Niobium incorporation into rare-earth doped aluminophosphate glasses: Structural characterization, optical properties, and luminescence

Luminescent Rare Earth (RE3+) doped phosphate glasses with molar composition (1-x)(60P2O5 -15ZnO - 5Al2O3 - 10BaO - 10PbO)-xNb2O5 (x = 0, 10, 20 and 30 wt%) doped with 1.0, 1.2 and 0.3 wt% of Eu2O3, Yb2O3 and Er2O3, respectively, were prepared by conventional melt cooling. The glasses were characterized by optical reflectance, Raman scattering, and multinuclear (31P, 27Al, and 93Nb) solid-state NMR spectroscopy. Monotonic 31P chemical shift changes as a function of Nb2O5 content are consistent with the successive formation of Nb-O-P linkages. Aluminum is found in four-, five-, and six-coordination, with a successive decrease in average coor-dination number with increasing niobium content, while 93Nb NMR indicates three distinct niobium environ-ments in these glasses. Incorporation of Nb2O5 has the expected effects on refractive index values, optical basicity, optical electronegativity, Urbach Energy, and the indirect bandgap, while RE3+ emission properties are only slightly modified. Under UV excitation, narrow emission bands are observed arising from 5D0 -> 7FJ (J = 0, 1, 2, 3, and 4) transitions of Eu3+. At least two distinct Eu3+ lifetime values are observed, suggesting a spread of different ionic environments within the glass structure. Co-doping with Er3+/Yb3+ promotes emission in the infrared region, with a emission band maximum near 1535 nm and a width of 30.65 nm under excitation at 980 nm. Based on the results, these glasses may be potential candidates for energy conversion from infrared or UV region to the visible region and also infrared solid-state emitters.