Pr3+ doped zinc fluoroborate glasses with the chemical composition [(mol %) 30ZnF2 – 20 TeO2 – (50-x) B2O3 – xPr6O11] (where x = 0.0, 0.1, 0.5, 1.0 and 1.5 mol %) of different concentration of rare earth element praseodymium (Pr3+) have been prepared by conventional melt quench technique. The physical parameters like density, refractive index, number density, molar refraction, molar electronic polarizability, electronic polarizability, dielectric constant, polaron radius, inter–ionic separation, molar volume and oscillator strength of these glasses were calculated as a function of dopant concentration. The densities and refractive indices of these glasses were found to be in the range 2.0 g/cm3 - 2.67 g/cm3 and 1.644 – 1.73 respectively. Stability of the glass doped with 1.0 mol % Pr3+ was found to be 120

Kamath, Sudha D

PrajnaShree, M

Raviprakash, Y

Sangeetha, B.

Wagh, Akshatha

English

European Scientific Journal (European Scientific Institute)

European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  83  CHARACTERIZATION OF Pr6O11 DOPED ZINC FLUOROBORATE GLASS    PrajnaShree M Akshatha Wagh Raviprakash Y Department of Physics, Manipal Institute of Technology, Manipal Sangeetha B. Department of Chemistry, Manipal Institute of Technology, Manipal Sudha D Kamath Department of Physics, Manipal Institute of Technology, Manipal   Abstract Pr3+ doped zinc fluoroborate glasses with the chemical composition [(mol %) 30ZnF2 – 20 TeO2 – (50-x) B2O3 – xPr6O11] (where x = 0.0, 0.1, 0.5, 1.0 and 1.5 mol %) of different concentration of rare earth element praseodymium  (Pr3+) have been prepared by conventional melt quench technique. The physical parameters like density, refractive index, number density, molar refraction, molar electronic polarizability, electronic polarizability, dielectric constant, polaron radius, inter–ionic separation, molar volume and oscillator strength of these glasses were calculated as a function of dopant concentration. The densities and refractive indices of these glasses were found to be in the range 2.0 g/cm3 - 2.67 g/cm3 and 1.644 – 1.73 respectively. Stability of the  glass doped with 1.0 mol % Pr3+  was found to be 120.  Keywords: Praseodymium doped glasses, oscillator strength, optical energy gap, absorption spectrum, electronic polarizability  Introduction  Glass doped with various rare earth ions are attracting attention since they are seen as promising materials for high power lasers. The properties of doped glasses depend on the concentration of the dopant ions as well as the chemical environment of the host material. Glasses with different host material doped with ions in different proportion are therefore being developed and their suitability as laser material is tested by measurement of their optical properties. Incorporated in glassy matrices, the rare earth European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  84  element praseodymium (Pr3+) shows efficient luminescence only when it is in its triply ionized state. The observed electric dipole transitions of Pr3+ involve primarily the excited states 3Pj (j=0,1,2) and 1D2 and the ground state 3H4 or the other low lying states of the 4f2 configuration. Compared to the intraconfigurational (4fn) optical transitions of the other rare earth ions, the electric dipole transition 3P1        3H4  of Pr3+ exhibits a shorter decay time.  In many technical applications scintillators with fast luminescence decay are required, and Pr3+ is used as a dopant in the X– ray conversion detectors used for modern X- ray computer tomography experiments. Transitions from the 3P0, 1, 2 levels of Pr3+ are also used in phosphors. The other prominent transition of Pr3+ is 1D2 .         3H4 which has a much longer decay time and lasing has been observed for this transition. The optical properties of Pr3+ in various glass hosts are, however, still not as thoroughly investigated, as for the other rare earth ions due to difficulties in the preparation of these glasses. In the present paper, we report physical as well as optical properties of Pr3+ doped zinc fluoride glass (Mahato,1999). Material and Methods  The chemical composition used to develop Pr3+ doped zinc fluoride glasses is 30 ZnF2 – 20 TeO2 – (50 – x) B2O3 – x Pr6O11  Where x = 0, 0.1, 0.5, 1.0 and 1.5 mol % of Pr6O11. All the ingredients with a reported purity of 99.99% were used, imported from Sigma Aldrich. A mixture of these compounds was powdered in a ceramic mortar and was made a homogeneous mixture. This mixture was taken in a ceramic boat and heated in Muffle furnace up to 1000 ◦C for 2 hours. Then the melt was poured onto a metal plate and pressed with another metal plate which resulted into a transparent glass (Mahato,1999). Results and Discussion Physical Properties  Fig.1: The variation of (a) density (b) refractive index of the glass samples with a change in the Pr6O11 concentration. