Radiative recombination in GaN nanocrystals at high intensities of optical excitation

International audienceThe spectra of spontaneous UV luminescence of GaN nanocrystals excited by optical pumping at power densities ranging from 50 W/cm(2) to 50 MW/cm(2) are studied. At room temperature, radiation peaks related to the emission of free excitons and recombination of electron-hole plasma are revealed. The spectral characteristics of the emission of the electron-hole plasma in GaN is studied in the wide temperature range of 77-550 K. (c) 2005 Pleiades Publishing, Inc

Spontaneous and stimulated UV luminescence of ZnO : N at 77 k

International audienceThe spontaneous and stimulated UV luminescence spectra of ZnO:N samples possessing different nitrogen contents are measured at a temperature of 77 K. Luminescence peaks resulting from bound and free excitons, biexcitons, and electron recombination via the nitrogen acceptor level are identified. The optical depth (123 meV) of the N-O impurity acceptor level is determined. It is established that stimulated UV luminescence originating from inelastic exciton interaction sets in as the optical pump power increases. (c) 2005 Pleiades Publishing, Inc

Stimulated luminescence of ZnO nanocrystals of different shape grown by the method of gas transport

International audienceThe influence of the shape and size of zinc oxide nanocrystals on the threshold and directionality of lasing in the UV spectral region is investigated. Columnar-shaped nanocrystals with hexagonal faceting must have a diameter of 100-200 nm to provide sufficient optical excitation power for nanoresonators; this is comparable with the absorption length of the exciting light. A mode structure of the laser emission directed preferentially along the axis of the hexagonal prisms is observed. Different lasing mechanisms are established for nanoprisms and nanopyramids with a hexagonal base. High homogeneity in shape and size of ZnO nanocrystals, and the dependence of these parameters on the conditions of gas transport synthesis are established by electron microscope methods

Opal-ZnO nanocomposites: Structure and emission properties

International audienceThe structure of opal-ZnO composites is studied by transmission electron microscopy and X-ray phase analysis. It is shown that, under thermal treatment of infiltrated samples, a solid-phase reaction proceeds at the opal-ZnO interface. As a result, zinc silicate beta-Zn2SiO4 and its high-temperature phase, willemite Zn2SiO4, are formed. The structure and emission properties of the nanocomposite are studied in relation to the degree of filling. For a sample subjected to 25 cycles of filling, luminescence controlled by the beta-Zn2SiO4 phase is detected in the blue spectral region (at 430 nm). The angular dependences of the luminescence and reflection spectra of an opal-ZnO composite sample subjected to four cycles of filling show the effect of suppression of a spontaneous emission of zinc oxide in the photonic band gap. (c) 2005 Pleiades Publishing, Inc