are cubic crystal system. The samples have main diffraction peaks at 2θ of 15.21°, 21.69°, 30.74°, 37.73°, and 43.90°, corresponding to the crystallographic planes (100), (110), (200), (211), and (202) of CsPbBr₃ crystals, respectively, which shows that the crystal has good crystallinity.

Fig. 2(a) shows the results of characterizing the morphology of the obtained CsPbBr₃ NCs by TEM. It can be found that the NCs have a square shape. As shown in Fig. 2(b), the statistics of all particle size distributions. show that the average size of NCs is about 39 nm. Fig. 2(c) shows the SEM image of the CsPbBr₃ NCs film. It can be seen from the Fig. 2(c). that the size of the obtained NCs is relatively uniform and in the shape of a cube, which is basically consistent with the results of TEM. Fig. 2(d) is the SEM image of the CsPbBr₃ NCs film after Al₂O₃ passivation, and it can be found that the Al₂O₃ passivation did not significantly change the surface morphology of the nanofilm.

The absorbance of the CsPbBr₃ NCs solution was measured by a UV-Vis spectrometer, as shown by the dotted line in Fig. 3(a) (color online), which has an obvious absorption peak at 510 nm and a band gap of 2.34 eV. The solid line in Fig. 3(a) is the fluorescence emission spectrum of CsPbBr₃ NCs excited by 365 nm ultraviolet light, the luminescent center is located near 530 nm, and its half-maximum width is only 16.18 nm, indicating that the obtained CsPbBr₃ NCs have excellent luminescent properties. Fig. 3(b) (color online) and Fig. 3(c) (color online) are the physical sample photographs of CsPbBr₃ NCs sol under visible light and the ultraviolet lamp, from which it can be found that the NCs colloid solution of synthesis is yellow-green and an intense green fluorescence is observed under UV lamp irradiation.

In order to take advantage of the excellent optical properties of CsPbBr₃ NCs to realize ultraviolet polarization optical detection, CsPbBr₃ NCs/metal wire-grid composite films were prepared by self-assembly on the metal wire-grid substrate. The solid line in Fig. 4(a) (color online) is the fluorescence emission spectrum of the composite film. It can be found that under the excitation of 325 nm laser, the composite film shows a sharp luminescence peak near 521 nm. Because the surface state has a great influence on the optical properties of perovskite quantum dots, a certain amount of Al₂O₃ is deposited on the surface of the CsPbBr₃/wire-grid composite film by atomic layer deposition method to optimize the optical properties of the composite film. The dotted line in Fig. 4(a) is the fluorescence emission spectrum of the composite film after Al₂O₃ deposition. The comparative analysis reveals that the fluorescence peak intensity of the thin film after coating with Al₂O₃ decreases to 96.47% of the original value, and the luminescence peak position has a red shift of about 1 nm and is accompanied by an increase in the half-peak width, which is due to the fact that the heating of the substrate platform during the atomic layer deposition experiment causes some of the NCs surface ligands to fall off, and the NCs are more likely to produce agglomeration at high temperatures, which enhances the electronic coupling of NCs^[20].

Continuous laser irradiation studies show that the obtained composite films have good fluorescence stability. As shown by the solid line in Fig. 4(b), the fluorescence intensity of the CsPbBr₃ NCs/metal wire-grid composite film remains basically stable within 60 min of continuous irradiation with 325 nm laser (optical power density about 3.15 mW cm⁻²). After Al₂O₃ passivation, the luminous intensity of the composite film can be continuously improved by increasing the irradiation time, and it can be enhanced to about 3.3 times of the initial value at 60 min. As a wide bandgap oxide, Al₂O₃ restricts the migration of photogenerated carriers in perovskite NCs films. Due to the suppression of high energy band gap, the photogenerated carriers and holes are confined inside CsPbBr₃ NCs^[21], so that the luminous intensity of the composite thin film is enhanced after the Al₂O₃ is deposited on the thin film.

In order to verify the changing law of the influence of Al₂O₃ passivation on the fluorescence intensity of CsPbBr₃ NCs thin films, the fluorescence stability of CsPbBr₃ NCs thin films without metal wire-grids was further compared and analyzed. As shown in Fig. 4(c), within 90 min of continuous ultraviolet light irradiation, the fluorescence intensity of the CsPbBr₃ NCs film that has not been passivated by Al₂O₃ has a certain increase in the first 10 min, and then gradually decays to about 1.1 times of the initial fluorescence intensity; while the fluorescence intensity of the CsPbBr₃ NCs film passivated by Al₂O₃ increases with the increase of the irradiation time, and gradually stabilizes at about 2.5 times of the initial fluorescence intensity after about 40 min.