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  85  Density is an effective tool to explore the degree of structural compactness modification of the geometrical configurations of the glass network. The density, ρ, of the glass samples were measured at room temperature (300 K) according to Archimedes Method using distilled water as the immersion liquid using Sartorius BSA series electronic analytical and precision balance. The density of distilled water at the experimental temperature was taken to be 0.999 g/cm3. The density of glass was calculated according to the formula:                                              ρ = [WA / (WA – WB)] * 0.999 Where WA is the weight of the sample in air and WB is the weight of the sample in distilled water (Eraiah, 2006). Plot of density versus different concentration of Pr3+ doped in glass matrix is shown in Fig.1 (a). Refractive index is one of the most important properties in optical glasses. Therefore, a large number of researchers have carried out investigations to ascertain the relation between refractive index and glass composition. Refractive Index, n, of each sample was measured using the portable jewel Refractometer at single line sodium wavelength of 589.3 nm and sensitivity of 0.01. Plot of refractive index versus different concentration of  Pr3+ doped  in glass matrix is shown in Fig.1 (b). The number density of rare – earth ions (N) were determined using the formula given in equation. Thus the number density (N) of Pr3+ ions can be calculated by N = [(ρ / M total) * MC * 2 * Av] where ρ is the glass density, MC is the molar percent concentration of rare – earth element, Mtotal is the sum of molecular weights in rare- earth borate glass and Av is Avogadro’s number [Av = 6.022 * 1023] (Hai Lin,2005).  The molar refraction, (Rm) of the glass samples were calculated using the formula which is well known as Volf and Lorentz - Lorenz formula, Rm = {[(n2 – 1)/ (n2 + 2)] * [M/ ρ]  Where n is the refractive index of the glass sample, ρ is the density and M is the molecular weight of the glass samples. M / ρ is called the molar volume, (Vm)  The molar refraction is related to the structure of the glass and it is proportion to the molar electronic polarizability of the material (αm) according to the relation, (Kaewwiset, 2009).   αm = [3 / (4* π * Av)] * Rm  The reflection loss from the glass surface was computed from the refractive index using Fresnel’s formula,                                                     R = [(n2 – 1 ) / ( n2 + 2 )]  Where n is the refractive index. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  86   The dielectric constant (ε) was calculated using refractive index of the glass, ε = n2  Where n is the refractive index.  The electronic polarizability (αe) was calculated using the formula,                                                      αe = [3 * (n2 - 1) / [4 * π (n2  + 2) ]   Where N is the number of praseodymium ions per unit volume and n is the refractive index.  The polaron radius ( rp ) was calculated using the formula,                                                     rp=  (1/2) *[ (π / (6 * N))](1/3) Where N is the number of praseodymium ions per unit volume.  The inter – ionic separation (ri) was calculated using the formula                                                     ri = [ 1𝑁 ](1/3)  Where N is the number of praseodymium ions per unit volume (Raghavendra, 2011).    Based on the determined density and refractive index, the various physical properties of the glass studied are present in Table 1.  Table 1: The physical property of Pr6O11 doped zinc fluoroborate glass. Physical Properties Glass Code P1 P2 P3 P4 P5 Concentration of Pr6O11 (mol %)  0 0.1 0.5 1.0 1.5 Molecular Weight (M) (g /mol)    4.88 4.92  5.11  5.35  5.58  Density (ρ) (g/cm3)    2.0    2.67    2.24    2.6        2.2 Refractive Index  (n)    1.644    1.73    1.683    1.7        1.681 Number Density (N) *1022/cm3)    0   6.536   5.279   0.585     0.712 Molar Refraction (Rm) (cm3/mol)    0.883    0.735    0.865    0.795 0.959 Molar Electronic Polariability (αm) (*1024/ cm3)  -   2.686    3.911  32.438       32.15 European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  87  Electronic Polrizability (αe)  (*1024 ions / cm3)  -    2.452    2.588 15.764       12.68 Dielectric Constant (ε)  2.702    2.992   2.832   2.89        2.825 Reflection Loss  0.362    0.399   0.379   0.386        0.378 Inter-Ionic Distance (ri) (Ao)  - 0.0248   0.0266   0.0119 0.0111 Polaron Radius (rp) (Ao) -    0.01   0.01   0.4817 0.4512 The corresponding molar volume (Vm) was calculated using the relation,  Vm = MT / ρ,  Where MT is the total molecular weight of the multi-component glass system by  MT = xTeO2 ZTeO2 + xB2O3 ZB2O3 + xPr6O11 ZPr6O11  Where,  xTeO2 ,xB2O3 and xPr6O11 =  the mole fractions of the constituents oxides.               