Two-photon-excited luminescence and defect formation in SiO2 nanoparticles induced by 6.4-eV ArF laser light

Abstract

The photoluminescence ͑PL͒ from 7-and 15-nm silica (SiO 2 ) nanoparticles induced both by ArF laser light ͓ exc ϭ193 nm (6.4 eV), L ϭ15 ns͔ and by Nd:YAG ͑yttrium-aluminum-garnet͒ laser light ͓ exc ϭ266 nm (4.66 eV), L ϭ8 ns͔ was studied. The laser light intensity dependencies of the PL yields reveal the two-photon ͑TP͒ process of the PL excitation in the case of ArF laser light. The PL results from the radiative relaxation of self-trapped excitons ͑STEthe blue band͒, also from the surface hydrogen-related species ͑the green band͒, and the bulk nonbridging oxygen hole centers ͑NBOHC'sthe red band͒ excited by a radiationless relaxation of TP-produced free excitons ͑FE's͒. The main point is focused on the effect of the nanoparticle surface condition on the FE dynamics. The dynamics includes either an elastic scattering or quenching by the nanoparticle boundary, the laser heating of FE's up to energies in excess of the STE barrier, the FE energy transfer to the surface and bulk NBOHC's and hydrogen-related centers, the saturation of the FE density, and the biexciton process in the formation of Frenkel defects with their subsequent transformation into NBOHC's.

Water Radiolysis: Influence of Oxide Surfaces on H2 Production under Ionizing Radiation

“…In the case of high dose rate irradiation, the H 2 yields are much smaller than in the case of -irradiation with low dose rate; most of the received energy is not used for H 2 production but for recombination of excitons on defect sites (cathodoluminescence) or exciton-exciton reaction [90]. The accumulation of defects under irradiation can provide an additional deactivation pathway for excitons [91]: this is indeed the principle of cathodoluminescence spectroscopy [92]. Therefore, less excitons can reach the surface to induce H 2 production and the dihydrogen yields are then strongly decreased [90];  the LET value of the particles.…”

Theoretical prediction of atomic and electronic structure of neutral Si6Om (m=1–11) clusters

“…6 Since El-Shall and co-workers 7 observed bright blue photoluminescence in silica, different authors tried to justify the experimental observation by large concentration of oxygen defects related to the size of the lowest unoccupied molecular orbital-highest occupied molecular orbital ͑LUMO-HOMO͒ gap. 8 Silica clusters show light absorption 8 and photoluminescence 9 because their particular structures are very different from the conventional bulk material. Another interest is silica as a molecular building material, since the combination of its bulk stability and the advantage of its abundance put it in a very good position to be exploited via synthetic methods.…”

Thermal quenching properties of ultraviolet emitting centers in mesoporous silica

“…The blue emission reported in silica nanoparticles at about 2.7 eV is attributed to self-trapped excitons whose spectral features are affected by the nanoscale of the silica particles studied. [12][13][14] Experimental evidence was reported to claim the attribution of the green luminescence to H-or OH-related surface defects and the attribution of the red emission to surface nonbridging oxygen. [15][16][17] Beside the PL bands in the visible range, few articles have dealt with ultraviolet ͑UV͒ emissions observed in silicon oxide films, oxidized porous silicon, and mesoporous silica.…”