Effect of Dy2O3 impurities on the physical, optical and thermoluminescence properties of lithium borate glass

Author’s Accepted Manuscript Effect of Dy2O3 impurities on the physical, optical and thermoluminescence properties of lithium borate glass M.H.A. Mhareb, S. Hashim, S.K. Ghoshal, Y.S.M. Alajerami, M.J. Bqoor, A.I. Hamdan, M.A. Saleh, M.K.B. Abdul Karim www.elsevier.com/locate/jlumin

PII: DOI: Reference:

S0022-2313(16)30180-6 http://dx.doi.org/10.1016/j.jlumin.2016.05.002 LUMIN13973

To appear in: Journal of Luminescence Received date: 8 February 2016 Accepted date: 2 May 2016 Cite this article as: M.H.A. Mhareb, S. Hashim, S.K. Ghoshal, Y.S.M. Alajerami, M.J. Bqoor, A.I. Hamdan, M.A. Saleh and M.K.B. Abdul Karim, Effect of Dy2O3 impurities on the physical, optical and thermoluminescence properties of lithium borate glass, Journal of Luminescence, http://dx.doi.org/10.1016/j.jlumin.2016.05.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of Dy2O3 impurities on the physical, optical and thermoluminescence properties of lithium borate glass M.H.A. Mhareb1*, S. Hashim2, S.K. Ghoshal2, Y.S.M. Alajerami3, M.J. Bqoor1, A.I. Hamdan1, M.A.Saleh4, M.K.B. Abdul Karim2 1

Radiation Protection Directorate, Energy and Minerals Regulatory Commission, Amman 11810, Jordan

2

Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia 3

Department of Medical Radiography, Al-Azhar University, Gaza Strip, Palestine

4

Nuclear Engineering Programme, Faculty of Petroleum and Renewable Energy Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia *Author for correspondence: [email protected] (Mohammad Abu Mhareb) [email protected] (Sib Krishna Ghoshal)

Abstract Dysprosium (Dy) doped lithium borate glass (LBG) is prepared using conventional meltingquenching technique with varying Dy concentration in the range of 0 to 1.0 mol%. Prepared glass samples are characterized via X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR), UV–Vis–IR, Photoluminescence (PL), Thermoluminescence (TL) spectroscopy and Differential Thermal Analysis (DTA). The physical parameters such as the density, optical energy band gap, oscillator strength, refractive index, ion concentration, Polaron radius, molar volume and inter-nuclear distance are determined. UV–Vis–IR spectra revealed seven prominent bands centered at 448, 749, 796, 899, 1085, 1265 and 1679 nm corresponding to the transition from the Dy3+ ion’s ground state (6H15/2 ) to the excited states (4I15/2,6F3/2, 6F5/2, 6H5/2, 6F9/2, 6H9/2 and 6H11/2). The room temperature photoluminescence (PL) spectra of the glass series at 350 nm excitation displayed two peaks centered at 481 nm and 573 nm, which are assigned to the transitions of (4F9/2 → 6H15/2) and (4F9/2 → 6H13/2), respectively. The TL spectra of gammairradiated samples are measured, which showed Dy3+ content dependent simple glow peak at 190 ºC. Dysprosium ion is found to play an important role in the TL and PL intensity enhancement of LB phosphor.

Keyword: Lithium borate, Optical properties, Photoluminescence, Thermoluminescence.

Introduction Certainly, optical properties evaluation provide very useful information on optically induced transitions and an insight into the energy gap and band structures of crystalline and noncrystalline phosphor materials. Borate is one of the best and most well-known glass formers. It possesses several attractive features such as ease of preparation, good host for alkali, alkaline earth and rare earth ions, higher relative stability and most importantly it is inexpensive [1-3]. Thus, borate glass (BG) has attracted great interest among researchers especially as TL material because of its possible applications as laser host, lamp phosphor, in photonic devices and in dosimetry for various applications including radiotherapy. Depending on the composition BG network is composed of BO3 triangular units and BO4 tetrahedral units. The addition of other cations (alkali, alkaline earth and transition metals) as network modifiers to BG can affect the functional group and consequently converts the BO3 triangular units to BO4 tetrahedral units. The initial addition of modifier to boron oxide (B2O3) results in the conversion of BO3 to BO4 without the formation of non-bridging oxygen (NBO). However, the number of BO4 units increases remarkably with the increase of modifier concentration reaching a maximum. Afterwards, BO4 units start to decline due to the formation of BO3 combined with NBO. [4]. BO4 units are greatly responsible for enhancing the luminescence and to creating the color centers [5]. However, the hygroscopic nature of borate particles must be reduced with the destruction of the closed network and the creation of new linkages. Many efforts have been dedicated to reduce and control the hygroscopic characteristics of boron compositions [6-10]. Lithium is widely used in many glass formers like borate to reduce the melting point and viscosity as well as to improve the physical properties. Lithium is known to increase the stability of the borate glass by converting BO3 to BO4, which acts as a vacancy creator to increase the dislocation. Besides, lithium as a modifier can reduce the hygroscopic nature of borate and improves the stability by forming ionic bonds with oxygen (NBO). Actually, these bonds are responsible for the formation of color centers [10,11]. In addition, there are no energy levels within 10 eV that give the impression of providing luminescence activation especially at high doses [12]. Zachariasen (1932) reported the role of alkali ions as a modifier, where they are found to break up the continuous glass forming network to create NBO. Several studies revealed

