Spectroscopic Studies of 50 Bi 2 O 3-( 50 − x ) B 2 O 3x Sm 2 O 3 Glasses System

Sm doped bismuth borate glasses of the composition (50 − x)B2O3:50Bi2O3:xSm2O3 (where x = 0.00, 0.50, 1.00, 1.50, 2.00 and 2.50 mol%) have been synthesized by conventional melt quenching technique. In order to understand the role of Sm2O3 in bismuth borate glasses, the density, the molar volume, the refractive index and the optical absorption were investigated. The results show that density, molar volume and refractive index of glasses increased with increasing Sm2O3 concentration. The increase of molar volume with Sm2O3 concentration is due to increase of non-bridging oxygen (NBOs) in the glass matrices. The optical absorption spectra were measured in the wavelength range 300 1100 nm and the optical band gaps were determined. It was found that the optical band gap decreased with the increase of Sm2O3 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→H7/2 (598 nm), G5/2→H9/2 (641 nm) and G5/2→H11/2 (705 nm).


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 [1].The boron atom usually coordinates with either three or four oxygen atoms forming (BO 3 ) 3− or (BO 4 ) 5− structural units.Furthermore, these two fundamental units can be arbitrarily combined to form different B x O y structural groups [2].Among these borates, especially the monoclinic bismuth borate BiB 3 O 6 shows up remarkably large linear and nonlinear optical coefficients [3,4].Calculations indicate that this can be mainly attributed to the contribution of the (BiO 4 ) 5− anionic group [5,6].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 the system Bi 2 O 3 -B 2 O 3 have attracted much interest [7].
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 [8], that has been exploited in upconversion processes mainly in low phonon crystalline hosts and rarely in glasses [9][10][11][12][13].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 work, 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) B 2 O 3 :50Bi 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 , H 3 BO 3 and Sm 2 O 3 .The glasses were melted in a high alumina crucible at 1100˚C under normal 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 formula [14]: where M is the molecular weight of the multi-component 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, (), as a function of incident photon energy (h) for direct and indirect optical transitions is given by [15]: where the exponent n = 1/2 for an allowed direct transition, while n = 2 for an allowed indirect transition,  0 is a constant related to the extent of the band tailing, and E g is the optical band gap energy.The absorption coefficient, (), 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 (h) 1/2 versus photon energy (h) (Tauc's plot), for allowed indirect transitions.Refractive index of these glasses has been calculated by using the relation proposed by Dimitrov et al. [16,17].
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 QE65,000 spectrometer (Ocean Optics Co.) The QE65,000 was cooled to −15˚C 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 [18,19].

Result and Discussion
The template is used to format your paper and style the text.All margins, column widths, line spaces, and text fonts are prescribed; please do not alter them.You may note peculiarities.For example, the head margin in this template measures proportionately more than is customary.This measurement and others are deliberate, using specifications that anticipate your paper as one part of the entire proceedings, and not as an independent document.Please do not revise any of the current designations.The measured density of Sm 3+ doped bismuth borate glass samples for different Sm 2 O 3 concentrations are shown in The optical band gap were evaluated by Tauc's plot using Equation (2) and shown in Figure 4.When increase Sm 2 O 3 , bonding defect and non-bridging oxygen were increased.These leads to increase in the degree of   Figure 7 showed X-rays luminescence spectra of Sm 2 O 3 doped bismuth borate glasses.The emission wavelength observed at 569 nm, 598 nm, 641 nm and 705 nm The luminescence spectra of the Sm 2 O 3 doped bismuth borate glass were identified as 4 G 5/2 → 6 H 5/2 (569 nm), 4 G 5/2 → 6 H 7/2 (598 nm), 4 G 5/2 → 6 H 9/2 (641 nm) and 4 G 5/2 → 6 H 11/2 (705 nm) [22].The intensity of luminescence was increase with increasing doping concentration.
1) The density increase linearly with additional content  of Sm 2 O 3 into the network, due to Sm 2 O 3 has a higher relative molecular weight than that of B 2 O 3 .
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).
4) When increase Sm 2 O 3 , bonding defect and nonbridging 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 and increases refractive index.

Figure 1 .
As seen in Figure 1, density increase linearly with additional content of Sm 2 O 3 into the network.This indicates that replacing B 2 O 3 by addition of a small amount of Sm 2 O 3 results in the 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 .Figure 2 shows the variation of the molar volume with Sm 2 O 3 concentration.As shown in Figure 2, the molar volume increased with an increasing of Sm 2 O 3 concentration, because of increasing of non-bridging oxygen (NBOs).The increase of NBOs in the glass structure leads to an increase in average atomic separation.The results obtained indicate that the Sm 2 O 3 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 [20].The absorption spectra of Sm 3+ doped bismuth borate glasses in the UV-VIS region at room temperature are shown in Figure 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.All absorption band spectra are characteristics of Sm 3+ doped oxide glasses [21] 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.

6 .
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, the band gap are decreased as shown in Figure 5, for indirect allow transition.The refractive index of these glasses has been calculated by using Equation (3) and show in Figure The result show the refractive index of glasses increased with increasing of Sm 2 O 3 concentration.

Figure 5 .Figure 6 .
Figure 5. Variation of optical band gap (for indirect allow transition) with Sm 2 O 3 concentration.