Photoluminescence of Sn-doped SiO2 excited by synchrotron radiation

Changes in the photoluminescence (PL) of amorphous SiO2 due to Sn-doping have been investigated by synchrotron radiation. Sn-doped SiO2 samples have been produced by a controlled sol–gel procedure as well as Ge-doped samples prepared for comparison. Detailed maps of the PL and PL excitation pattern have been obtained up to the band-to-band transition energy. The results confirm the analysis of Skuja as regards the emission at 3.1 and 4.2 eV excited at about 5 eV. At higher energies, our data show that the 3.1 and 4.2 eV PL bands have another excitation region with structures at 6.7, 7.2 and 8.0 eV. Lifetimes of about 10 ns for the 4.2 eV PL and 10 μs for the 3.1 eV PL are observed independently of the excitation energy. Data between 10 and 300 K are presented and compared with data from Ge-doped samples. The results show that high energy excitation of the 3.1 eV PL is not thermally activated, in contrast to the 4.9 eV excitation channel. Effects of the different spin–orbit coupling constants at Ge and Sn sites on PL intensity suggest that the high energy excitation channels arise from intra-center singlet-to-singlet transitions.