A new organometallic “cold−slow” route to strongly fluorescing CdTe/CdS (core−shell) colloids and
transparent films is presented. Based on the optical absorption, fluorescence, FTIR, micro-Raman, XPS, and
XRD data collected on these nanostructures before and after thermal annealing, a mechanistic path of the
core−shell formation and thermal break up is proposed and discussed. The processing of the CdTe/CdS
nanostructures starts with 0.5 M tributylphosphine (TBP) stabilized CdS colloid in dichloromethane as a
solvent. This yellow colloidal oil composed of 3−4 nm CdS clusters is reacted with liquid Bis(trimethylsilyl)-telluride (TMS2Te) in the presence of excess insoluble CdCl2 salt. During this reaction, a rapid chalcogen
atom exchange occurs within a few seconds which produces a new CdTe “core”. The expelled sulfide reacts
slowly with the CdCl2 salt to form new CdS clusters after several hours. Furthermore, this “CdS-formation-driven CdCl2 salt dissolution” activates a strong green-yellow fluorescence indicating a possible evolution of
a “core−shell”-like CdTe/CdS structure. Thermal sintering of the subsequently prepared CdTe/CdS films
between 100 and 200 °C completely suppresses the fluorescence and initiates CdTe cluster growth, reflecting
a high thermal sensitivity of the “core−shell” interfaces. By further raising the sintering temperature to 300−400 °C, the TBP ligands are released and, consequently, bare CdS- and CdTe nanocrystals, as well as ternary
nanocrystalline CdTe
x
S1
-
x
phases, start forming. Above 400 °C, the CdTe part of the nanostructures sublimates,
yielding (111)-oriented CdTe films.
Surface-enhanced Raman spectrum of anthranil (2,1-benzisoxazole) in activated silver colloid was recorded
and compared with the conventional Raman spectrum. The experimentally observed Raman bands along
with their corresponding infrared bands were assigned based on the results of density functional theory (DFT)
calculations. The significant changes evidenced between the SER and normal Raman spectra combined with
the theoretical data obtained for Ag−anthranil model systems demonstrated that this molecule is adsorbed on
the colloidal silver particles through the lone pair electrons of the nitrogen atom. The contribution of the
chemical mechanism to the SERS enhancement was proved by the behavior of the electronic absorption
spectrum of the mixture of activated silver colloid and anthranil solution. The orientation of the adsorbed
species with respect to the metal surface was also predicted.
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