Photoluminescence of Squaraine Thin Films: Spatial Homogeneity and Temperature Dependence
Photoluminescence of Squaraine Thin Films: Spatial Homogeneity and Temperature Dependence
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DOI：
10.1002/pssb.201800450
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发表时间：
2019-03-01
影响因子：
1.6
通讯作者：
Nilius, Niklas
中科院分区：
文献类型：
--
作者：
Freese, Stefanie;Laessing, Pamina;Nilius, Niklas
利用温度相关和空间分辨的光致发光（PL）光谱研究了旋铸方酸薄膜在不同温度下退火后的光学性质。SQIB是一种具有施主-受主-施主构型的方酸衍生物，在低温和高温下分别具有单斜和正交晶体结构。前者的特征在于典型的H-聚集体的光学响应，而后者显示J-型行为。在温度依赖的PL光谱中，这两种多晶型物通过其特定的振动特征来识别。空间分辨的数据与5 μ m的分辨率给洞察SQIB膜的均匀性。高温薄膜由50-100 μ m大小的均匀J型微晶制成，这也见于偏振相关数据。低温膜包括具有H-和J-特征的颗粒的混合物。它们的特定光谱指纹与在全局PL光谱中检测到的整体发射响应一致。研究表明，SQIB薄膜的光学性能可以探测在单个晶粒的水平和系统的修改，通过热处理。
Temperature-dependent and spatially resolved photoluminescence (PL) spectroscopy is employed to probe the optical properties of spin-cast squaraine thin films annealed to different temperatures. SQIB, a squaraine derivative with donor-acceptor-donor configuration, crystallizes in monoclinic and orthorhombic structures at low and high temperatures, respectively. The former is characterized by an optical response typical for H-aggregates, while the latter shows J-type behavior. In temperature-dependent PL spectra, the two polymorphs are identified via their specific vibrational signature. Spatially resolved data taken with 5 mu m resolution give insight into the homogeneity of the SQIB films. The high-temperature films are made of uniform J-type crystallites of 50-100 mu m size, as also seen in polarization-dependent data. The low-temperature films comprise a mixture of grains with H- and J-character. Their specific spectral fingerprints superimpose to the overall emission response detected in the global PL spectra. The study demonstrates that the optical properties of SQIB thin films can be probed at the level of individual grains and systematically modified by thermal treatment.