Optical spectra and judd-ofelt analysis of dysprosium and samarium impurities activated strontium magnesium borate glasses

Abstract

New types of strontium magnesium borate glasses namely Dy3+- and Sm3+- singly activated and D y + Sm3+- co-doped with the nominal compositions of 20SrO - lOMgO - (70 - x) B2O3 - JtDy20 3 (0.1 < jc < 0.8 mol%); 20SrO - lOMgO - (70 - y) B2O3 - jSm203 (0.5 < y < 2.5 mol%) and 20SrO - lOMgO - (70 - z) B2O3 - 0.7Dy203 - ZS1T12O3 (0.2 < z < 1.0 mol%) were prepared by the melt-quenching method. The structural properties of the quenched glass samples were investigated using X-Ray diffraction (XRD), Fourier Transform Infrared (FTIR), Energy Dispersive X-ray (EDX) analyses and Field Emission Scanning Electron Microscope (FESEM) respectively. The Ultraviolet-Visible-near-IR Spectroscopy (UV-Vis-NIR) spectra of the glasses exhibited characteristic absorption transitions of Dy3+ and Sm3+ respectively. The nephelauxetic effect on the absorption transitions has been used to elucidate the bonding nature of the doping ions with the surrounding ligands revealing the predominant ionic nature. The photoluminescence (PL) emission spectra analysis of the Dy3+-doped glasses revealed three peaks including blue at 483 nm, yellow at 575 nm and red at 664 nm attributed to 4f-4f transitions. The glass made with Dy203 content of 0.7 mol% revealed optimum PL intensity and this composition was chosen for co-doping with various S1T12O3 contents. The PL spectra for Dy3+ / Sm3+ co-doped glass system exhibited five emission bands due to the 4F9/2—»6Hi5/2 (Dy3+), 4F9/2—>6Hi3/2 (Dy3+), 4G5/2—>6H7/2 (Sm3+), 4G5/2—»6H9/2 (Sm3+) and 4Gs/2—>6Hi 1/2 (Sm3+) transitions in Dy3+ and Sm3+, respectively. The luminescence spectra of Dy3+ / Sm3+ co-doped glasses revealed that the successive addition of Sm3+ to Dy3+-doped strontium magnesium borate glasses has enhanced the emission intensity of Dy3+ with decreased emission intensity of Sm3+ at 0.4 mol% in Dy3+ + Sm3+ co-doped glasses due to strong migration of Sm3+ excitation energy to Dy,+. From the optical absorption measurements and based on Judd-Ofelt theory (J-O), the influence of Dy3+ and Sm3+ on the three J-O intensity parameters (Q2, Qa, Q6) were evaluated. The achieved values of intensity parameters were used to calculate the J-O radiative properties including the branching ratio, stimulated emission cross-section, optical bandwidth and optical gain. The achieved high values of the branching ratio (> 60% and 74%) and stimulated emission cross-section (> 10 x 10-22 cm2) recorded at 4F9/2-> 6Hi3/2 and 4G5/2 —> 6H7/2 electronic transitions showed an excellent lasing and optical energy harnessing potentials of the proposed glass compositions. The observed increase in optical gain envisages an effective lasing efficiency and optical amplification power of the glass samples for low threshold amplifier design and solid-state laser development.