Luminescence of the surface nonbridging oxygen hole center in silica: Spectral and decay properties

Abstract

We investigated the red luminescence in a porous film of silica nanoparticles, originating from surface nonbridging oxygen hole centers. The excitation spectrum was measured from 1.8 to 8.0 eV by a tunable laser system and a synchrotron radiation source; this spectrum evidences a peak at 2.0 eV, nearly overlapping with\ud the emission, and an ultraviolet broadband with peaks at 4.8 and 6.0 eV. The emission is characterized by a spectrum with two subbands split by 0.07 eV, its decay occurs with lifetime longer than 30 microsec and undergoes\ud a thermal quenching by a factor aboout 2 with increasing temperature from 10 to 290 K. The optical characteristics of surface and bulk centers are discussed on the basis of the reported experimental results and quantum\ud chemical calculations

Ni‐Catalyzed Growth of Silica Nanowires From Amorphous Silicon Films and Growth Mechanism

“…For both parts, the atomic concentrations of Si and O were found to be ≈30 and ≈69 at.%, respectively, yielding an approximate SiO 2 composition. The PL spectrum, likewise, shows a peak emission wavelength of approximately 430 nm, which is in good agreement with that observed for SiO 2 . Finally, the Si 2p core‐level XPS spectrum of NWs contains only a SiO 2 XPS peak, also demonstrating that the NWs have the composition of SiO 2 .…”

Vibrational properties of the surface-nonbridging oxygen in silica nanoparticles

“…Figure 1 shows the effects of temperature on time resolved PL spectra of surface-NBO centers measured with E ex = 1.997 eV. At T = 290 K the emission is characterized by two subbands peaked at 1.92Ϯ 0.01 and 1.99 Ϯ 0.01 eV, 16 and it extends over the anti-Stokes region. On lowering T, the PL amplitude increases, the anti-Stokes part vanishes and, below 150 K, the ZPL resonant with the excitation is increasingly evident together with vibrational structures.…”

“…We also note that the calculated values lead to a Stokes shift smaller than 2S tot ϫបϷ 0.05 eV in good agreement with the experimental results on the emission/excitation spectra of the surface-NBO center. 16 The most significant features of the local vibrations coupled to the electronic transition around 2 eV are derived by the emission spectra reported in the upper and lower sides of Fig. 2.…”

Visible luminescence peculiar to sintered silica nanoparticles: Spectral and decay properties

“…Therefore, we address its origin on the basis of the comparison with the luminescence properties of other silica based materials. It is well known that a PL centered at 1.9 eV with a lifetime in the μs timescale is associated with a dangling oxygen defect, also called nonbridging oxygen hole center (NBOHC) [25,26], which can be induced both in the bulk (by irradiation) [27] and at the surface of silica nanoparticles (by thermochemical reactions [26] or by irradiation [5]). However, its spectroscopic features are well distinguishable from those observed in the present work, so that we rule out the NBOHC as the origin of the red band in the sintered silica.…”