ZTeO2 , ZB2O3 and ZPr6O11 =  the molecular weights of the constituents oxides.  Using this formula molar volume for glass doped with 1.0 mol % concentration was calculated. Table 2 determines molar volume with different Pr6O11 concentration (% mol). Table 2: Variation of molar volume with different concentration. Concentration ( mol % ) Molar Volume ( cm3, mol -3 ) 0.0 33.365 0.1 25.348 0.5                    31.91 1.0                    29.323 1.5                    36.818            European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  88    Fig. 2 illustrates molar volume as the function of Pr6O11 concentration (% mol).  The behaviour of molar volume mainly depends upon the density of glasses (Eraiah, 2006). Fig. 2: Molar volume of [30 ZnF2 – 20 TeO2 – (50 – x ) B2O3 – x Pr6O11]  glass system. Optical Properties Absorption Spectrum Optical absorption in solids occurs by various mechanisms, in all of which the photon energy will be absorbed by either the lattice or by electrons where the transferred energy is covered. The lattice (or phonon) absorption will give information about atomic vibrations involved and this absorption of radiation normally occurs in the UV-Visible region of the spectrum. Optical absorption is a useful method for investigating optically induced transitions and for getting information about the band structure and energy gap of non-crystalline materials. The principle of this technique is that a photon with energy greater than the band gap energy will be absorbed. To study the optical properties like optical energy gap, oscillator strengths of different transitions possible in praseodymium doped glasses, we recorded absorption spectra of these glasses using an Ocean Optics CHEMUSB4-UV-VIS single beam spectrophotometer shown in Fig.3. The CHEMUSB4-UV-VIS consists of a USB4000 Spectrometer with a combination of deuterium tungsten halogen light source and 1 cm cuvette holder with high-speed electronics. The spectrophotometer covers 210 to 880 nm range, has optical resolution of 1.0 nm (FWHM) and captures 3648 wavelengths in less than 1 second. It sees changes as small as 0.01 Absorbance Units. The light source (far right) sends light via an input fiber into a cuvette in a cuvette holder (bottom center). The light interacts with the sample. The output fiber carries light from the sample to the spectrometer (top center) connected to the computer (far left).              European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  89   Fig.3: Ocean Optics CHEMUSB4-UV-VIS single beam spectrophotometer used for recording absorbance spectra of Pr6O11 doped zinc fluoroborate glasses.  The absorption spectrums of the glasses were recorded in a Ocean Optics USB4000-UV-VIS single beam spectrometer in both the UV and visible spectral region ranging from 200 nm to 700 nm. The spectra’s were obtained using software called Spectra Suite. Absorption spectra of zinc fluoroborate glasses recorded at temperature 300 K with 1.0 mol % Pr6O11 concentration are shown in Fig.4. The high phonon energy in borate glass is not detrimental to Sm3+ and Pr3+ normal 4f transition emissions, and sometimes it can accelerate the relaxation processes, which is necessary and beneficial for visible emissions. The absorption spectrum in visible region of 1.0 mol% of Pr6O11 doped borate glass demonstrates the suitability of borate glasses as a suitable host for Pr3+ .                                      Fig. 4 : Absorption spectrum of zinc fluoride glass doped with 1.0 mol % doped Pr3+.   The observed electric dipole transitions of Pr3+ involve primarily the excited states 3Pj (j=0, 1, 2) and 1D2 (Sharma, 2005).  Oscillator Strength  The assignment of the lines, their frequencies and the spectral oscillator strength (f x 10-6) are given in Table 3.The oscillator strength (f) corresponding to the different transitions was obtained by integrating the intensities of the absorption bands. It is given as 𝑓 =  𝑚𝑐2𝜋𝑁𝑒2�𝛼(𝛾|)𝑑𝛾|          𝑤ℎ𝑒𝑟𝑒  𝛼(𝛾)��� = ln �𝐼0(?