the effectiveness of lithium as a modifier [6,13]. LB glasses exhibit good solubility of rare-earth ions suitable for laser hosts and optical fiber applications, high thermal stability, high transparency, and low melting point. Lately, several studies have been carried out to investigate the performance of lithium borate doped with transition metals or rare earth elements [9,10,14,15]. The TL and optical properties of rare-earth (RE) Dy3+ ions doped LB glasses are not much explored despite their similarities with other luminescent glasses. Earlier, various RE ions are extensively used as dopants to achieve highly efficient lasing action. The RE elements are advantageous because of enhanced light emission and capacity to create a broad spectral range. Among various RE, Dy3+ ions are recognized to be the best one for developing solid state lasers in amorphous and crystalline state. The two PL bands of Dy3+ ion that are most intense in the visible spectral region corresponds to 4F9/26H15/2 (blue) and 4F9/26H13/2 (yellow) transitions [3, 16-19]. In this view, this paper takes an attempt to inspect the influence of varying Dy2O3 impurity concentrations on the structural, physical, optical and TL properties of melt-quench synthesized LB glasses. Various characterizations and performed, results are systematically anlyzed and compared.

Materials and methods The conventional melt-quenching method is utilized to prepare a series of LB glass samples at different concentrations of Dy2O3 impurities. Dy3+ ions doped LB glasses of nominal compositions 30Li2O-(70-x)B2O3-xDy2O3, with x = 0, 0.3, 0.5, 0.7 and 1.0 mol% are synthesized. Analytical grade high purity glass constituents (Sigma Aldrich, 99.99%) such as Li2O, B2O3 and Dy2O3 in the powder form are well mixed in an alumina crucible before being melted in a electrical furnace (1200 °C) for one hour. Molten mixture is frequently stirred until a bubble-free fluid is achieved with desired viscosity, which is then poured into a pre-heated steel mould and annealed at 350 °C (below the glass transition temperature) for 3 hours to remove residual internal strains that cause embrittlement. Finally, the temperature is gradually reduced to room temperature following a cooling rate of 10 ºC min1. Solid samples are cut and polished to get the transparent appearance for further characterizations. Table 1 enlists the chemical composition of the prepared glasses with sample codes.

The amorphous nature of the prepared samples is analyzed using XRD measurement (PANalytical XRD diffractometer model PW 3040 MPD attached to an Xpert Data Viewer). Samples are crushed in to powder form and exposed to X-rays (λ=1.54 Å) at 40 kV and 30 mA and with 2θ varying from 10° to 90°. The functional groups (bonding vibrations) of the glass network are analyzed using FTIR spectroscopy (Perkin Elmer). FTIR attenuated total reflectance (ATR) is used to optimize the present analysis, where the solid glass samples are first ground before being made in to direct contact with the ATR crystal. Thin pellet samples are then attached to the sample holder. The IR scans in the wave number range of 4400–500 cm1 with a resolution of 0.8 cm1 are used (three repetitions for each scan). DTA measurement is performed on a PerkinElmer analyzer to determine the thermal stability of prepared samples, which is equipped with a Cu target and nickel filter. A heating rate of 10 °C min1 in the temperature range of 50–1000 °C is used. A Shimadzu 3101 UV–Vis–NIR spectrophotometer is used to record the absorption spectra in the wavelength range of 200–2000 nm. The room temperature emission spectra are obtained using a Perkin Elmer LS55 spectrofluorometer comprised of a 150 W Xenon lamp, monochromator and detector. The TL measurement is carried out at the Secondary Standard Dosimetry Laboratory (SSDL) at the Malaysian Nuclear Agency. Samples are irradiated using 60Co gamma source. Read-out of all samples is performed with a TLD reader (Model 4500 Harshaw, USA) at a linear heating rate of 5 ºC s1. Following Davis and Mott relation, the optical band gap (Eg) is calculated from the absorption edge via [20]:

