Physical, optical and thermal properties of erbium-doped borotellurite silicate glass system incorporated with silver oxide

Four series of rare earth doped borotellurite silicate glass were prepared by melt quenching method. The first and second series are a quaternary erbium oxide and erbium oxide nanoparticles doped glass with chemical composition {[(TeO2)0.8 (B2O3)0.2]0.8 (SiO2)0.2}1-y (RE)y, y= 0.01, 0.02, 0.03, 0.04, 0.05 molar fraction and RE = Er2O3 /Er2O3 NPs, while the third and fourth series are a multicomposition [{[(TeO2)0.8 (B2O3)0.2]0.8 (SiO2)0.2}0.99 (Ag2O)0.01]1-y (RE)y where y = 0.01, 0.02, 0.03, 0.04, 0.05 molar fraction.. This research proposes to extract silica from the rice husk and use it to synthesize a series of selected chemical composition of borotellurite silicate glasses doped with different concentration of Er2O3, Er2O3 nanoparticles (NPs) and doped with Ag2O in order to study their effects on the physical, structural, optical and thermal properties. Addition of Ag2O into the glass composition modifies the optical properties of the glass system. This will go a long way in turning waste into wealth. A novel type of glasses containing rare earth ions and silver ions has recently emerged and already attracted significant attention, the reason for such interest lies in the efficient enhancement of the fluorescent properties in rare earth doped glasses when appropriate silver ions is introduced to it. Results of X-ray diffraction (XRD) confirmed the amorphous nature of the glass. The X-ray fluorescence (XRF) verified the achievement of 98.6% of silicate from rice husk. Fourier transform infrared (FTIR) has revealed the basic structural units such as TeO4, TeO3, BO4, BO3, Si-O-Si and OSi- O in the glass system. The presence of erbium nanoparticles in the second and fourth series was verified from transmission emission microscopy (TEM) and the size of the nanoparticles were recorded within the range of 25 - 28 nm and 41 - 50 nm. The differential scanning calorimetry (DSC) measurements indicate a good thermal stability of borotellurite silicate glasses with the values of Ts > 100 oC, and the transition temperature, Tg in all the glass series are found to increase from 437 to 511 oC, 447 to 498oC, 452 to 482 oC and 469 to 495 oC with the increasing dopants concentrations in all the four glass series. The four glass series have a Hruby parameter (Hr) in the range of 0.32 – 0.51, 0.20 – 0.37, 0.55 – 0.64 and 0.47 – 0.64 greater than 0.4 which verified that the glasses were easily formed with moderate quenching rate. The reduced glass transition (Trg) are also within the range of 1⁄2 − 3⁄2. The DSC profiles show an improvement of thermal stability of the glasses with addition of Ag2O to 273 oC. The theoretical complications in understanding the structures and properties of amorphous solids are amplified by the lack of precise experimental information. Absorption spectrum from near infrared to visible light was obtained and the Judd– Ofelt (J–O) intensity parameters (Ωλ, λ = 2,4,6) were calculated. The calculated values of the parameters fall within the range of (4.178 to 6.507) × 10-20cm2, (1.384 to 2.143) × 10-20cm2 and (0.893 to 2.451) × 10-20cm2 for Ω2, Ω4 and Ω6 respectively. Also, the J-O parameter of Ω2 decreases from 5.366 × 10-20 cm2 to 4.529 × 10-20 cm2 and Ω6 from 1.349 × 10-20 cm2 to 1.212 × 10-20 cm2 with increasing Er3+ NPs/Ag concentration. Spontaneous emission probabilities of some important transitions, branching ratio, and radiative lifetimes of some excited states of Er3+ and Er3+ NPs are predicted using J– O intensity parameters. The branching ratio β for 4I15/2-2H11/2, and 4I15/2-4F9/2 transitions are within the range 65 – 95% indicating that there is a possibility for red and green emissions. The glass samples with 0.01 Er and 0.01 Er NPs for the two glass series exhibits the smallest value of τ which are 0.025 and 0.204 ms respectively corresponding to 2H11/2 → 4I15/2 transition. Absorption cross-section, calculated emission cross-section and gain, were evaluated using the McCumber theory for 4I13/2 →4I15/2 Er3+ transition. A schematic energy level diagram is proposed in this work. The full width at half maximum (FWHM), the gain band width (GBW) and figure of merit (FOM) for 4I13/2→ 4I15/2 transitions of the glasses have also been studied and reported. All the glass samples show a positive gain above 50% population inversion and the samples exhibit a flat gain bandwidth in the range of 1400 - 1700 nm, which covers the S band (1460 - 1530 nm) and C band (1530 - 1565 nm) in the optical communication window. The gain-bandwidth and gain cross-section profile suggest that these glasses could be found as more promising materials for broadband amplification of both S and C-band signals. The large values of thermal stability of the glass unveils that these glasses are stable against devitrification and are suitable for potential application in fiber drawing. The spectroscopic quality factors in the range of 0.79 – 1.87 and 0.29 – 0.43 for Er2O3 and Er2O3 NPs doped glasses and 0.48- 0.79 and 0.80-0.89 for the glasses incorporated with silver oxide obtained from the Judd-Ofelt parameters suggest the fact that the glasses are suitable for solid state laser application. The optimum concentration of dopants is achieved is achieved at 0.03 molar fraction as shown in the PL analysis of all the sample glasses. Beyond that concentration, the PL intensity begins to drop with increasing dopant concentration. In view of that, the glasses with 0.03 molar fraction are considered suitable for solid state laser application.

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