̅?)𝐼(?̅?) �𝑡= 2.303 𝐸(𝛾)���/𝑡 where  m is the mass of electron, N is the number of rare earth ions, c is the speed of light, ?̅? is the wavenumber, 𝛼 (𝛾)���  is the absorbance, and t is the sample thickness. The oscillator strength is thus obtained (Hai Lin, 2005).    European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  90     Table 3: The assignment of the lines, their frequencies and the spectral oscillator strength (f X10-6) are given in table.  Wavelength (nm)  Energy  (cm-1)  Assignment  Oscillator Strength (*10-6) 438 22831.05 3P2 7.67 464 21551.72 3P1 3.99 476 21008.40 3P0 2.31 584 17123.28 1D2 9.13 The points shown in the Table 3 are specified in Fig.4 and we have found that the peak at wavelength 584 nm have maximum oscillator strength. This means that, the 1D2 transition has higher energy and this can be used to build lasers. Optical Band Energy Gap:  The experimental value of the absorption coefficient  () is calculated by using the equation, α (ω) = ( 2.303 * A ) / d  Theoretically, the optical band gap energy for indirect allowed optical transitions can be calculated. The quantity ( f)1/2 is plotted as a function of the photon energy (ђf) for glass sample doped with 1.0 mol % is as shown in the Fig.5. The straight portion of the graph is then extrapolated to intersect with x axis. The value of ђf at the point where ( f)1/2 becomes zero yields a direct measure of the optical band gap energy (Altaf,2005). The optical band gap energy was found to be 2.83eV.  Fig.5: A representative plot of the quantity (αђf) ½ as a function of the photon energy            (ђf). Glass Stability  The stability of the glass was measured by using Differential Scanning Calorimeter (DSC). Here glass stability was calculated by taking the difference of crystalline temperature (Tc) and glass transition temperature (Tg). Higher the value, higher is the glass stability. The stability of the glass doped with 1.0 mol % was found to be 120 and for undoped glass it is 50. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  91   Fig.6: DSC plots of 1.0 mol % Pr3+ doped zinc fluoride glass.  Conclusion  In the present study, the glass samples of composition [30 ZnF2 – 20 TeO2 – (50 – x ) B2O3 – x Pr6O11]  (where, x = 0.0, 0.1, 0.5, 1.0 and 1.5 mol %)  have been synthesized by normal melt-quench technique. The density and refractive index results show unusual behaviour with no particular trend in either increase or decrease of the outcomes. This might be because of the substitution of B2O3 oxides into Te2O3 where B2O3 plays a dual nature, it acts as network modifier and network former position for different concentrations of the dopant. The electronic polarizability for 1.0 mol% was found to be maximum compared to other glass samples [Table 1]. Stability of the 1.0 mol % doped glass was measured to be 120. The energy band gap of the doped glass mentioned above was found to be 2.83 eV. The absorption spectrum, gave the strength of 1D2  line to be maximum. In the present work, the glasses with more than 30% of zinc have been built which finds its applications in both photonics and optoelectronics fields.   References: Mahato, K. K.,  Rai,D.K.,1999, Optical Studies of  Pr3+ Doped Oxyfluoroborate  Glass, Phys. Stat. Sol.(a) 174, 277 – 289. Eraiah, B., 2006, Optical Properties of Samarium Doped Zinc – Tellurite Glasses, Bull. Mater. Sci., Vol 29, No. 4, 375-378.  Lin,H., Yang,D., Liu, G., Tiecheng, M., Bin, Z., Qingda, A., Jiayou,  Y., Xiaojun, W., Xingren, L., Edwin, Y., 2005, Optical Absorption and   Photoluminescence in Sm3+ and Eu3+ Doped Rare Earth Borate Glasses, Journal of  Luminescence,113,121–128. Weeranut, K., Jakrapong, K., Pichet, L., 2009, UV – VISIBLE – NIR Study Of Er3+ Doped Soda Lime Silicate Glass, International  Conference on the Role of Universities in Hands – On Education Rajamangala University of Technology Lanna, Chiang – Mai, Thailand.. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  92  Raghavendra, R., Rama, K., Udayachandran, T., Venkata, R., Reddy, Y.P., Sambasiva, R., Ravikumar, S.N., 2011, Effect of Li2O Content on Physical and Structural Properties of Vanadyl Doped Alkali Zinc Borate Glasses”, Physica B, 406, 2132 – 2137. Sharma, Y.K., Dubedi, R.P., Joshi, V., Karnataka K.B., Surana, S.S.L., 2005, Absorption Studies of Tripositive Praseodymium and Neodymium Doped Zinc Fluoride BoroPhosphate Glasses, Indian Journal of Engineering and Material Science,12, 65-74.  Altaf, M., Chaudhry, M.A., Siddiqi.S.A., 2005, Glass, Physics and Chemistry, Vol. 31, No. 5, 597-601.                                 

