Synthesis of hexagonal phase Gd2O2CO3:Yb3+, Er3+ upconversion nanoparticles via SiO2 coating and Nd3+ doping

By SiO2 shell coating and Nd3+ doping, layer-structured hexagonal phase Gd2O2CO3:Yb3+, Er3+ nanoparticles were synthesized successfully through a homogeneous precipitation method. The detailed mechanism was investigated and the results indicate that the SiO2 shell and Nd3+ doping ions can effectively prevent hexagonal phase Gd2O2CO3 from decomposing into cubic phase Gd2O3 during heat treatment, because the SiO2 shell limits the diffusion of CO2 gas and the Nd3+ doping increases the decomposition temperature of Gd2O2CO3. Compared with non-layer-structured GdVO4:20%Yb3+, 2%Er3+, 4%Nd3+ particles with similar diameters and morphologies and lower phonon energies, layer-structured Gd2O2CO3:20%Yb3+, 2%Er3+, 4%Nd3+/SiO2 hexagonal phase particles show much a stronger upconversion emission, suggesting that layer-structured materials are more appropriate as upconversion hosts. Furthermore, the paramagnetic properties of Gd2O2CO3:Yb3+, Er3+, Nd3+/SiO2 nanoparticles were also demonstrated.