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

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. •The GdNb2O6 submicron particles doped with Nd3+ ions present intense PL emission in the NIR region.•The NIR PL emissions shift from 1071 to 1065 nm and from 881 to 890 nm with the increased annealing temperature from 500 to 800 °C.•Water inclusions in the Gd1-xNdxNb2O6 submicron particles lead to an increase in the Nd3+-related NIR PL emission intensity.•The Gd1-xNdxNb2O6 nanophosphors can be exited with a variety of wavelengths such as 358, 586/590, and 808 nm.•The Gd1-xNdxNb2O6 nanophosphors are readily dispersed in polymeric media, forming a strong interaction between the particles and the matrix.