The optical path shown in Fig. 5(a) is used to test the fluorescence polarization characteristics of the obtained CsPbBr₃ NCs/metal wire-grid composite thin film sample. With the linearly polarized ultraviolet light radiated by a He-Cd laser with a wavelength of 325 nm as the excitation light and the periodical adjustment on the polarization direction of the incident linearly polarized light by a UV 1/2λ wave plate with a rotatable spindle, the fluorescence signal of the sample is collected by a monochromator after removing the impact of the excitation light through ultraviolet filter.

Fig. 5(b) shows the fluorescence spectra of the CsPbBr₃ NCs/metal wire-grid composite film without Al₂O₃ passivation treatment under the excitation of ultraviolet light in different polarization directions. In order to clarify the change Law of fluorescence intensity more clearly, Figs. 5(c) 5(d) show the relationship curve of the fluorescence intensity at 521 nm with the polarization direction of incident light for the composite film without Al₂O₃ passivation treatment (5(c)), and with Al₂O₃ passivation treatment (5(d)). It can be found that within a cycle, the fluorescence peak intensities of the CsPbBr₃ NCs/metal wire-grid composite film before and after Al₂O₃ passivation show a cosine-like periodic variation pattern with the change of the polarization angle of the incident light, indicating that the composite film is sensitive to the polarization direction of the incident light, by which can realize the detection of the polarization direction of the incident light. The polarization degree of fluorescence^[22-23] can be determined by the following equation^[24]:

$ P=\frac{{I}_{{\max}}-{I}_{\min}}{{I}_{\max}+{I}_{\min}}\quad, $ ()

where $ {I}_{\max} $ and $ {I}_{\min} $ represent the maximum value and minimum value of the fluorescence luminous intensity of the composite thin film within a cycle of the incident light polarization angle change, respectively. It can be seen from the calculation that the fluorescence polarization of CsPbBr₃ NCs/metal wire-grid composite film is 0.54, while the fluorescence polarization of the composite film after Al₂O₃ surface passivation is 0.36, the above results are higher than the current existing results on the fluorescence polarization of CsPbBr₃ NCs films^[17-18]. In summary, although Al₂O₃ passivation can enhance the fluorescence of composite films, the fluorescence polarization will be decreased after depositing isotropic Al₂O₃ on the surface of anisotropic composite films. The above results can provide reference experience for related follow-up research.

In this paper, cubic phase CsPbBr₃ NCs with good dispersion, uniform particle size distribution and average grain size of about 39 nm are successfully prepared by hot-injection method, and are used to obtain CsPbBr₃ NCs/metal wire-grid composite film by self-assembly technique, and then an Al₂O₃ passivation layer is deposited on the surface of the composite film by the atomic layer deposition technique. Fluorescent stability tests show that the photogenerated carrier confinement effect of the Al₂O₃ passivation layer significantly improves the luminous intensity and stability of the composite film under ultraviolet light. Polarization optical properties tests show that the fluorescence emission intensity of CsPbBr₃ NCs/metal wire-grid composite film is sensitive to the polarization direction of ultraviolet excitation light, and its fluorescence emission intensity changes periodically with the polarization angle of excitation light. The fluorescence polarization of the composite film without Al₂O₃ deposition is 0.54, and the polarization degree reduces to 0.36 after Al₂O₃ deposition. In summary, the deposition of Al₂O₃ passivation layer on the surface of CsPbBr₃ NCs/metal wire-grid composite film by atomic layer deposition technology can improve the stability and fluorescence intensity of the composite film, and the good polarization optical properties that exhibited by the composite film before and after passivation provide a way to prepare ultra-stable perovskite NCs semiconductor device materials with good performance, which have important research significance for the polarization detection of the conversion from ultraviolet to visible light.

近年来，全无机钙钛矿CsPbX₃ (X=Cl, Br, I)纳米晶因其优异的光电性能，包括高的荧光量子产率、窄的半峰宽、可调节的带隙、高的吸收系数以及高载流子迁移速率等^[1-3]而受到广泛关注，在发光二极管^[4]、液晶显示^[5]、光探测器^[6-7]以及激光器^[8]等领域具有广泛的应用前景。

