This paper describes the dependence of the spectral-luminescent properties of photosensitizers on their concentration. It has been shown that the initial concentration of the injected photosensitizer or probe can impact on the result of fluorescent diagnostics, in particular on laser flash photolysis and fluorimetric analysis results. Differences of optical measurements have been seen using cancer cells obtained from malignant tumors with different diameters (1–3 cm). These results can be used for the development of optical methods for biomedical diagnostics, for example photosensitizer dose selection.
Laser physics (2014) 3, 035601

Multilayer structures based on matrices of CdSe and CdSe/ZnS nanoparticles in polyimide (PI) and poly[2-methoxy- 5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) were prepared and investigated. A comparison of photoluminescence of the various matrices excited by visible and ultraviolet laser radiation was carried out. The main contribution to the photoluminescence was made by the organic semiconductors. Quantum yield of the luminescence of CdSe nanoparticles embedded in organic semiconductor matrix was found to be lower then that of the individual CdSe nanoparticles dispersed onto a glass substrate. This difference was shown to be a result of charge transfer from the nanoparticles to organic molecules. The nanoparticles were responsible for photovoltage in thin layers of the PI/nanoparticles composites. Processing of a surface of electrodes and organic semiconductors by oxygen plasma increased the photovoltaic efficiency.

Solid thin films of CdSe and CdSe/ZnS nanoparticles on different templates have been investigated under influence of power visible laser radiation. Composite structures including organic semiconductors and CdSe and CdSe/ZnS nanoparticles films have been fabricated. Luminescent and electron properties of the structures have been investigated. Luminescence quantum yield of these nanocomposite structures is shown to exceed that of the films of organic dyes by two orders of magnitude for CdSe nanoparticles with ZnS shell. As for quantum dots without the shell their luminescence quantum yield appears to fall drastically in the films and even in the matrices of organic semiconductors compared to the solution. The presence of CdSe films in multi-layer structures of polyimides leads to abrupt increase in their conductivity by several orders of magnitude. The prospects of development of photovoltaic elements and light-emitting devices including the films with high concentration of CdSe and CdSe/ZnS quantum dots are discussed.

The films with low and high concentrations of CdSe/ZnS nanoparticles have been investigated under action of visible and ultra-violet laser radiation in a wide range of power densities and temperatures. Strong shifts of absorption and luminescence spectra without increase in their width have been observed at the transition from the solution to the films of quantum dots. A complex investigation of anti-stokes luminescence of nanoparticles films has shown its thermal mechanism. Luminescence spectra of the films of quantum dots under action of ultra-violet laser radiation allow monitoring the presence of surface-active TOP and TOPO molecules in the films of quantum dots. The absence of surface-active molecules in the films with high concentration of CdSe/ZnS nanoparticles is shown. The modes of the action of power laser radiation on the films of quantum dots have been investigated. The possibility of controlling the thickness of the films by laser ablation has been shown.

Laser-induced luminescence of multilayer structures based on the solids of CdSe and CdSe/ZnS nanocrystals, different organic semiconductors and on the layers of organic semiconductors with embedded nanocrystals has been investigated. Drastic decrease of luminescence quantum yield is observed in the films of CdSe nanocrystals on organic semiconductors compared to those on optical glasses. The luminescence of the nanocrystals in the matrices of organic semiconductors and in multilayer structures is shown to be suppressed. The effects observed are explained by the transfer of photogenerated carriers from the nanocrystals to the molecules of organic semiconductors. The presence of the charge transfer is confirmed by a drastic increase in the conductivity (by 2 - 4 orders of magnitude) and in photo-voltaic effect at the presence of CdSe and CdSe/ZnS nanocrystals in the structures under investigation. The prospects of using the multilayer structures for development new materials for solar cells are discussed.