(1)

where α denotes the absorption coefficient and A is a constant. The refractive index (n) is obtained using the expression [21]:

2)

Using the absorption spectrum, the oscillator strength that characterizes the intensity of spectral lines absorbed by the glass sample is estimated [22]:

(3)

where ε(υ) is the molar absorption coefficient at a given energy υ (cm1). The room temperature glass density (ρ) is determined using Archimedes method with toluene (99.99% purity) as immersion liquid, which is chosen because its non-absorbing nature. The density yield:

(4)

where a is the weight of glass in air, b is the weight in toluene, and 0.865 g.cm3 is the room temperature density of toluene. The molar volume (Vm) yields:

(5)

where M is the molecular weight of the glass sample. The average boron-boron separation ˂dB-B> that identifies the effect of dopant concentration in the glass matrix is given by [23]:

(6) with volume of boron atoms per mole (

): (7)

where NA represents Avogadro’s number and XB is the mole fraction. Ion concentration (N) is calculated via:

(8)

where mole% refers to the dopant, and Mi is the average molecular weight of the prepared glass. The Polaron radius yields: (9)

The inter-nuclear distance is given by:

(10) The field strength (F) of dopant in the glass matrix is expressed in terms of the atomic number (z) and the Polaron radius (rp) of the dopant as:

(11)

Results and discussion Figure 1 shows the typical XRD pattern of all prepared LB glass samples. The presence of broad hump in the absence of any sharp crystalline peaks verifies the true amorphous nature of prepared glass with varying Dy2O3 contents. Table 2 summarizes the calculated physical parameters of the synthesized Dy3+ ions doped LB glasses. Figure 2 displays the Dy2O3 contents dependent variation in the density and molar volume. The glass density is found to gradually increase and the molar volume is reduced with the increase of Dy3+ ions concentration. This increase in the glass density is attributed to the replacement of lighter (in terms of atomic mass) boron atoms by heavier Dy2O3 compound. Besides, the reduction in the molar volume indicates the compactness of the glass structure [11]. Generally, the main factors that affect the density of the glass are the atomic size and atomic mass of the dopant Dy3+ ions. The increase of Dy2O3 concentration caused an increase of oxygen–boron ratio in the glass network, and led to compact the structural network.

The observed considerable decrease in the inter-nuclear distance (ri) and Polaron radius (rp) with the increase of dopant concentration (Table 2) is ascribed to the congestion of dopant in the glass host [11]. This decrease in the rp values with increasing Dy2O3 is most likely related to the increased value (N) of Dy ions. Furthermore, the overcrowding of the glass network by dysprosium interstices reduced the average RE–oxygen distance. Consequently, the significant enhancement in the field strength is due to the appearance of strong links between the Dy3+ and B ions in the glass matrix. This link is formed through the possible displacement of the Dy3+ ions with newly generated oxygen atoms from the conversion of BO3 to BO4 units. Besides, the decrease in the bond lengths or boron-boron distance is ascribed to the emergence of stretching force of the bonds in the glass network [11, 24]. In the average boron–boron separation, the value of

depends on the cations concentration in the glass host, which is strongly related to

the ionic radius. With the introduction of Dy2O3 in to the amorphous matrix, a reduction in the boron–boron separation is observed. Figure 3 depicts the IR spectra of all glasses at different concentrations of Dy3+ ions. Three vibrational bands are allocated to the B-O stretching modes of trigonal BO3 units (1348–1370 cm1), B-O stretching of tetrahedral BO4 units (1048–1051 cm1) and the bending of B-O-B linkages in the borate network (700–704 cm1). The peak positions with their band assignments are outlined in Table 3. The intensity of the BO4 band is enhanced with increasing Dy2O3 content up to 0.7 mol%, indicating an increase of the vibration and the bond length of B– O groups as well as the formation of BO4 units [10,25]. However, the influence of Dy2O3 variation on the general structure of LB glass remains insignificant. The appearance of BO4 units in the prepared glasses is due to the introduction of modifiers inside the glass network. The inclusion of alkaline or alkali earth oxides to the glass host led to an alteration of BO3 units into BO4 by generating NBO bonds. Figure 4 illustrates the DTA curve for sample S6. The values of transition temperature for glass (Tg), crystal (Tc) and melting (Tm) are listed in Table 4. The parameter S = Tc-Tg is used to characterize the glass stability. Glass is said to be thermally stable if S > 100 °C. Hruby parameter [26] that measures the tendency of a system to become a glass rather than a crystal is given by:

(12)

Generally, it is difficult to prepare glasses with HR ≤ 0.1. Otherwise, higher stability is achieved with large HR value [27]. The obtained value of HR for S2 sample is 1.19, indicating excellent glass forming ability and high thermal stability. This result provides clear indication that the prepared glass is useful for different applications Figure 5 demonstrates the Dy2O3 concentration dependent absorption spectra of synthesized samples. An optical absorption spectrum of the prepared glass represents the wavelength of light responsible for the electronic transitions within the material. Glass without Dy2O3 does not exhibit any absorption peak while glasses containing Dy2O3 display numerous absorption peak of Dy3+ ion corresponding to different transitions between the ground state and excited energy states inside the electronic configuration of Dy3+ ions. The absorption spectra reveal seven prominent bands in the range of 350–1900 nm, which are centered at 448, 749, 796, 899, 1085, 1265 and 1679 nm. They are assigned to the transition from the Dy3+ ion’s ground state (6H15/2 ) to the excited states (4I15/2,6F3/2, 6F5/2, 6H5/2, 6F9/2, 6H9/2 and 6H11/2), respectively. Furthermore, the RE ions display some highly sensitive and intense absorption peaks called hypersensitive transition conforming the selection rule │∆S│= 0, │∆L│≤ 2 and │∆J│≤ 2 [28]. A hypersensitive peak centered at 1265 nm corresponding to the 6H15/2→ 6H9/2 transition is manifested. The intensity of this hypersensitive transition is determined by the ion-ligand bonding environment [29]. Table 5 summarizes the oscillator strength for each peak. Figure 6 shows the Dy2O3 concentration dependent variation in the optical band gap energy for prepared glass system. Table 6 enlists the calculated values of optical band gap energies for different samples. The value of energy band gap is found to decrease with the increase of Dy3+ ions contents, which is attributed to the structural modifications in the glass network. It is perceived that the addition of Dy3+ ions in the amorphous matrix may enhance the degree of localization by creating defects in the charge distribution. Consequently, the energy levels of the closest oxygen ions are driven nearer to the top of the valence band and thereby raising the number of donor centers in the glass matrix. This increase in donor centers leads to a decrease in the energy band gap values [3,24]. Urbach energy is a measure of disorder in amorphous solids, where higher Urbach energy values signify more glassy nature. A plot of ln(α) versus hυ as shown in Figure 7 is generated to

calculate the Urbach’s energy (from inverse slope). The observed increase in the Urbach energy (Table 6) is attributed to the formation of bonding defects and generation of more NBO. For amorphous semiconductors these values lie within the range of 0.046–0.66 eV, which is also obtained for the present glass system. The room temperature luminescence spectra with 350 nm excitation are illustrated in Figure 8. Two emission bands centered at 481 and 573 nm are allocated to the transitions of (4F9/2 → 6H15/2) and (4F9/2 → 6H13/2), respectively [3]. The intensity of PL emission is found to enhance at 0.5 mole% of Dy2O3 and then gradually reduced at higher concentration. This reduction in the PL intensity is ascribed to the RE’s concentration quenching phenomenon. The substitution of dysprosium and oxygen inside the glass creates large number defects and alters the glass network structures. These defects enhance the rate of multiphonon processes and lead to nonradiative transitions. Figure 9 represents the partial energy level diagram of Dy3+ ions, which is used to describe absorption, emission transitions and other processes such as cross relaxation, nonradiative and radiative energy transfer, and ground state absorption upon excitation. First, the Dy3+ ions are excited by 350 nm radiation from the ground state (6H15/2) to the most excited level (4M15/2, 6P7/2), which is then decayed non-radiatively to 6F9/2 states before making downward transition radiatively to 6H15/2 and 6H13/2, giving blue and yellow emissions, respectively. Figure 10 displays the Dy2O3concentration dependent glow curve of LB glass system irradiated with 3 Gy

60

Co gamma dose. A simple glow curve with a single peak at 190 °C is

evidenced. The TL intensity exhibits a maximum at 0.5 mol% of Dy3+ (S2 sample) and gradually quenches beyond this concentration [30], which is attributed to the saturation of created electron traps [19,31]. Following the mechanisms of Porwal [32] and Annalakshmi [33], the TL properties of the proposed dosimeter are explained. The identified defect centers such as borate radicals (BO3)2 and oxygen vacancies (