目前，全无机钙钛矿纳米晶的制备方法主要有高温热注入法、配体辅助再沉淀法、室温合成法等，其中高温热注入法因所获得的纳米晶形貌规则，尺寸分布较窄，而受到人们青睐。但研究发现，由于钙钛矿纳米晶的离子特性^[9]，导致在湿度、光照以及制作成器件时，各种方法制备的钙钛矿纳米晶均存在一定程度的荧光不稳定^[10-11]，这是制约其产业化的首要难题。近年来，在提高全无机钙钛矿量子点荧光稳定性方面，人们通过在高温热注入过程中引入配体等手段取得了重要进展。但针对更易于实际应用的钙钛矿量子点薄膜，相关研究还非常少见。而成膜后量子点环境和配体状态可能均发生了改变，因此，相关研究显得尤为重要。文献调研表明，借助原子层沉积技术^[12]在纳米晶的表面沉积金属氧化物^[13-14](ZnO，Al₂O₃等)可有效提高其稳定性，对纳米晶体进行包覆封装，从而提高纳米晶薄膜的稳定性，并对其发光特性进行改善^[15-16]。但针对钙钛矿量子点薄膜的相关研究仍有待探讨。

钙钛矿纳米晶的偏振发光特性是除稳定性外，另一个值得关注的问题。自Protesescu课题组在2015年合成了无机卤化物钙钛矿（CsPbX₃，X=Cl，Br，I）纳米晶后，Sun等人对CsPbX₃纳米晶的荧光偏振特性进行了研究，测得CsPbBr₃的偏振度为0.08^[17]；Zhong等人将钙钛矿纳米晶嵌入聚合物复合薄膜，通过可控的机械拉伸方法，使偏振度提高到0.3，但是经过长时间的光照后，荧光的发光强度有很大程度的衰减^[18]。因此，构建同时具有高荧光稳定性和高偏振特性的钙钛矿量子点薄膜仍然是当前值得探索的重要问题。

金属线栅^[19]具有微纳米尺度结构，偏振性能好，广泛应用于光通讯及液晶显示等偏振器件领域。本文提出借助金属线栅与Al₂O₃修饰的CsPbBr₃纳米晶复合，实现高稳定性和高偏振度发光的薄膜。采用文献报道中可获得高荧光稳定性样品的配体修饰辅助高温热注入法合成了CsPbBr₃纳米晶胶体溶液。通过自组装方法获得CsPbBr₃纳米晶/金属线栅复合薄膜，并以原子层沉积技术在复合薄膜表面沉积了Al₂O₃钝化层。对照分析了Al₂O₃钝化层对复合薄膜的荧光强度的影响，并针对沉积Al₂O₃对CsPbBr₃纳米晶/金属线栅复合薄膜偏振特性的影响进行了研究。

碳酸铯(Cs₂CO₃，99.99%)、溴化铅(PbBr₂, 99.99%)、油酸(Oleic acid, OA, AR)、十八烯(1-Octadecene, ODE, 90%)、(3-氨丙基)三乙氧基硅烷((3-Aminopropyl) triethoxysilane, APTES, 97%)均购自阿拉丁试剂公司，乙酸乙酯购自天津市富宇精细化工有限公司，正己烷购自北京化工厂，金属线栅购自江阴韵翔光电技术有限公司。

油酸铯前驱体的制备：称取0.407 g(1.25 mmol) Cs₂CO₃，将其放入含20 mL ODE和1.2 mL OA的50 mL四颈瓶中，混合溶液在N₂环境中用磁力搅拌加热仪加热到120 °C，并保持30分钟，然后继续升高温度到150 °C，使反应物充分反应至溶液澄清透明后，将得到的前驱体保持在100 °C待用。

CsPbBr₃纳米晶的合成：称取0.069 g PbBr₂，将其放入含有5 mL ODE、0.5 mL OA和0.5 mL APTES的50 mL三颈瓶中，混合溶液在N₂环境中用磁力搅拌均匀，再将加热仪加热到120 °C，持续30分钟，然后继续升高温度到170 °C，迅速注入油酸铯前驱体0.4 mL，反应1 min后快速冰水浴冷却至室温即可，最终清洗提纯后溶于正己烷中保存。

配置一定浓度的CsPbBr₃纳米晶溶液，以金属线栅为衬底，通过垂直提拉法提拉Langmuir-Blodgett拉膜机的机械臂，使得CsPbBr₃纳米晶与金属线栅复合，最终获得CsPbBr₃纳米晶/金属线栅复合薄膜。

使用原子层沉积技术在复合薄膜表面沉积Al₂O₃钝化层。过程如下：以三甲基铝酸盐作为铝源，去离子水作为氧源，每个沉积周期包括水脉冲(t₁)、N₂吹扫(t₂)、铝酸盐脉冲(t₃)和N₂吹扫(t₄)，脉冲持续时间分别为：t₁=0.02 s; t₂=5 s; t₃=0.02 s; t₄=5 s。