CHARACTERIZATION OF Pr6O11 DOPED ZINC FLUOROBORATE GLASS

European Scientific Journal, ESJ

European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  83  CHARACTERIZATION OF Pr6O11 DOPED ZINC FLUOROBORATE GLASS    PrajnaShree M Akshatha Wagh Raviprakash Y Department of Physics, Manipal Institute of Technology, Manipal Sangeetha B. Department of Chemistry, Manipal Institute of Technology, Manipal Sudha D Kamath Department of Physics, Manipal Institute of Technology, Manipal   Abstract Pr3+ doped zinc fluoroborate glasses with the chemical composition [(mol %) 30ZnF2 – 20 TeO2 – (50-x) B2O3 – xPr6O11] (where x = 0.0, 0.1, 0.5, 1.0 and 1.5 mol %) of different concentration of rare earth element praseodymium  (Pr3+) have been prepared by conventional melt quench technique. The physical parameters like density, refractive index, number density, molar refraction, molar electronic polarizability, electronic polarizability, dielectric constant, polaron radius, inter–ionic separation, molar volume and oscillator strength of these glasses were calculated as a function of dopant concentration. The densities and refractive indices of these glasses were found to be in the range 2.0 g/cm3 - 2.67 g/cm3 and 1.644 – 1.73 respectively. Stability of the  glass doped with 1.0 mol % Pr3+  was found to be 120.  Keywords: Praseodymium doped glasses, oscillator strength, optical energy gap, absorption spectrum, electronic polarizability  Introduction  Glass doped with various rare earth ions are attracting attention since they are seen as promising materials for high power lasers. The properties of doped glasses depend on the concentration of the dopant ions as well as the chemical environment of the host material. Glasses with different host material doped with ions in different proportion are therefore being developed and their suitability as laser material is tested by measurement of their optical properties. Incorporated in glassy matrices, the rare earth European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  84  element praseodymium (Pr3+) shows efficient luminescence only when it is in its triply ionized state. The observed electric dipole transitions of Pr3+ involve primarily the excited states 3Pj (j=0,1,2) and 1D2 and the ground state 3H4 or the other low lying states of the 4f2 configuration. Compared to the intraconfigurational (4fn) optical transitions of the other rare earth ions, the electric dipole transition 3P1        3H4  of Pr3+ exhibits a shorter decay time.  In many technical applications scintillators with fast luminescence decay are required, and Pr3+ is used as a dopant in the X– ray conversion detectors used for modern X- ray computer tomography experiments. Transitions from the 3P0, 1, 2 levels of Pr3+ are also used in phosphors. The other prominent transition of Pr3+ is 1D2 .         3H4 which has a much longer decay time and lasing has been observed for this transition. The optical properties of Pr3+ in various glass hosts are, however, still not as thoroughly investigated, as for the other rare earth ions due to difficulties in the preparation of these glasses. In the present paper, we report physical as well as optical properties of Pr3+ doped zinc fluoride glass (Mahato,1999). Material and Methods  The chemical composition used to develop Pr3+ doped zinc fluoride glasses is 30 ZnF2 – 20 TeO2 – (50 – x) B2O3 – x Pr6O11  Where x = 0, 0.1, 0.5, 1.0 and 1.5 mol % of Pr6O11. All the ingredients with a reported purity of 99.99% were used, imported from Sigma Aldrich. A mixture of these compounds was powdered in a ceramic mortar and was made a homogeneous mixture. This mixture was taken in a ceramic boat and heated in Muffle furnace up to 1000 ◦C for 2 hours. Then the melt was poured onto a metal plate and pressed with another metal plate which resulted into a transparent glass (Mahato,1999). Results and Discussion Physical Properties  Fig.1: The variation of (a) density (b) refractive index of the glass samples with a change in the Pr6O11 concentration. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  85  Density is an effective tool to explore the degree of structural compactness modification of the geometrical configurations of the glass network. The density, ρ, of the glass samples were measured at room temperature (300 K) according to Archimedes Method using distilled water as the immersion liquid using Sartorius BSA series electronic analytical and precision balance. The density of distilled water at the experimental temperature was taken to be 0.999 g/cm3. The density of glass was calculated according to the formula:                                              ρ = [WA / (WA – WB)] * 0.999 Where WA is the weight of the sample in air and WB is the weight of the sample in distilled water (Eraiah, 2006). Plot of density versus different concentration of Pr3+ doped in glass matrix is shown in Fig.1 (a). Refractive index is one of the most important properties in optical glasses. Therefore, a large number of researchers have carried out investigations to ascertain the relation between refractive index and glass composition. Refractive Index, n, of each sample was measured using the portable jewel Refractometer at single line sodium wavelength of 589.3 nm and sensitivity of 0.01. Plot of refractive index versus different concentration of  Pr3+ doped  in glass matrix is shown in Fig.1 (b). The number density of rare – earth ions (N) were determined using the formula given in equation. Thus the number density (N) of Pr3+ ions can be calculated by N = [(ρ / M total) * MC * 2 * Av] where ρ is the glass density, MC is the molar percent concentration of rare – earth element, Mtotal is the sum of molecular weights in rare- earth borate glass and Av is Avogadro’s number [Av = 6.022 * 1023] (Hai Lin,2005).  The molar refraction, (Rm) of the glass samples were calculated using the formula which is well known as Volf and Lorentz - Lorenz formula, Rm = {[(n2 – 1)/ (n2 + 2)] * [M/ ρ]  Where n is the refractive index of the glass sample, ρ is the density and M is the molecular weight of the glass samples. M / ρ is called the molar volume, (Vm)  The molar refraction is related to the structure of the glass and it is proportion to the molar electronic polarizability of the material (αm) according to the relation, (Kaewwiset, 2009).   αm = [3 / (4* π * Av)] * Rm  The reflection loss from the glass surface was computed from the refractive index using Fresnel’s formula,                                                     R = [(n2 – 1 ) / ( n2 + 2 )]  Where n is the refractive index. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  86   The dielectric constant (ε) was calculated using refractive index of the glass, ε = n2  Where n is the refractive index.  The electronic polarizability (αe) was calculated using the formula,                                                      αe = [3 * (n2 - 1) / [4 * π (n2  + 2) ]   Where N is the number of praseodymium ions per unit volume and n is the refractive index.  The polaron radius ( rp ) was calculated using the formula,                                                     rp=  (1/2) *[ (π / (6 * N))](1/3) Where N is the number of praseodymium ions per unit volume.  The inter – ionic separation (ri) was calculated using the formula                                                     ri = [ 1𝑁 ](1/3)  Where N is the number of praseodymium ions per unit volume (Raghavendra, 2011).    Based on the determined density and refractive index, the various physical properties of the glass studied are present in Table 1.  Table 1: The physical property of Pr6O11 doped zinc fluoroborate glass. Physical Properties Glass Code P1 P2 P3 P4 P5 Concentration of Pr6O11 (mol %)  0 0.1 0.5 1.0 1.5 Molecular Weight (M) (g /mol)    4.88 4.92  5.11  5.35  5.58  Density (ρ) (g/cm3)    2.0    2.67    2.24    2.6        2.2 Refractive Index  (n)    1.644    1.73    1.683    1.7        1.681 Number Density (N) *1022/cm3)    0   6.536   5.279   0.585     0.712 Molar Refraction (Rm) (cm3/mol)    0.883    0.735    0.865    0.795 0.959 Molar Electronic Polariability (αm) (*1024/ cm3)  -   2.686    3.911  32.438       32.15 European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  87  Electronic Polrizability (αe)  (*1024 ions / cm3)  -    2.452    2.588 15.764       12.68 Dielectric Constant (ε)  2.702    2.992   2.832   2.89        2.825 Reflection Loss  0.362    0.399   0.379   0.386        0.378 Inter-Ionic Distance (ri) (Ao)  - 0.0248   0.0266   0.0119 0.0111 Polaron Radius (rp) (Ao) -    0.01   0.01   0.4817 0.4512 The corresponding molar volume (Vm) was calculated using the relation,  Vm = MT / ρ,  Where MT is the total molecular weight of the multi-component glass system by  MT = xTeO2 ZTeO2 + xB2O3 ZB2O3 + xPr6O11 ZPr6O11  Where,  xTeO2 ,xB2O3 and xPr6O11 =  the mole fractions of the constituents oxides.               