ИСТИНА

Study of nanocomposites based quantum dots (QD) is of great importance for fabrication of novel media for radiation generation and control. Employment of liquid-crystal polymers (LCP) as a matrix for the QD embedding is very promising since they allow formation of ordered QD arrays and high QD concentration. Measurement of QD-LCP nanocomposite photoluminescence (PL) spectra and PL kinetics is the first stage of study of such nanocoposites. To reveal an effect of the matrix on carrier recombination in QDs we employed both CdSe and core/shell CdSe/ZnS QD embedded into smectic BA-6PA and amorphous PMBA-6A polymers with various QD mass fractions (up to 60%). QD diameter was 4.1 nm. PL was excited by picosecond Nd:YAG laser pulses at 532 nm. The PL spectra contain two bands (2.15 and 1.70 eV) corresponding to exciton radiative recombination and radiative recombination in defects (traps) at QD-matrix interface, the latter band intensity increases for CdSe in LCP matrix in comparison with amorphous one and practically disappear in CdSe/ZnS QD nanocomposites. Increase of QD concentration results in PL lifetime decrease for QDs in LCP matrices. Time dependence of the PL signal is well described by sum of two decaying exponents for CdSe QD with decay time of 40-60 and 100-300 ns; the latter one disappears for CdSe/ZnS QDs. Comparison of LCP and amorphous matrix QD nanocomposites evidences faster PL decay and less quantum yield in the latter case. Core/shell QDs exhibit more effective PL and weaker effect of the matrix then CdSe QDs. Employing femtosecond Cr:forsterite laser pulses (1250 nm, 80 fs, 80 MHz) allowed us to detect both second-harmonic (SH) and up-converted signals. Depending on types of QDs and matrices, the latter spectrum are either two-photon excited PL trap spectrum or anti-Stokes PL coincides with one excited at 532 nm. The up-conversion could be considered as an anti-Stokes PL in the QDs excited by the SH. In conclusion, PL, SH and up-conversion measurements of CdSe and CdSe/ZnS QDs embedded in the polymer matrices indicate potential use of the LCP for formation of QD nanocomposites allowing effective light generation. This work was supported by Russian Foundation for Basic Research (grant 18-02-00548), synthesis of QDs and polymer matrices was carried out within the State Program of TIPS RAS