使用透射电子显微镜(Transmission Electron Microscope, TEM, TecnaiG220S Twin)和扫描电子显微镜(Scanning Electron Microscope, SEM, JSM-6010LA)表征纳米晶颗粒的微观形貌，使用X射线衍射(X-Ray Diffraction, XRD, D/MAX-Ultima)表征样品的结构特征，采用紫外-可见分光光度计(SHIMADZU, UV-2450)测定吸收光谱，采用荧光分度计(SHIMADZU，RF-5301pc)测定荧光光谱。为了研究光辐照对有无Al₂O₃薄膜钝化的CsPbBr₃纳米晶/金属线栅复合薄膜发光性能的影响，使用325 nm的He-Cd激光器分别对样品表面进行60 min照射，采用拉曼(发光)光谱仪(labRAM HR E)对样品进行光致发光特性的表征，样品表面的激光功率密度为3.15 mW·cm⁻²。所有测试均在室温下完成。

将CsPbBr₃纳米晶胶体溶液滴涂在硅片上形成薄膜，测试其XRD图谱，结果如图1(彩图见期刊电子版)所示。从图中可知，所有衍射峰与JCPDS标准卡(PDF#18-0364)相对应，可知制备的CsPbBr₃纳米晶为立方晶系。样品在2θ分别为15.21°、21.69°、30.74°、37.73°、43.90°处出现主要衍射峰，与CsPbBr₃晶体的(100)、(110)、(200)、(211)、(202)晶面相对应，说明晶体具有良好的结晶性。

利用TEM对所获得的CsPbBr₃纳米晶体形貌进行表征，结果如图2(a)所示。可以发现，纳米晶呈方形形貌。对图中所有粒子尺寸分布进行统计，可知纳米晶的平均尺寸约为39 nm，如图2(b)所示。图2(c)给出了CsPbBr₃纳米晶薄膜的SEM图像。从图中可以看出，所获得的纳米晶尺寸较为均匀，呈立方体形状，与TEM的结果基本一致。图2(d)为Al₂O₃钝化后CsPbBr₃纳米晶薄膜的SEM图像，可以发现Al₂O₃钝化未明显改变纳米薄膜的表面形貌。

通过紫外-可见光分度计测定CsPbBr₃纳米晶溶液的吸光度，如图3(a)(彩图见期刊电子版)中虚线所示，其在510 nm处存在明显的吸收峰，带隙为2.34 eV。图3(a)中实线为CsPbBr₃纳米晶在365 nm紫外光激发下的荧光发射光谱，发光中心位于530 nm附近，且其半高宽度仅为16.18 nm，表明所获得的CsPbBr₃纳米晶具有优异的发光性能。图3(b) (彩图见期刊电子版)和图3(c) (彩图见期刊电子版)是CsPbBr₃纳米晶溶胶在可见光与紫外光下的实物样品照片，从照片中可以看出，合成的纳米晶胶体溶液呈黄绿色，且在紫外灯照射下可观察到强烈的绿色荧光。

为了利用CsPbBr₃纳米晶的优异光学特性实现紫外偏振光学探测，以金属线栅为基底通过自组装方式制备了CsPbBr₃纳米晶/金属线栅复合薄膜。图4(a) (彩图见期刊电子版)中实线为该复合薄膜的荧光发射光谱图。可以发现，在325 nm激光的激发下，复合薄膜在521 nm附近显示出尖锐的发光峰。这是因为表面态对钙钛矿量子点的光学性质有较大的影响，采用原子层沉积方法向CsPbBr₃/金属线栅复合薄膜表面沉积一定量的Al₂O₃，对复合薄膜的光学性质进行优化。图4(a)中虚线为沉积Al₂O₃之后复合薄膜的荧光发射光谱图。对照分析可发现，包覆Al₂O₃后薄膜荧光峰值强度降为原来的96.47%，发光峰位有1 nm左右的红移且伴随半峰宽的增加，这是因为原子层沉积实验过程中，基底平台加热会使部分纳米晶表面配体脱落，高温时纳米晶更容易产生团聚现象，使得纳米晶的电子耦合增强^[20]。

连续激光辐照研究结果表明，所获得的复合薄膜具有良好的荧光稳定性。如图4(b)中实线所示，CsPbBr₃纳米晶/金属线栅复合薄膜在325 nm激光（光功率密度约3.15 mW·cm⁻²）连续辐照60 min内，荧光强度基本保持稳定。而经Al₂O₃钝化后，增加辐照时间可使得复合薄膜的发光强度不断提高，60 min时其可增强为初始值的3.3倍左右。Al₂O₃作为宽禁带氧化物，限制了钙钛矿纳米晶薄膜中的光生载流子迁移，由于高能带隙的抑制作用，光生载流子和空穴被限制在CsPbBr₃纳米晶内部^[21]，使得复合薄膜的发光强度在沉积Al₂O₃薄膜后荧光强度有一定的增强。