ZTeO2 , ZB2O3 and ZPr6O11 =  the molecular weights of the constituents oxides.  Using this formula molar volume for glass doped with 1.0 mol % concentration was calculated. Table 2 determines molar volume with different Pr6O11 concentration (% mol). Table 2: Variation of molar volume with different concentration. Concentration ( mol % ) Molar Volume ( cm3, mol -3 ) 0.0 33.365 0.1 25.348 0.5                    31.91 1.0                    29.323 1.5                    36.818            European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  88    Fig. 2 illustrates molar volume as the function of Pr6O11 concentration (% mol).  The behaviour of molar volume mainly depends upon the density of glasses (Eraiah, 2006). Fig. 2: Molar volume of [30 ZnF2 – 20 TeO2 – (50 – x ) B2O3 – x Pr6O11]  glass system. Optical Properties Absorption Spectrum Optical absorption in solids occurs by various mechanisms, in all of which the photon energy will be absorbed by either the lattice or by electrons where the transferred energy is covered. The lattice (or phonon) absorption will give information about atomic vibrations involved and this absorption of radiation normally occurs in the UV-Visible region of the spectrum. Optical absorption is a useful method for investigating optically induced transitions and for getting information about the band structure and energy gap of non-crystalline materials. The principle of this technique is that a photon with energy greater than the band gap energy will be absorbed. To study the optical properties like optical energy gap, oscillator strengths of different transitions possible in praseodymium doped glasses, we recorded absorption spectra of these glasses using an Ocean Optics CHEMUSB4-UV-VIS single beam spectrophotometer shown in Fig.3. The CHEMUSB4-UV-VIS consists of a USB4000 Spectrometer with a combination of deuterium tungsten halogen light source and 1 cm cuvette holder with high-speed electronics. The spectrophotometer covers 210 to 880 nm range, has optical resolution of 1.0 nm (FWHM) and captures 3648 wavelengths in less than 1 second. It sees changes as small as 0.01 Absorbance Units. The light source (far right) sends light via an input fiber into a cuvette in a cuvette holder (bottom center). The light interacts with the sample. The output fiber carries light from the sample to the spectrometer (top center) connected to the computer (far left).              European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  89   Fig.3: Ocean Optics CHEMUSB4-UV-VIS single beam spectrophotometer used for recording absorbance spectra of Pr6O11 doped zinc fluoroborate glasses.  The absorption spectrums of the glasses were recorded in a Ocean Optics USB4000-UV-VIS single beam spectrometer in both the UV and visible spectral region ranging from 200 nm to 700 nm. The spectra’s were obtained using software called Spectra Suite. Absorption spectra of zinc fluoroborate glasses recorded at temperature 300 K with 1.0 mol % Pr6O11 concentration are shown in Fig.4. The high phonon energy in borate glass is not detrimental to Sm3+ and Pr3+ normal 4f transition emissions, and sometimes it can accelerate the relaxation processes, which is necessary and beneficial for visible emissions. The absorption spectrum in visible region of 1.0 mol% of Pr6O11 doped borate glass demonstrates the suitability of borate glasses as a suitable host for Pr3+ .                                      Fig. 4 : Absorption spectrum of zinc fluoride glass doped with 1.0 mol % doped Pr3+.   The observed electric dipole transitions of Pr3+ involve primarily the excited states 3Pj (j=0, 1, 2) and 1D2 (Sharma, 2005).  Oscillator Strength  The assignment of the lines, their frequencies and the spectral oscillator strength (f x 10-6) are given in Table 3.The oscillator strength (f) corresponding to the different transitions was obtained by integrating the intensities of the absorption bands. It is given as 𝑓 =  𝑚𝑐2𝜋𝑁𝑒2�𝛼(𝛾|)𝑑𝛾|          𝑤ℎ𝑒𝑟𝑒  𝛼(𝛾)��� =ln �𝐼0(?̅?)𝐼(?̅?) �𝑡= 2.303 𝐸(𝛾)���/𝑡 where  m is the mass of electron, N is the number of rare earth ions, c is the speed of light, ?̅? is the wavenumber, 𝛼 (𝛾)���  is the absorbance, and t is the sample thickness. The oscillator strength is thus obtained (Hai Lin, 2005).    European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  90     Table 3: The assignment of the lines, their frequencies and the spectral oscillator strength (f X10-6) are given in table.  