Thermodynamic model for the structure of Nd doped phosphate laser glasses and the neodymium chemistry influence on their emission properties

• The structure of Nd metaphosphate glasses can be obtained by thermodynamic modeling. • A close link exists between predicted and experimental P-O-Al bonds of the network. • Nd chemical environment resembles that in alkaline neodymium metaphosphate crystals. • Glasses with Nd in K2NdP5O15 metaphosphates show the best optical properties. • Increased asymmetry of Nd3+ chemical environment enhances emission properties. Development of phosphate laser glasses has focused on combining good laser emission with high mechanical performance and their structure has increasingly been of importance due to the usefulness in interpreting the behavior of functional glasses and help in the design of novel compositions. Herein we tackled the interrelationships between the structure, the nearby chemical environment of Nd 3+ ions and the spectroscopic and laser emission properties in a series of phosphate and alumino-phosphate Nd-doped glasses. The structure has been obtained using the associated solutions model and has been confirmed by a multinuclear NMR study in the system Na 2 O-K 2 O-BaO-Al 2 O 3 -P 2 O 5 , then correlated with the emission properties of the different glasses. Nd luminescence depends on the coordination around Nd and linear and nonlinear spectroscopic results suggest that high strength modifiers in mixed-alkali compositions increase the crystal field disorder enhancing electric-dipole transitions and promoting the presence of two broad distributions of Nd 3+ sites.