为了验证Al₂O₃钝化对CsPbBr₃纳米晶薄膜荧光强度的影响规律，进一步对照分析了未复合金属线栅的CsPbBr₃纳米晶薄膜的荧光稳定性。如图4(c)所示，在紫外光连续照射90 min内，未被Al₂O₃钝化的CsPbBr₃纳米晶薄膜的荧光发光强度在前10 min内有一定的增强，而后逐渐衰减至初始荧光强度的1.1倍左右；而经Al₂O₃钝化后的CsPbBr₃纳米晶薄膜的荧光强度则随着辐照时间的延长而增大，约40 min后逐渐稳定在初始荧光光强的2.5倍左右。

采用如图5(a)所示的光路对所获得的CsPbBr₃纳米晶/金属线栅复合薄膜样品进行荧光偏振特性测试。以波长为325 nm的He-Cd激光器辐射的线偏振紫外光为激发光，以可旋转主轴的紫外1/2λ波片对入射线偏振光的偏振方向进行周期性调节，紫外滤光片去除激发光影响后，样品的荧光信号由单色仪采集。

图5(b)给出了未进行Al₂O₃钝化处理的CsPbBr₃纳米晶/金属线栅复合薄膜在不同偏振方向紫外光激发下的荧光光谱图。为了更清晰地说明荧光强度的变化规律，图5(c)给出了未进行Al₂O₃钝化处理复合薄膜521 nm处荧光强度随入射光偏振方向的变化关系曲线，图5(d)给出了Al₂O₃钝化后复合薄膜在521 nm处荧光强度随入射光偏振方向的变化关系曲线。可以发现，在一个周期内，Al₂O₃钝化前后CsPbBr₃纳米晶/金属光栅复合薄膜荧光峰强度均随入射光偏振角度的改变而呈类余弦的周期性变化规律，说明复合薄膜对入射光的偏振方向敏感，可实现对入射光偏振方向的检测。荧光偏振度^[22-23]可以由以下公式^[24]确定：

$ {P}=\frac{{{I}}_{\text{ma}\text{x}}-{{I}}_{\text{min}}}{{{I}}_{\text{max}}+{{I}}_{\text{min}}}\quad ,$ ()

其中， $ I_{\text{max}} $与 $ {I}_{\text{min}} $分别表示入射光偏振角度在一个周期内变化时，复合薄膜荧光发光强度的最大值与最小值。通过计算可知，CsPbBr₃纳米晶/金属线栅复合薄膜的荧光偏振度为0.54，而经Al₂O₃表面钝化后复合薄膜的荧光偏振度为0.36，以上结果均高于当前关于CsPbBr₃纳米晶薄膜荧光偏振度的已有结果^[17-18]。综上可知，虽然Al₂O₃钝化可实现复合薄膜荧光增强，但在各向异性的复合薄膜表面沉积各向同性的Al₂O₃后，会导致其荧光偏振度降低。以上结果可为后续相关研究提供经验。

本文采用高温热注入法成功制备出分散性良好、粒径分布均匀、平均晶粒约39 nm的立方相CsPbBr₃纳米晶，利用自组装技术获得了CsPbBr₃纳米晶/金属线栅复合薄膜，并通过原子层沉积技术向复合薄膜表面沉积Al₂O₃钝化层。荧光稳定性测试结果表明，Al₂O₃钝化层的光生载流子限制效应使得紫外光照下复合薄膜的发光强度和稳定性有明显提高。偏振光学特性测试表明，CsPbBr₃纳米晶/金属线栅复合薄膜的荧光发射强度对紫外激发光的偏振方向敏感，其荧光发光强度随激发光偏振角度呈周期性变化。未沉积Al₂O₃的复合薄膜荧光偏振度为0.54，沉积Al₂O₃后，各向同性钝化层的引入使得其偏振度降低为0.36。综上所述，通过原子层沉积技术在CsPbBr₃纳米晶/金属线栅复合薄膜表面沉积Al₂O₃钝化层可提高复合薄膜的稳定性和荧光发光强度，钝化前后，复合薄膜均表现出良好的偏振光学特性。本文研究结果为制备性能良好的超稳定钙钛矿纳米晶半导体器件材料提供了一种思路，对实现紫外光波段向可见光波段转化的偏振探测具有重要的研究意义。