Spectroscopic properties of lithium borate glass containing Sm and Nd ions

Received Jan 24, 2020 Revised Apr 23, 2020 Accepted May 11, 2020 Lithium borate glass samples mixed with a different concentration of Sm+ and Nd ions organized by quenching technique. Structural, vibration groups and spectral properties of glass samples investigated using X-ray diffraction, FTIR, UV/Vis/NIR and photoluminescence spectroscopy. The X-ray confirmed the lithium borate glass samples containing Sm and Nd ions in the amorphous state. Luminescence spectra of glass samples excited at 400 nm recorded, here three luminescence bands observed in Visible region, which due to spectra materials (Sm3+, Nd3+). These indicate that these glass samples responsible orange emission and used in the improvement of materials for LED, and optical devices. The functional vibration groups of the glass matrix studied using FTIR spectroscopy.

From the mentioned above and other many studies of synthetic and optical and physical properties have made on different types of glass groups containing component Nd 3+ or Sm 3+ . But there have few studies of their presence together in the glass samples. The effect of changing the ratio of one of them with the stability of the ratio of the second element studied. It found that the emission intensity decreased by increasing the ratio of Nd 3+ with the constant of Sm 3+ . As well as the emission intensity increase with increasing of Sm 3+ and constant of Nd 3+ content [25,26].
In this study, we study the effect of replacing Sm 3+ by Nd 3+ on the structural, thermal, optical, spectroscopic properties of Sm 3+ and Nd 3+ ions on this glass. Judd-ofelt parameters calculated, for observed absorption spectra for Sm 3+ and Nd 3+ ions as well as the emission intensity.

EXPERIMENTAL WORK
Sm +3 and Nd 3+ doped ion synthesized in the Borate glass system by conventional melt quenching method. The starting chemicals used reagent grade of H3BO3, Li2CO3, Sm2O3, and Nd2O3 with 99.99% purity. Chemical compositions prepared glasses as shown in Table 1. The mixture melted in porcelain crucibles at the 1100 O C for 2h. The structure of each sample confirmed amorphous by X-ray diffraction with a Phillips diffractometer PW3700 using CuKα1 radiation. The density measured using the Archimedes method. Optical absorption spectra of samples recorded using the UV-Vis spectrometer (Model-JASCO V570). The IR spectra of the glasses recorded using the FTIR 4100 JASCO spectrophotometer Michelson interferometer type in the wavenumber region from 400 to 2000 cm -1 . The Differential thermal analysis of glass samples carried using a SHIMADZUDTA-50 ANALYZER. The emission measure using Spectrofluorometer type JASCO-FP-6300. Figure 1 demonstrates the XRD of the prepared glass sample containing a different Nd and Sm oxide content. That indicates the amorphous nature of the samples. The glass density tendency increase with the increase of Sm2O3 content as shown in Figure 2. It's due to the structural atom arrangement change when Sm2O3 substitute Nd2O3 in the Li2O-B2O3 glass network, 213 and the density of Sm2O3 (8.347 g/cm 3 ) greater than the density of Nd2O3 (7.24 g/cm 3 ). The excess density of the samples is due to the molecular weight of the samarium higher than any other component in the glass samples. Figure 2. The relation between the density and samarium oxide content Figure 3 shows the DTA curves obtained for Sm2O3-Nd2O3 doped lithium borate glass. This figure indicates the presence of endothermic peak Tg (glass transition temperature), the exothermic peak Tc (the crystallization temperature) and the endothermic peak Tm (melting temperature) which tabulated in Table 2. The Tg represents the strength or rigidity of the glassy structure [27]. The difference (△x) among Tx and Tg which employ the glass forming ability [28]. According to DTA curves, the values of x calculated. The impact substitution of Nd with Sm on the glass-forming ability can appear. From Table 2, observed that the quantity of x of all samples > 100, it means that all glass samples have glass-forming ability and thermal stability. Figure 4 shows the FTIR spectra of glasses doped with Nd 3+ and Sm 3+ ion with different concentrations. Three areas defined the borate glass transmission spectra, the band (1200 -1600 cm -1 ) is the primary region, the second region from 800 to 1200 cm -1 and the last from 600 to 800 cm -1 .

