Thermal quenching properties of ultraviolet emitting centers in mesoporous silica

Abstract

We report an investigation of the thermal quenching properties of the ultraviolet emission observed in mesoporous silica. The optical emission is due to the contribution of two emitting centers at 3.7 and 4.0 eV and previously assigned to strong-and weak-interacting silanols ͑Si-OH͒ located at the surface of the material. We investigate the temperature dependence of the lifetimes and the photoluminescence amplitudes of the two centers, in the 10-300 K range, by exciting in the ultraviolet and vacuum ultraviolet region with synchrotron radiation. The analysis of the lifetimes, carried out in the framework of a biexponential model at all the temperatures and excitations, and of the temperature dependence of the photoluminescence amplitude displayed different quenching properties in samples with different pore diameters. In addition, the thermal dependence of the photoluminescence amplitudes shows a distribution of the activation energy as a function of the emission energy in samples with smaller pore diameter.

Luminescence properties of nonbridging oxygen hole centers at the silica surface

“…In agreement with Fig. 1, these variants differ by the structure adjacent to the Si coordination sphere: in the first, ("Si-O) 3 Si-O , each ligand O is bonded to two Si; in the second, ("Si-O) 2 (H-O)Si-O , one of the ligand O atoms is terminated by a H. Our purpose is to examine the influence of these specific structures on the spectroscopic features (spectrum lineshape, lifetime and luminescence quantum yield) thus providing a clue to clarify the origin of the optical transitions associated with the NBOHC.…”

“…The very high specific surface area of such systems ( J 10 2 m 2 /g) favors a large concentration of surface structural defects that play a crucial role in controlling the optical and electrical properties of silica nano-devices [1][2][3][4]. One of the most common defects at the silica surface is the oxygen dangling bond or nonbridging oxygen hole center (NBOHC) [5][6][7][8][9] whose structure is denoted by "Si-O , where (") stands for bonds with three oxygen atoms and () indicates an unpaired electron.…”

On the origin of blue and UV emission bands in mesoporous silica

“…This is also confirmed by the data reported in Fig.2 where the different contribution of the two bands in samples with different porosity is shown as a function of the temperature [27]. The dependence on the temperature was further studied to ascertain the presence of multiple contributions for both the bands and to study the activation energy for both of them [50]. The general picture is that there are two different distributions of defects for both the UV and blue band, which can be ascribed to two different kinds of surface defects.…”

“…To go further in the investigation we analyzed the effects of long air exposure, sample storing under high vacuum conditions and gas purging [34,35,[49][50][51]. This analysis allowed us to exclude that the UV band could be related to carbon impurities.…”

Silver nanoparticle (AgNPs) doped gum acacia–gelatin–silica nanohybrid: An effective support for diastase immobilization

“…gum acacia and gelatin. UV band is related to the relative content of silanol species present at the silica surface [49]. The red band [50] is due to quantum confinement possibly supplemented by surface states.…”