Results of study of two members of diluted magnetic semiconductor (DMS) family, namely Cd1-xMnxTe and Zn1-xMnxO, which are in form of micro- and nanoparticles generated by pulsed laser ablation in liquid medium (PLAL), have been presented. The structural analysis using X-ray diffraction (XRD) of nanocrystals indicated that Mn has entered the AIIBVI lattice without changing the crystal structure and systematically substituted the A2+ ions in the lattice. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. The scanning electron microscopy (SEM) clearly illustrates flower-like particles of Zn1-xMnxO, which consist of nanosheets and nanoleaves with average thickness about (5-8) nm. Obviously, these nanoobjects are responsible for the observed blue shift of the absorption edge in DMS nanostructures. In magneto-optical Faraday rotation spectra of both Cd1-xMnxTe and Zn1-xMnxO nanostructures there were exhibited peculiarities associated with s,p-d spin exchange interactions and confinement effect. It was observed almost linear dependence of the Faraday rotation as function of magnetic field strength for nanoparticles in contrast to the dependence with saturation in bulk case.
Two-dimensional (2D) materials such as GaSe, InSe, and WSe2 in form of bulk crystal and few-layer sheets have been prepared by mechanical exfoliation method. Atomic force microscopy (AFM) analysis was used for the study of surface morphology and estimation of thicknesses of the exfoliated thin semiconductor layers. Optical absorption and magneto-optical Faraday rotation spectra of 2D materials at different temperatures have been studied. In spectral region near long-wavelength absorption edge for all the studied layered crystals at low temperatures the exciton series have been observed. It was shown that in GaSe and InSe crystals these series consist of three lines, whereas in WSe2 two exciton lines were revealed. The observed exciton series were interpreted in framework of 3D exciton model. In the absorption spectra of GaSe and InSe crystals at higher photon energies than band gap Eg additional exciton structure also was observed. In case of thin exfoliated WSe2 flakes with thickness less than 80 nm shift of ground exciton band to shorter wavelengths has been revealed, which is associated with quantum size effect. Faraday rotation spectra of the 2D crystals have been confirme INTRODd dominant role of excitons near absorption edge.
Nanocrystals of Pb1-xFexI2 with x up to 0.05 embedded in transparent polymer matrix have been studied by optical absorption, photoluminescence and electron paramagneric resonance. The composite nanostructures containing the semimagnetic semiconductor nanocrystals of Pb1-xFexI2 have been prepared by cooling to the room temperature of boiling saturated aqueous solution. The absorption spectra of nanoparticles exhibit blue shift due to quantum confinement effect. For colloidal solution of nanocrystals and nanostructures incorporated in polymer matrix based on polyvinylalcohol exciton structures of absorption spectra was observed. In photoluminescence spectra of nanoparticles two main peaks were revealed, which are attributed to the band-edge transmission and defects states. The substitutional incorporation of iron ions at lead sites is reflected in EPR studies. Isolated as well as interacting Fe3+ ions are observed in EPR spectra of Pb1-xFexI2 nanocrystals.
Zn1-xMexO (Me- Mn, Co, Ni) thin films were grown by pulsed laser deposition and rf magnetron sputtering methods. The composite targets were formed by mixing and pressing of ZnO, Mn3O4, CoO and NiO powders. The thin films were deposited on sapphire, quartz and glass substrates. The structure study confirms the formation of the hexagonal wurtzite ZnO without any secondary phase in transition metal (Mn, Co, Ni) - doped samples. The surface morphology of the thin films was studied using atomic force microscopy (AFM). Different surface morphology AFM images were obtained depending on the film composition and growth conditions. Optical absorption spectra suggest of substitution Zn2+ ions in ZnO lattice by transition metal atoms. The shift of the absorption edge due to decrease the energy band gap with increasing cobalt content and complex dependence of the energy band gap on content of nickel was observed in optical absorption spectra of the studied films.
In this work, colloidal CdTe nanoparticles were synthesized by using thioglycolic acid (TGA) as passivator. In the absorption spectra of the colloidal CdTe nanoparticles exciton band was found to be shifted to higher photon energy as compared with bulk crystals due to quantum confinement effect. It was shown that addition of human serum albumin (HSA) to colloidal CdTe nanoparticles led to a gradual decrease of absorption and broadening of exciton structure. However, energy position of the exciton band in this case remains not shifted. In photoluminescence spectra of solution CdTe quantum dots and HSA so-called quenching effect has been observed. The quenching of HSA fluorescence intensity by semiconductor nanoparticles was analysed in framework of the formation of quantum dots-HSA protein complex.