[en] Twenty five petrographically characterized chondrules, including 18 barred olivine (BO) chondrules from the Allende (CV3) meteorite, were analyzed for alkalis (K and Rb) and alkaline earths (Sr, Ba, Ca and Mg) by mass spectrometric isotope dilution. Most BO chondrules with higher alkalis (greater than the CI level) have nearly CI-chondritic Rb/K ratios, while those with lower alkalis clearly show higher Rb/K ratios than the CI-chondritic. In general, BO chondrules with higher Rb/K exhibit more depletion of alkalis relative to Ca. The mean olivine Fa for individual chondrules positively correlates with bulk alkali concentrations in BO type but not in porphyritic type chondrules. These observations suggest that some BO chondrules formed from more reducing assemblages of precursor minerals, which experienced more intensive vaporization losses of alkalis, accompanied by Rb/K fractionation, during the chondrule-formation melting. 30 refs

[en] Europium doped Ga₂O₃ films were deposited on sapphire substrates by using pulsed laser deposition. The influences of substrate temperature on structural and optical properties have been systematically investigated by means of X-ray diffraction and photoluminescence. High quality single (−201) oriented Ga₂O₃ film can be obtained at substrate temperature of 400 °C. The emission intensity of Eu³⁺ decreased solely with elevated temperature by using 325 nm light, while it had a maximum value at a certain temperature under 488 nm light. Both of the experimental data were well fitted by the luminescence dynamic equation models, suggesting that the variation of the emission intensity may be attributed to the thermal activated distribution of electrons among ⁷F_j and thermal quenching effect.

[en] Erbium doped Ga_2O_3 thin films were deposited on Si substrate by pulsed laser deposition method. Bright green emission (∼548 nm) can be observed by naked eye from Ga_2O_3:Er/Si light-emitting devices (LEDs). The driven voltage of this LEDs is 6.2 V which is lower than that of ZnO:Er/Si or GaN:Er/Si devices. Since the wide bandgap of Ga_2O_3 contain more defect-related level which will enhance the effects of recombination between electrons in the defect-related level and the holes in the valence band, resulting in the improvement of the energy transfer to Er ions. We believe that this work paves the way for the development of Si-based green LEDs by using wide bandgap Ga_2O_3 as the host materials for Er"3"+ ions.