Structural and Luminescence Properties of (Gd1−xYx)2O3 Powders Doped with Nd3+ Ions for Temperature Measurements

Abstract

Rare earth activated powders are widely regarded as promising candidates for optical thermometry due to their unique photoluminescence characteristics. The paper presents the structural and luminescent properties of crystalline powders of gadolinium and yttrium oxides (Gd1−xYx)2O3, doped with Nd3+ ions, synthesized by the liquid polymer-salt method. The addition of polyvinylpyrrolidone increases the homogeneity of the mixture and ensures high adhesion of the resulting powders. Scanning electron microscopy shows that powders are μm-sized aggregates, which consist of particles with several tens of nanometers in size. A smooth shift of the diffraction peaks of the powders occurs when Gd is replaced by Y without additional peaks. The successive decrease in the lattice constant of the powders from 10.816 to 10.607 Å confirms the existence of continuous solid solutions in the system. The Stark sublevels of the 4F3/2 → 4I9/2 fluorescent band are shifted to 4 nm when Gd is replaced by Y since the strength of the local field has a stronger effect on the inner F-shell of Nd ions in the case of Y. For thermometry, we chose the ratio of the fluorescence intensities between the Stark sublevels 4F3/2(2) → 4I9/2(2) and 4F3/2(1) → 4I9/2(2). The best obtained sensitivity is 0.22% °C−1 for Nd-doped GdYO3 powder in the range of 10–70 °C. This value of temperature sensitivity, together with radiation and excitation lying in the biological window, opens the possibility of using Nd3+-doped (Gd1−xYx)2O3 powders for real-time thermal probing of under tissue luminescence with sub-degree resolution.