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Absorption spectra of Si2, Ge2, and Sn2, observed between 50 and 5000 cm−1 in neon and argon matrices at 4 K, were assigned to the lowest 3Πu←X 3Σg− electronic transition. In all three cases, the Franck–Condon envelope of vibrational bands allowed T00, ωe′, ωe′xe′ to be determined. In the Si2 molecule [near Case (a)] T00=313 cm−1 and each vibrational band was split into Ω triplets (0,1,2) in the upper state. A Zeeman effect on these lines was detected in magnetic fields up to 4 T. As the spin–orbit coupling becomes larger in Ge2 and Sn2, the 1u←X0+g transition [case (c)] was observed, and the corresponding parameters in the upper state determined. For Sn2 the magnetic-dipole 1g←X0+g transition was also detected and identified by the splitting and broadening of the band in magnetic fields up to 4 T. The results are discussed in the context of the ab initio calculations and other experimental results on these molecules.

The green emission in ZnO can be identified as two characteristic emissions, namely high and low energy emissions, respectively. The study of band bending effect of ZnO surface demonstrates that oxygen vacancies cause both the core level and the valence band to shift to higher binding energy. The downward band bending induced by a strong accumulation layer, where the oxygen vacancies act as donors, results in the high energy green emission. ZnO with the low energy green emission has Zn 2p 3/2 core level binding energy shifted to lower binding energy. The depth of dominant oxygen vacancies plays an important role in determining the mechanisms of green emission.