Photoluminescence Spectra of β-Rhombohedral Boron

We report the detailed features of the photoluminescence (PL) spectra of a single crystal of β-rhombohedral boron (β-B) in the range of 900–1700 nm (0.73–1.38 eV). Broad spectra whose peak energy was 1.14 eV were observed. The peak energy corresponds to the recombination of an electron in a trapping level with a hole in the intrinsic acceptor level, which is characteristic of β-B and originates from the unique electronic structure of an icosahedral cluster B 12 . Temperature dependence of the PL intensity indicates that there are two thermal escape processes of electrons whose activation energies are about 0.10 and 0.004 eV. The former is attributed to the escape process of an electron from the electron trapping level to the conduction band. These results agree with the proposed band structure model based on the electronic structure of B 12 . PL decay measurement shows that there are two components with lifetimes of 4×10 -7 s and 5×10 -5 s.