Synthesis and luminescent characteristics of europium dopants in SiO2/Gd2O3 core/shell scintillating nanoparticles

Abstract

Scintillating nanoparticles with a SiO2 core and a Gd2O3 shell, where either the core or the shell was doped with Eu3+, were synthesized with a solution precipitation process. Based on transmission electron microscopy (TEM) data, an ∼13 nm Gd2O3 shell was successfully coated onto ∼220 nm mono-dispersed SiO2 nanocores. Concentrations of ∼20 at% Eu3+ in the SiO2/Gd2O3 nanoparticles exhibited photoluminescent (PL) emission from the 5D0-7F2 transitions of Eu3+ at 609 and 622 nm after being calcined at 800 °C for 2 h. The SiO2 remained amorphous after calcining, while the Gd2O3 crystallized to a cubic structure. Photoluminescence excitation (PLE) data showed that emission from Eu3+ could result from direct excitation, but was dominated by the oxygen to europium charge-transfer band (CTB) between 250 and 300 nm. The quantum yield (QY) from SiO2/Gd2O3:Eu3+ core/shell nanoparticles excited at wavelengths in the CTB decreased from 25.0% to 16.5% with addition of a SiO2 shell to form a SiO2/Gd2O3:Eu3+/SiO2 nanostructure. In contrast, the QY increased to 32.2% from a SiO2/Gd2O3:Eu3+/Gd2O3 nanostructure. This increased luminescence with a Gd2O3 surface shell is attributed to reduction of surface quenching sites. Moreover, for a SiO2:Eu3+ core, addition of a Gd2O3 capping layer increased the PL intensity by four times, which was attributed to the crystalline Gd2O3 layer also acting as an antenna for energy transfer to the SiO2:Eu3+ core.