Spectra and transients of the photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline Si/ SiO 2 multilayered structures with mean nanocrystal size of 1.5-4.5 nm have been comparatively investigated. The Er-doped structures exhibit a strong Er-related PL band at 0.81 eV, while the efficiency of the intrinsic PL band of Si nanocrystals at 1.2-1.7 eV decreases by several orders of magnitude in comparison with the undoped structures. At low temperature the PL spectra of the Er-doped structures show several dips separated by the energy of Si TO-phonon and bound to the transition energies between the second and third excited states to the ground state of Er 3+. The Er-related PL is characterized by lifetimes of around 3-5 ms, a weak temperature quenching, and a high efficiency, which is comparable or even stronger than that of the intrinsic PL in the corresponding undoped samples. This efficient sensitizing of the Er-related luminescence is explained by the structural properties of the samples, which favor a strong coupling between the excitons confined in Si nanocrystals and upper excited states of the Er 3+ ions in the SiO 2 matrix.

Comparative studies of photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline Si/SiO2 superlattice structures show that the optical excitation of Si nanocrystals can be completely transferred to the Er3+ ions in surrounding SiO2, resulting in a strong PL line at 1.5 μm. The PL yield of the Er-doped structure increases for higher photon energy of excitation and for smaller nanocrystal sizes. This highly efficient sensitizing of the Er-related PL is explained by a strong coupling between excitons confined in Si nanocrystals and neighboring Er3+ ions in their upper excited states.

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ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb 2 O 3 , P, As, Sb and Zn 3 X 2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of V Zn and V Zn -complexes was confirmed and their concentrations were measured. Estimates of the number of V Zn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb) Zn -2V Zn commonly regarded as responsible for acceptor properties in ZnO.

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