Wavelength (nm)  Energy  (cm-1)  Assignment  Oscillator Strength (*10-6) 438 22831.05 3P2 7.67 464 21551.72 3P1 3.99 476 21008.40 3P0 2.31 584 17123.28 1D2 9.13 The points shown in the Table 3 are specified in Fig.4 and we have found that the peak at wavelength 584 nm have maximum oscillator strength. This means that, the 1D2 transition has higher energy and this can be used to build lasers. Optical Band Energy Gap:  The experimental value of the absorption coefficient  () is calculated by using the equation, α (ω) = ( 2.303 * A ) / d  Theoretically, the optical band gap energy for indirect allowed optical transitions can be calculated. The quantity ( f)1/2 is plotted as a function of the photon energy (ђf) for glass sample doped with 1.0 mol % is as shown in the Fig.5. The straight portion of the graph is then extrapolated to intersect with x axis. The value of ђf at the point where ( f)1/2 becomes zero yields a direct measure of the optical band gap energy (Altaf,2005). The optical band gap energy was found to be 2.83eV.  Fig.5: A representative plot of the quantity (αђf) ½ as a function of the photon energy            (ђf). Glass Stability  The stability of the glass was measured by using Differential Scanning Calorimeter (DSC). Here glass stability was calculated by taking the difference of crystalline temperature (Tc) and glass transition temperature (Tg). Higher the value, higher is the glass stability. The stability of the glass doped with 1.0 mol % was found to be 120 and for undoped glass it is 50. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  91   Fig.6: DSC plots of 1.0 mol % Pr3+ doped zinc fluoride glass.  Conclusion  In the present study, the glass samples of composition [30 ZnF2 – 20 TeO2 – (50 – x ) B2O3 – x Pr6O11]  (where, x = 0.0, 0.1, 0.5, 1.0 and 1.5 mol %)  have been synthesized by normal melt-quench technique. The density and refractive index results show unusual behaviour with no particular trend in either increase or decrease of the outcomes. This might be because of the substitution of B2O3 oxides into Te2O3 where B2O3 plays a dual nature, it acts as network modifier and network former position for different concentrations of the dopant. The electronic polarizability for 1.0 mol% was found to be maximum compared to other glass samples [Table 1]. Stability of the 1.0 mol % doped glass was measured to be 120. The energy band gap of the doped glass mentioned above was found to be 2.83 eV. The absorption spectrum, gave the strength of 1D2  line to be maximum. In the present work, the glasses with more than 30% of zinc have been built which finds its applications in both photonics and optoelectronics fields.   References: Mahato, K. K.,  Rai,D.K.,1999, Optical Studies of  Pr3+ Doped Oxyfluoroborate  Glass, Phys. Stat. Sol.(a) 174, 277 – 289. Eraiah, B., 2006, Optical Properties of Samarium Doped Zinc – Tellurite Glasses, Bull. Mater. Sci., Vol 29, No. 4, 375-378.  Lin,H., Yang,D., Liu, G., Tiecheng, M., Bin, Z., Qingda, A., Jiayou,  Y., Xiaojun, W., Xingren, L., Edwin, Y., 2005, Optical Absorption and   Photoluminescence in Sm3+ and Eu3+ Doped Rare Earth Borate Glasses, Journal of  Luminescence,113,121–128. Weeranut, K., Jakrapong, K., Pichet, L., 2009, UV – VISIBLE – NIR Study Of Er3+ Doped Soda Lime Silicate Glass, International  Conference on the Role of Universities in Hands – On Education Rajamangala University of Technology Lanna, Chiang – Mai, Thailand.. European Scientific Journal    June  2013 edition vol.9, No.18    ISSN: 1857 – 7881 (Print)  e - ISSN 1857- 7431  92  Raghavendra, R., Rama, K., Udayachandran, T., Venkata, R., Reddy, Y.P., Sambasiva, R., Ravikumar, S.N., 2011, Effect of Li2O Content on Physical and Structural Properties of Vanadyl Doped Alkali Zinc Borate Glasses”, Physica B, 406, 2132 – 2137. Sharma, Y.K., Dubedi, R.P., Joshi, V., Karnataka K.B., Surana, S.S.L., 2005, Absorption Studies of Tripositive Praseodymium and Neodymium Doped Zinc Fluoride BoroPhosphate Glasses, Indian Journal of Engineering and Material Science,12, 65-74.  Altaf, M., Chaudhry, M.A., Siddiqi.S.A., 2005, Glass, Physics and Chemistry, Vol. 31, No. 5, 597-601.                                 

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CHARACTERIZATION OF Pr6O11 DOPED ZINC FLUOROBORATE GLASS

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