Luminescence of non-bridging oxygen hole centers in crystalline SiO2

Oxygen dangling bonds (nonbridging oxygen hole centers, NBOHCs), which are characteristic to amorphous SiO2, were studied in amorphized regions of neutron-irradiated α-quartz crystal and on their boundaries by time-resolved site-selective photoluminescence (PL) at 20K. Along with the usual disorder-broadened PL band of NBOHCs, sharp, 'crystal-like' zero-phonon lines (ZPLs), whose positions do not shift with the excitation wavelength, are observed. In addition to the previously reported NBOHCs with ZPL at 1.933 eV, a second sub-type of NBOHCs with ZPL at 1.883 eV is confirmed by observation of its vibrational sideband due to Si-(dangling O) stretching mode (897cm−1) under resonance 1.883eV excitation. A third sub-type of NBOHCs with an excitation energy at 1.879 eV, distinguished by a strong coupling to low-energy (66 cm−1) vibrational mode is found. This mode is weakly coupled also to the other two sub-types of NBOHCs.