Nanocomposites and nanomaterials

Influence of confinement effects on the photoluminescence spectra and thermoluminescence of a ladder–type
conjugated polymer
Ostapenko N.I.1, Kerita O.A.1, Ostapenko Yu.V.1, Shcherban N.D.2
1 Institute of Physics, National Academy of Sciences of Ukraine, 46 Prospect Nauky, Kyiv, 03028, Ukraine. 
E-mail: nina.ostapenko@gmail.com
2 L.V. Pisarzhevsky Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 pr. Nauky, Kyiv, 03028, Ukraine.

A comparative study of the photoluminescence spectra (5 K) and thermoluminescence (TSL) (5-120) K of nanocomposite, film and solution of a ladder–type conjugated polymer has been carried out. It has been shown that the introduction of the polymer into silica nanopores allows changing the number of polymer chains in the pores in a controlled manner, their interaction and, accordingly, to control the number and depth of charge carrier traps, as well as their energy dispersion. It has been found that the photoluminescence spectrum of the nanocomposite (when the polymer is incorporated into the nanopores of SBA-15 silica with a diameter of 7 nm) is close to the spectrum of a diluted polymer solution in toluene and shifted relative to the spectrum of the polymer film towards shorter wavelengths. This significant blue shift is due to the decrease of the number of polymer chains in the pore and the reduction of the intermolecular interaction between them. The data obtained in the study of TSL confirm this result: the TSL curve of the nanocomposite is shifted relative to the film curve towards low temperatures by 12 K, and its half-width decreases. This result is in agreement with the data obtained in the investigation of the polymer solution. This indicates a decrease in the number of traps for the charge carriers and dispersion of their energy. The half-width of the density function of energy states for charge carriers, being a measure of energy disorder, in the film and nanocomposite has been determined, and a decrease in the energy disorder in the nanocomposite as a result of confinement effect has been established.