Non‐radiative relaxation of excited states of non‐bridging oxygen hole centers in silica

Abstract

Processes involved in the excited-state relaxation of non-bridging oxygen hole centers (NBOHCs) were studied in glassy SiO 2 using luminescence, optical absorption and photoelectron emission spectroscopy. It was shown that photoexcited NBOHCs generally have three channels of relaxation. Along with radiative transitions responsible for the luminescence band at 1.9 eV, two non-radiative channels caused by transitions between levels of photoexcited state were observed. The first non-radiative channel was connected with transformation of the electron excitation energy to thermal lattice vibrations and represented an intracenter process of NBOHC luminescence quenching (the activation barrier was 0.05 eV). The second non-radiative relaxation channel for excited NBOHCs was identified as thermally activated external luminescence quenching with the energy barrier of 0.46 eV. As a result of realization of the specified process, the transfer of the excitation energy from NBOHCs to oxygen-deficient centers (ODCs) acting as electron emitters took place.

Phonon coupling of non-bridging oxygen hole center with the silica environment: Temperature dependence of the 1.9eV emission spectra

“…Regardless the excitation we obtain comparable parameters: E þ a ¼ 0.05070.004 eV, E À a ¼ 0.00270.001 eV, A ¼ 1672. We acknowledge that the upper limit agrees with that derived by Zatsepin et al [23] in temperature-dependence experiments carried out above 100 K.…”

Point defects and interference effects in electron emission of Si/SiO2:Li,Na,K structures

“…Therefore, we cannot see the proper contribution of deeper emission sites in the spectra. On the other hand, the optical absorption measurements for the alkali‐silicate glasses reveal quite close slopes of 0.12–0.125 eV . Higher values shown in Table may be explained by different types of electron transitions responsible for absorption and electron emission.…”