Nanocrystal-size selective spectroscopy in SnO2:Eu3+ semiconductor quantum dots

Abstract

Glass ceramics of composition $95{\mathrm{SiO}}_2\text{-}5{\mathrm{SnO}}_2$ doped with $0.4\mathrm{mol}\%$ ${\mathrm{Eu}}^{3+}$ have been prepared by thermal treatment of sol-gel glasses. The segregated ${\mathrm{SnO}}_2$ nanocrystals present a mean size comparable to the bulk exciton Bohr radius (about $2.4\mathrm{nm}$ ), corresponding to a wide band-gap quantum-dot system in an insulator ${\mathrm{SiO}}_2$ glass. A fraction of the ${\mathrm{Eu}}^{3+}$ ions is incorporated to the ${\mathrm{SnO}}_2$ nanocrystals in the process. In these strong confinement conditions, the energy gap presents a high dependence on the nanocrystal size. Taking advantage of this effect, it has been possible to excite selectively the ${\mathrm{Eu}}^{3+}$ ions located in the ${\mathrm{SnO}}_2$ nanocrystals, by energy transfer from the host, obtaining emission spectra that depend on the nanocrystal size. The ${\mathrm{Eu}}^{3+}$ ions environment in small nanocrystals (radius under $2\mathrm{nm}$ ) are very distorted, meanwhile they are like crystalline for nanocrystals with a radius of some nanometers.