Structural and optical characterisation of silanised Dy-doped-Gd₂O₃ NPs

In this work, we studied the optical properties of Dy-doped Gd₂O₃ nanoparticles (NPs) before and after their APTES functionalisation. We obtained luminescent Dy@Gd₂O₃ NPs (0.5, 1, and 5% mol) using a modified polyol method. Our work describes their detailed structural analysis using FT-IR, XRD, HRTEM, TGA and XAS techniques. The results show that these systems present a crystalline structure with a body-centred cubic cell and particle sizes of 10 nm. The dopant position was inferred as substitutional, through XAS analysis at the M_4,5-edges of Gd and Dy and K-edge of O, and in C₂ sites, based on photoluminescence studies. There was sensitization of the luminescence by the matrix as shown by the emission increase of the hypersensitive transition (⁶F_9/2 → ⁶H_13/2, 572 nm) and also a broadband appears around 510 nm attributed to defects in Gd₂O₃. An enhanced emissive lifetime of 398 μs was found for the sample doped at 1%. We functionalised the Dy@Gd₂O₃ (at 1%) NPs with 3-aminopropiltrietoxisilane (APTES) for further application as a biomarker sensor. We found that these NPs conserved their luminescence after adding the surface agent (avoiding quenching effects) making them potential materials for biosensing.