Multimodal luminescence spectra of ion-implanted silica

Abstract

The main luminescence bands in silica SiO₂ are the red luminescence R (650 nm, 1.9 eV) of the non-bridging oxygen hole center, and the blue band B (460 nm, 2.7 eV) and ultraviolet luminescence UV (290 nm, 4.3 eV), both commonly related to oxygen-deficient centers. In the present work, we will enhance or replace either the first or second constituent of SiO₂, i.e., silicon or oxygen, isoelectronically by additional implantation of the respective ions. Thus, thermally oxidized SiO₂ layers have been implanted by different ions of the IV group (C, Si, Ge, Sn, Pb) and of the VI group (O, S, Se) with doses up to 5 × 10¹⁶ cm⁻², leading to an atomic dopant fraction of about 4 at % at the half depth of the SiO₂ layers. Very surprisingly, the cathodoluminescence spectra of oxygen-and sulfur-implanted SiO₂ layers show, besides the characteristic bands, a sharp and intensive multimodal structure beginning at the green region at 500 nm up to the near infrared. The energy step differences of the sublevels equal on average 120 meV, and indicate vibration associated electronic states, probably of O ⁻₂ interstitial molecules.