X-RAYS LUMINESCENCE, OPTICAL AND PHYSICAL STUDIES OF BI2O3-B2O3-SM2O3 GLASSES SYSTEM

Sm-doped bismuth borate glasses of the composition (5 0-x) SiO2: 50B2O3: xSm2O3 (where x = 0.00, 0.50, 1.00, 1.50, 2.00 and 2.50 mol%) have been synthesiz ed by conventional melt quenching technique. In ord er to understand the role of Sm 2O3 in bismuth borate glasses, the density, molar volu me, refractive index and optical absorption were investigated. The results s how that density, molar volume and refractive index of glasses increased with increasing Sm 2O3 concentration. The increase of molar volume with S m2O3 concentration is due to the increase of Non-Bridgin g Oxygen (NBOs) in the glass matrix. The optical absorption spectra were measured in the wavelength range from 300-1100 nm and the optical band gaps were determined. It was found that the optical band gap decreased with the increase of Sm 2O3 concentration. Moreover, the x-rays luminescence of Sm2O3 glasses samples were measured and shows emission band at G5/2→ H5/2 (569 nm), G5/2→ H (598 nm), G5/2→ H9/2 (641 nm) and G5/2→ H11/2 (705 nm). This investigation have been used as the basis for developing optical amplifier or glass scintill ator.


INTRODUCTION
Boric oxide, B 2 O 3 , acts as one of the most important glass formers and flux materials. Melts with compositions rich in B 2 O 3 exhibit rather high viscosity and tend to the formation of glasses. In crystalline form, on the other hand, borates with various compositions are of exceptional importance due to their interesting linear and nonlinear optical properties (Becker, 1998). The boron atom usually coordinates with either three or four oxygen atoms forming [BO 3 ] 3or [BO 4 ] 5structural units. Furthermore, these two fundamental units can be arbitrarily combined to form different B x O y structural groups (Xue et al., 2000). Among these borates, especially the monoclinic bismuth borate BiB 3 O 6 shows up remarkably large linear and nonlinear optical coefficients (Hellwig et al., 1999;. Calculations indicate that this can be mainly attributed to the contribution of the [BiO 4 ] 5anionic group (Xue et al., 1999;Lin et al., 2001). For the linear properties (refractive index) this anionic group should act in a similar way in an amorphous environment, i.e., in glass. Combining bismuth oxide with boric oxide thus allows tuning the optical properties in a wide range depending on the composition. Consequently, the properties of glasses of Science Publications PI the system Bi 2 O 3 -B 2 O 3 have attracted much interest (Becker, 2003). The trivalent samarium ion (Sm 3+ ) is one of the most important active ions in the RE family (cerium to lutetium) due to its convenient closely lying energy level structure (Carnall et al., 1968), that has been exploited in upconversion processes mainly in low phonon crystalline hosts and rarely in glasses (Kaczkan et al., 2001;Zhou et al., 2003;Biju et al., 2004;Farries et al., 1988;France et al., 2000). Hence very little is known about upconversion properties of Sm 3+ in glasses. Within the Sm 3+ ion energy scheme tricolor visible upconversion processes can take place from the 4 G 5/2 → 6 H 5/2 (green), 4 G 5/2 → 6 H 7/2 (orange) and 4 G 5/2 → 6 H 9/2 (red) electronic transitions. Moreover, Sm 3+ doped bismuth-borate glass has high density and radiation hard property. Also it is easy to made, can be produced with low cost and wide range of emission band. Therefore, it is a good candidate for radiation detector and possible to apply high energy and nuclear physics, medical imaging, homeland security and radiation detection. In this study, Sm 3+doped bismuth borate glasses have been synthesized by conventional melt quenching technique and investigate on x-rays luminescence, optical and physical properties of glass samples.

