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The photoluminescence from ZnTe : Yb films grown on (100) GaAs by MBE was studied at different temperatures (4.2-350) K. The efficient Yb 3þ -related emission in ZnTe was observed up to room temperature. The analysis of the fine structure of the Yb luminescence spectra allowed us to suggest the energy level diagram of the crystal-field-split 4f 13 levels for the dominant complex center based on Yb ion. IntroductionThe basis of possible applications of RE-doped semiconductors such as light emitting devices is the opportunity to combine the sharp, temperature stable, atom like emission due to radiative transitions in the unfilled 4f n shell of rare-earth (RE) ions with the advantages of electrical pumping in semiconductor structures. Optical properties of RE element doped semiconductor have been widely studied, but the luminescence efficiency is still rather low and the intensity rapidly decreases at high temperatures. Intensity of f-f luminescence in RE doped semiconductors is determined by following factors: total amount of RE luminescence centers, general quality of RE doped crystals which determines the efficiency of competing non-radiative processes, efficiency of energy transfer from electron and holes to RE luminescent centers, probability of optical transitions within 4f shell of RE centers. The latter two characteristics depend upon the structure of luminescence centers, that is on the lattice position of RE impurity and its possible association with other impurity and/or defects. Due to high chemical activity of RE elements, their associations with other chemical dopants are quite common. It is known that co-doping of RE in II-VI compounds is a prerequisite for their optical activity and photoluminescence efficiency of RE in ionic hosts is usually highest for RE complexes [1]. In the present work the studies of the luminescence properties of Yb doped ZnTe grown by MBE were carried out in a wide temperature range in order to determine the conditions required for attainment of efficient RE emission. The advantage of MBE growth of II-VI compounds is the rather low temperature of their synthesis, which grants a low desorption rate of adsorbed RE atoms from a substrate surface during MBE and efficient Yb incorporation into the host crystal which is a prerequisite for the production of RE emitting material.

Polycrystalline CVD diamond has been annealed in vacuum at temperatures tan = 1550 °C–1690 °C to investigate an influence of modifications of grain boundaries (GB) and defects on thermal conductivity and optical properties of originally optical quality material. While the sample was converted by this heat treatment to “black diamond”, excitons still could be observed in cathodoluminescence spectra. Photoluminescence spectra revealed an aggregation of nitrogen (formation of H3 optical center) after annealing at 1690 °C. In‐plane thermal conductivity k (T) measured by a heated bar method in the temperature range T = 5–410 K shows a strong (up to 5 times) and monotonic decrease at T < 45 K upon annealing, while room temperature k (298 K) value remains almost constant (ca. 19.0 W/cm K) till tan = 1650 °C, rapidly degrading at higher tan. The experimental data on thermal conductivity are analyzed in the framework of full Callaway theory taking into account three‐phonon scattering processes, phonon scattering on point defects, sample boundaries, and GB. The proposed model reproduces well the observed k (T) behavior, the phonon scattering on the modified GB playing an important role. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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