Defect
investigation in two-dimensional transition-metal dichalcogenides
(TMDs) is required because structural defects significantly affect
the optical and electrical properties of TMD. Raman scattering can
be an essential tool to study the defects in TMD, but defect-related
Raman modes have been rarely studied. Here, we investigated the influence
of sulfur vacancies and oxygen substitution on the optical properties
of WS2 using the laser irradiation technique. The defect-induced
photoluminescence (PL) exhibits distinct features depending on the
type of defects, which shows different changes in the intensities
and peak positions of the excitons, biexcitons, and defect-bound excitons.
Defect-activated Raman modes revealed information about the defects
and demonstrated the origin of the alteration in PL. The defect analysis
of TMDs based on the correlation between PL and Raman scattering provides
a clear understanding of the variations in their optical properties.
In this work, a simple but effective molecular design strategy is developed for the generation of intense blue emission in the solid state including single crystals through the multiple secondary intermolecular interactions such as CF…HC hydrogen bonding. The synthesized novel imidazole‐based excited‐state intramolecular proton transfer (ESIPT) molecule, 2‐(1‐(3,5‐bis(trifluoromethyl)phenyl)‐4,5‐diphenyl‐1H‐imidazol‐2‐yl)phenol (HPI‐CF3), shows significantly enhanced blue fluorescence in single crystal (ΦF = 0.67) compared to faint emission in solution (ΦF < 0.05). It is considered that tight but slipped stacking structure of HPI‐CF3 molecules in the single crystal not only effectively suppresses the nonradiative decay pathways such as twist intramolecular charge transfer but also induces highly allowed transition character. Taking advantage of the crystallization‐induced emission enhancement characteristics and four‐level ESIPT photocycle process of HPI‐CF3, an efficient amplified spontaneous emission at 475 nm with a threshold of 13.1 mJ cm−2 is observed from the single crystal by picosecond laser optical pumping.
We investigated the photophysical interaction between a conjugated polymer (CP) and a plasmonic gold nanoparticle (Au NP) using transient absorption spectroscopy. We prepared a hybrid system containing CP-stabilized Au NPs by reducing a Au precursor directly with a thiol-terminated poly(3-hexylthiophene) surfactant (P3HT-SH), with the unreacted P3HT-SH chains used as an organic matrix. The P3HT attached to the Au NPs plays two critical roles in our hybrid system: it suppresses exciton quenching from the P3HT matrix to Au NPs (the spacer role) and relays hot electrons induced by surface plasmon resonance of Au NPs to P3HT (the bridge role). Thus, singlet excitons are more slowly relaxed in our hybrid system than those in a neat P3HT film. Our findings may provide important information for development of the high-efficiency hybrid optoelectronic devices.
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