Experimental
The compositions of glass are (50-x) Bi 2 O 3 : 50B 2 O 3 : xSm 2 O 3 (x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 mol%). The batch was prepared from the AR grade of Bi 2 O 3 (Fluka 99.99%), H 3 BO 3 (Sigma-Aldrich, 99.99%) and Sm 2 O 3 (Sigma-Aldrich, 99.99%). The glasses were melted in a high alumina crucible at 1,100°C in air atmosphere. The molten glass was cast into a stainless steel plate and properly annealed. The glass thus obtained was cut and polished for optical measurement. The density was measured by the Archimedes method using xylene as immersion liquid. Density of xylene at the experimental temperature was found to be 0.863 g/cm 3 . The corresponding molar volume, V m , was calculated using the following Equation (1) (Limkitjaroenporn et al., 2011): where, M is the molecular weight of the multicomponent glass system.
The UV-Vis absorption spectra were obtained with a double-beam spectrophotometer (Variance, Cary-50). According to Davis and Mott, the absorption coefficient, α(v), as a function of incident photon energy (hv) for direct and indirect optical transitions is given by (Abdel-Baki et al., 2006): where the exponent n = 1/2 for an allowed direct transition, while n = 2 for an allowed indirect transition, α 0 is a constant related to the extent of the band tailing and E g is the optical band gap energy. The absorption coefficient, α(v), can be determined near the absorption edge of different photon energies for all glass sample. It is well known that for amorphous materials a reasonable fit of Equation (2) with n = 2 is achieved. Therefore, the values of optical band gap energy (E g ) can be determined from the plot of (αhv) 1/2 versus photon energy (hv) (Tauc's plot), for allowed indirect transitions. Refractive index of these glasses has been calculated by using the relation proposed by (Dimitrov and Komatsu, 2002;Eraiah and Bhat, 2007) In order to measure the x-ray luminescence of the Sm 2 O 3 doped bismuth borate glass samples at room temperature, x-ray tube (DRGEM Co.) was used and faces of the glass sample were wrapped with several layers of Teflon tape excepting the one for attaching to the optical fiber. Signals from the glass sample by the induced x-ray were measured using a QE65000 spectrometer (Ocean Optics Co.) The QE65000 was cooled to-15 to reduce thermal noise in the CCD. It was used to plot the x-ray emission spectrum of the glass sample by window based-software (Kim et al., 2011;Rooh et al., 2009).

Density and Molar Volume
The measured density of Sm 3+ doped bismuth borate glass samples for different Sm 2 O 3 concentrations are shown in Fig. 1. As seen in Fig. 1, density increase linearly with additional content of Sm 2 O 3 into the network. Figure 2 shows the variation of the molar volume with Sm 2 O 3 concentration. As Science Publications PI shown in Fig. 2, the molar volume increases with an increase in Sm 2 O 3 content.

Optical Spectra, Optical Band Gap and Refractive Index
The absorption spectra of Sm 3+ doped bismuth borate glasses in the UV-VIS region at room temperature are shown in Fig. 3. It is clearly observed that the absorption intensity of the absorption bands increases with the increase of Sm 2 O 3 concentration. Three absorption bands peaked at 474 nm, 950 nm and 1083 nm were observed. From absorption spectra, the optical band gap were evaluated by Tauc's plot using Equation (2) and shown in Fig. 4. the results shows that the optical bandgap decreased with increasing of Sm 2 O 3 concentration (Fig. 5). Refractive index of these glasses has been calculated by using Equation 3 and show in Fig. 6. The result show refractive index of glasses increased with increasing of Sm 2 O 3 concentration.

X-Rays Luminescence
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Density and Molar Volume
From the increasing of density results, indicates that replacing B 2 O 3 by addition of Sm 2 O 3 is effects to increase of the average molecular weight due to Sm 2 O 3 has a higher relative molecular weight than that of B 2 O 3 . As shown in Fig. 2, the molar volume increases with an increase in Sm 2 O 3 content, which is attributed to the increase in the number of Non-Bridging Oxygen (NBOs). The increase of NBOs in the structure generally leads to an increase in average atomic separation. The results obtained indicate that the samarium oxide enters the glass network as a modifier by occupying the interstitial space in the network and generating the NBOs to the structure. It can also be concluded that the addition of Sm 2 O 3 may accordingly result in an extension of glass network (Sindhu et al., 2005).

Optical Spectra, Optical Band Gap and Refractive Index
All absorption band spectra are characteristics of Sm 3+ -doped oxide glasses (Som and Karmakar, 2008) and the observed absorption bands were assigned to appropriate f-f electronic transitions of Sm 3+ ions from the 6 H 5/2 ground state to ( 4 I 13/2 + 4 I 11/2 + 4 M 15/2 ), 6 F 11/2 and 6 F 9/2 respectively. From optical band gap result show that, when increase Sm 2 O 3 , bonding defect and non-bridging oxygen were increased. These leads to increase in the degree of localization of electrons there by increasing the donor center in the glass matrix. The increasing presence of donor center, therefore, decreases the optical band gap. As a result of this, band gap are decreased as shown in Fig. 5, for indirect allow transition. For this case the refractive index of glasses were increased. This result is effects from increasing of density and polarizability of Sm 3+ doped bismuth borate glass.

CONCLUSION
In this study, Sm 3+ -doped bismuth borate glasses of the composition (50-x) SiO 2 : 50B 2 O 3 : xSm 2 O 3 (where x = 0.00, 0.50, 1.00, 1.50, 2.00 and 2.50 mol%) have been synthesized by conventional melt quenching technique The results show that density, molar volume and refractive index of glasses increased with increasing Sm 2 O 3 concentration. The increase of molar volume with Sm 2 O 3 concentration is due to the increase of Non-Bridging Oxygen (NBOs) in the glass matrix. It can also be concluded that the addition of Sm 2 O 3 may accordingly result in an extension of glass network. The optical absorption spectra were measured in the wavelength range from 300-1100 nm and three absorption bands peaked at