Synthesis and Upconversion Luminescence of Nanoparticles Y2O3 and Gd2O3 Co-doped with Yb3+ and Er3+

Upconversion nanoparticles (UCNs) find application in nanomedicine as biolabels to identify cancer cells. In this work, Y2O3: Er3+/Yb3+ and Gd2O3: Er3+/Yb3+ systems were fabricated by combustion synthesis (CS) and sol-gel (SG) methods to obtain nanoparticles with different shapes and sizes after post-annealing treatments. The crystallinity and morphology were analysed by x-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively, and the luminescent properties by spectrofluorescence measurements. The luminescence varied depending on the doping level. In this study, for the host Y2O3, with Er3+/Yb3+ (1%/1% mol), the green emission was more strongly attributed to the H-2 (11/2)-> I-4 (15/2), S-4 (3/2)-> I-4 (15/2) transitions of Er3+ ions. Red emission was present in Yb3+ (5%/10% mol) due to the F-4(9/2)-> I-4(15/2) transition for both hosts. For the host Gd2O3, green emission was present in Er3+ (2% mol) and Yb3+ (3% mol). The surface of some UCNs was coated with a thin silica layer and analysed in order to compare the luminescence with the uncoated UCNs. The purpose of the coating was to prepare the samples for further functionalization for biolabel use. Results show that the emission intensity of all samples strongly depends on the synthesis method. SG was more reliable than CS synthesis in producing UCNs with better morphology and luminescent properties.