RESULTS AND DISCUSSION
Where the primary bands are the stretching, relaxation of the B-O bond of trigonal BO3 units, the second attributed to BO4units, and the third due to the bending vibrations of B-O-B linkages inside the borate network [29][30][31]. The rare earth oxides doped borate glass outcomes within the conversion of BO3  Figure 5 shows the Vis-NIR absorption spectrum acquired from the lithium borate glasses doped Nd 3+ and Sm 3+ with different concentrations. Figure 5 shows eight electronic f -f transition bands of Nd 3+ in Table 3. This result compared with the prior referenced recommendations [32]. Figure 6 shows the optical absorption spectra of the lithium borate glass doped with 1 mol % Sm2O3 or Nd2O3. The observed absorption bands assigned to appropriate fitting electronic f-f transitions inside Sm 3+ ion as shown in Table 4.   Figure 6. The optical absorption spectra of the lithium borate glass doped with 1 mol % Sm2O3 or Nd2O3     Table 5 shows the calculated (fcal), experimental (fexp) oscillator strengths of the glass system containing Sm 3+ and RMS deviation. The oscillating strengths of the various transformations (experimental and theoretical) calculated, and therefore the parameters of the Judd-Ofelt are calculated [33,34]. The RMS deviation calculated using the following relation [35][36][37].
N is the total number of energy levels. Table 6 shows the measured fexp , theoretical fcal oscillator strength of the glass system containing Nd 3+ and RMS deviation . From table 6, the value of is very low (< 1) which indicates the J-O theory is valid [38,39]. The values of RMS imply the good fitting relating to the measured fexp and the theoretical fcal oscillator strengths. This sample shows a slight difference between experiment fexp and calculation fcal. Three Judd-Ofelt parameters of Sm 3+ and Nd 3+ doped glass samples obtained, Ω2 parameter describes the environment asymmetric or Sm 3+ and O 2ligand covalence because the samarium ions found in the different coordination environment. Sometimes the samarium has the same coordination, however, there may a chance of change in the crystalline field due to the deviation in the samarium position.  These distortions may contribute effectively to covalent or asymmetric environments. The parameters Ω4 and Ω6 indicate the large properties of the glass such as hardness and viscosity. In current glass systems, J-O parameter values presented in Table 7, Table 8 and follow the tendency as Ω4> Ω 6> Ω2. The same trend observed in other glass systems [38][39][40][41]. According Jorgensen and Reisfeld [42], the Ωλ extra affected the crystal-field asymmetry and the changes in the energy distinction relating to 4fN and 4fN-15d configuration. In other phrases, Ω2 will increase because of the nephelauxetic impact. This occurs due to the deformation of the electronic orbital within the 4f configuration. Increase the overlap the 4f of Nd 3+ ion and oxygen orbital induced the energy level of Nd 3+ ion contracts and shifting inside the wavelength. Furthermore, shifting all transitions to higher wavelength indicate the presence of Nd -O linkages in the glass system. The transition 4 I9/2→ 2 G9/2 observed is greater intense than the alternative transitions which well see from the intensity of the calculated oscillator strength increases empirically and relates to the structural changes of the location of the rare-earth ions. Ω2 rose significantly by reducing the symmetry of the rare-earth site and the more covalent its chemical bond with the ligands field. As a whole, the Ω2 increases because of the covalence among the rare earth ion and the ligand field increases, as the symmetry lowers, and as the electric gradient relating the rare earth ion and the ligand fields increases. The higher the value of Ω4 in the current glass indicates the higher the hardness of the glass network and the higher covalent around the sm 3+ ions. The ratio between Ω4 to Ω6 indicates that all the samples containing Sm found this ratio greater than 1. These resulting analyses verify that the glass used as a laser generator. Figure 8 shows the variation of emission intensity for the transition of Sm 3+ -Nd 3+ containing glasses excited at 400 nm. It clears the three peaks at 561, 599 and 647 nm, which assigned to 4 G5/2→ 6 H5/2, 6 H7/2,  Figure 8. the emission spectra of Sm 3+ -Nd 3+ containing lithium borate glasses excited at 400 nm As it appears (in Figure 9) possible Nd 3+ ion energy 4 F3/2 level transfer to the Sm 3+ ion 6 F9/2 level. Thereby Sm 3+ ion excited 6 F9/2 to 4 G7/2 and subsequent de-excites to 4G5/2 via nonradiative decay and strengthens the emission transitions from Sm 3+ ions 4 G5/2. This increases the intensity of the Sm 3+ emission lines expenses the Nd 3+ emission lines. The branching ratio B value found highest the transition 4 G5/2 → 6 H7/2 (near orange emission) in the glasses and found that the value B for the transition 4 G5/2 → 6 H7/2 is 60, 57 and 51 % respectively. In many other glass systems, the highest B value of this transition reported from Sm 3+ ions. Finally the general analysis of the current results suggests that the combined interaction of the Sm 3+ ions containing Nd 3+ ions significantly improves the transfer of orange emissions from Sm 3+ ions into the studied glass system and makes the glasses suitable for orange emissions devices. Besides, the replacing 0.25 mole% Sm 3+ by Nd 3+ gives the highest intensity of the emitted radiation.

CONCLUSION
Samarium and neodymium ions doped Lithium borate glass prepared and studied. The density of glass samples indicates that the density measurement increases as samarium content increase and the distinction among the experimental and calculated density increase as the samarium content increase. The functional vibration groups within the glass matrix have studied and indicate the addition of rare earth ion transfer the BO3 vibration groups to BO4 and forming nonbridging oxygen. Judd-Ofelt (J-O) principle has applied and evaluates J-O intensity parameters. The general analysis of the results of the present study optical properties (absorption and emission) indicates that these glass samples are answerable for orange. Based on the results obtained from the J-O analysis, the parameters concluded that the glass under study is a promising luminescent and laser material. The current glasses in the study have the potential to act like an orange emission device as well as photovoltaic applications.