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

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 similar to 13 nm Gd2O3 shell was successfully coated onto similar to 220 nm monodispersed SiO2 nanocores. Concentrations of similar to 20 at% Eu3+ in the SiO2/Gd2O3 nanoparticles exhibited photoluminescent (PL) emission from the D-5(0)-F-7(2) transitions of Eu3+ at 609 and 622 nm after being calcined at 800 degrees 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.