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Photoluminescence of Squaraine Thin Films: Spatial Homogeneity and Temperature Dependence
Author(s) -
Freese Stefanie,
Lässing Pamina,
Jakob René,
Schulz Matthias,
Lützen Arne,
Schiek Manuela,
Nilius Niklas
Publication year - 2019
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201800450
Subject(s) - photoluminescence , monoclinic crystal system , crystallite , orthorhombic crystal system , thin film , materials science , homogeneity (statistics) , spectroscopy , acceptor , analytical chemistry (journal) , spectral line , crystallography , chemistry , optoelectronics , crystal structure , nanotechnology , condensed matter physics , organic chemistry , statistics , mathematics , physics , quantum mechanics , astronomy , metallurgy
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 μm resolution give insight into the homogeneity of the SQIB films. The high‐temperature films are made of uniform J‐type crystallites of 50–100 μm 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.