Spectroscopic Properties and Orange-Red Emission of Sm3+-Doped SWN Glasses for LED Applications.

Sm3+-doped antimony-tungsten-phosphate glasses (designated SWNSm) with the composition (40 - x) Sb2O3-10WO3-50NaPO3-xSm2O3 (x = 0.15, 0.30, 0.45, 0.60, and 0.75 mol%) were prepared by the conventional melt-quenching-annealing technique. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses confirmed the amorphous nature and excellent thermal stability of the prepared glasses. Both experimental and theoretical elastic parameters, including Young's modulus (E) and Poisson's ratio (ν), were evaluated to verify that the incorporation of Sm3+ ions does not compromise the mechanical stiffness of the host glass. The measured density increased with increasing Sm2O3 content. Vibrational modes were identified using IR and FTIR spectroscopy. The optical bandgap values for all glass compositions were determined to lie in the range of 2.84-2.87 eV, confirming the insulating character of these glasses. Under 402 nm excitation, the down-conversion emission spectra exhibited characteristic transitions: 4G5/2 → 6H5/2 (560 nm), 4G5/2 → 6H7/2 (596 nm), 4G5/2 → 6H9/2 (643 nm), and 4G5/2 → 6H11/2 (707 nm). The observed up-conversion luminescence was interpreted in terms of excited-state absorption (ESA), energy transfer (ET), and cross-relaxation (CR) mechanisms. IR analysis revealed that the low phonon energy of the antimony-based glass host-evidenced by the dominant Sb-O-Sb stretching band at 602 cm-1-results in a reduced multiphonon relaxation rate, thereby facilitating efficient up-conversion processes. With increasing Sm3+ content, the measured fluorescence lifetime decreased from 1.815 to 1.710 ms, which is attributed to the increased concentration of OH- groups and the enhanced probability of ET among Sm3+ ions. The CIE chromaticity coordinates (x, y) fall within the orange-red region, indicating that these glasses are promising candidates for orange-red LED and solid-state laser applications.