Polymer-salt synthesis of nanoscale Gd$_{2}$O$_{3}$:Nd$^{3+}$ phosphors and characterization of their basic properties

The article considers the aspects of nanoscale Gd$_{2}$O$_{3}$:Nd$^{3+}$ phosphors synthesis using the liquid polymer-salt method. Within the framework of the method, the double role of polyvinylpyrrolidone (PVP) as an organic solvent in the process of synthesis was determined. On the one hand, PVP stabilizes the process of Gd$_{2}$O$_{3}$ crystals formation, preventing their uncontrolled growth and aggregation. On the other hand, PVP serves as a fuel during decomposition (combustion) increasing the temperature of reaction and thus influencing the structural and emission properties of phosphors. It is shown that drying of the initial homogeneous solution containing gadolinium and neodymium salts and PVP at the room temperature for 24 hours followed by thermal treatment at the temperature of 1000$^{\circ}$C for 2 hours allow formation of highly luminescent Gd$_{2}$O$_{3}$:Nd$^{3+}$ near-infrared phosphors. The crystals grown are characterized mainly by the cubic structure and an average size of 40 nm. Experimental results confirmed that the developed method is appropriate for modification of a structure of silica hollow-core antiresonant fibers with thin-film coatings based on the synthesized material and does not result in structural and phase conversion of Gd$_{2}$O$_{3}$ crystals. It is found out that emission spectra of nanoscale Gd$_{2}$O$_{3}$:Nd$^{3+}$ phosphors formed by the polymer-salt method at the temperatures of 550$^{\circ}$C and 1000$^{\circ}$C are identical, as follows: 1) the shape of the luminescence peaks is the same for the two mentioned regimes of thermal treatment regardless of intensity, 2) the main luminescence peak is located near the wavelength of 1064 nm and corresponds to a $^{4}F_{3/2}$–$^{4}I_{11/2}$ electron transition, 3) additional luminescence peaks are located close to 900 nm and 1340 nm and refer to $^{4}F_{3/2}$–$^{4}I_{9/2}$ and $^{4}F_{3/2}$–$^{4}I_{13/2}$ electron transitions respectively.