NIR photoluminescence in Nd3+-doped gadolinium niobate nanophosphors modified by annealing, water, and PMMA media

Abstract

The photoluminescence (PL) and structural characteristics of neodymium-doped gadolinium niobate cube-like particles are studied as a function of annealing temperature. The hydrothermally as-prepared nanophosphors contain water which can be eliminated stepwise by low-temperature thermal treatment from 120 °C to 250 °C. This water, when remains in the structure after the annealing at 500 or 800 °C, results in an increased photoluminescence emission intensity up to a factor of 4.6, implying a water-assisted energy transfer mechanism. After the thermal treatment at 500 °C, the Nd3+-doped GdNb2O6 nanophosphors have an orthorhombic aeschynite crystalline structure and near-infrared (NIR) emissions at 881 nm (first biological window) and 1071 nm (second biological window). The annealing at 800 °C results in a mainly monoclinic GdNbO4 structure with NIR PL emissions at 890 and 1065 nm. The studied NIR PL emissions are associated with interelectronic energy levels of the Nd3+ ion, excited with either 358, 586/590, or 808 nm. Given the nanoscale characteristics of these Nd3+-doped particles, they can be readily dispersed in the polymeric media, such as poly (methyl methacrylate) (PMMA), forming a strong interaction between the Nd3+-doped GdNb2O6 nanophosphors and the PMMA matrix. This interaction assists in the energy transfer to the Nd3+ ions, leading to an increase in the NIR PL emission intensity by a factor of 8. In the case of the homogeneous Gd1-xNdxNb2O6/PMMA films, the 881 nm emission peak (4F3/2 → 4I9/2 transition) is the dominant one for the 281/251 nm excitation wavelengths. These results indicate that the neodymium-doped gadolinium niobates cube-like nanophosphors have great potential to be incorporated into a wide variety of applications.