) are found to form during gamma irradiation and are

responsible for the TL process. The observed TL glow curves can be interpreted via the following processes:

(i) Irradiation yields LB: Dy3+ → (BO3)2, (

)

and (ii) Heating causes (BO3)2→ (BO3)3 + h, [Ov] + h → [Ov]* → Dy3+* → Dy3+ + h. As aforementioned, in Dy3+ doped LB phosphors the TL response are majorly due to the gamma irradiation assisted formation of borate radicals and oxygen vacancies. Upon heating, the borate radical releases the hole which in turn recombines with the electron trapped at the oxygen vacancy, resulting in the release of recombination energy. Then the energy released from the Dy3+ recombination essentially excites the Dy ions and originates the characteristic light emission. The TL features of the Dy3+ dopant in LB phosphors can be understood in terms of the non-radiative energy transfer from the excited oxygen vacancy-related defects to the nearby Dy3+ ions. Figure 11 reveals the dose response of S2 sample subjected to

60

Co gamma irradiation

within the dose range of 0.01 to 4 Gy. Excellent dose linearity is achieved with a good linear correlation coefficient of 0.997. This result offers the preference of using this dosimeter in medical purposes.

Conclusion The Dy3+ doped LB glasses are prepared using conventional melt-quenching technique to inspect the influence of Dy3+ ions concentration on physical, structural, optical and TL properties. Thermally stable and transparent glass samples are achieved. Glass samples are characterized via XRD, FTIR, DTA, UV-Vis, PL, and TL measurements. The substitution of Dy2O3 considerably affected the physical, structural optical properties and TL properties of the prepared phosphor. The density is increased and molar volume decreased with increasing Dy2O3 contents into the glass network. XRD patterns confirmed their amorphous nature. FTIR spectra revealed the existence of three vibrational bands (BO3, BO4 and bending of B-O-B linkages) in the borate network. Thermal stability of S2 sample is found to be greater than 100 ºC, which is useful for different applications. The observed values of Urbach energy are in the range of 0.328 and 0.335 eV, which indicated more disordered (amorphous) state of obtained glasses. Seven absorption bands are observed around 448, 749, 796, 899, 1085, 1265 and 1679 nm with different relative

intensities, which are assigned to the transition from the ground state 6H15/2 → 4I15/2, 6H15/2 → 6

F3/2, 6H15/2 → 6F5/2, 6H15/2 → 6H5/2, 6H15/2 → 6F9/2, 6H15/2 → 6H9/2 and 6H15/2 → 6H11/2 to the

excited state of Dy3+ ion, respectively. The PL intensity for both blue and yellow peaks of these glasses at 350 nm laser excitations is enhanced. These glasses displayed a simple glow curve with a single prominent peak at 190 ºC and linear dose response up to 4 Gy. These admirable properties of the proposed glass compositions make them highly potential for different photonic application, laser, and radiation dose monitoring.

Acknowledgments The authors are grateful to the Ministry of Education-Malaysia and UTM for providing financial assistance through the Fundamental Research Grant Scheme (FRGS), Vote number (R.J130000.7826.4F168, 4F424) and GUP/RU (10H60, 12H42).

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[29] P. Pascuta, L. Pop, S. Rada, M. Bosca, E. Culea, J. Mater Sci- Mater El. 19(5) (2008) 424428. [30] S.P. Puppalwar, S.J. Dhoble, N.S. Dhoble, Animesh Kumar. Nucl. Instrum. Meth. 274 (2012) 167-171. [31] M.H.A. Mhareb, S. Hashim, S.K. Ghoshal, Y.S.M. Alajerami, M.A. Saleh, N.A.B. Razak, S.A.B. Azizan. Luminescence 30 (8) (2015) 1330-1335. [32] N.K. Porwal, R.M. Kadam, T.K. Seshagiri, V. Natarajan, A.R. Dhobale, A.G. Page. Radiat. Meas. 40(1) (2005) 69-75. [33] O. Annalakshmi, M.T. Jose, U. Madhusoodanan, J. Sridevi, B. Venkatraman, G. Amarendra, A.B. Mandal. Radiat. Effects and Defects in Solids 169(7) (2014) 636-645. Figure caption Figure 1 XRD spectra obtained for LMB doped with different concentration of Dy2O3. Figure 2 Density and molar volume relation of LB glasses doped with different concentrations of Dy2O3. Figure ‎3 IR spectra of LB glasses doped with different concentrations of Dy2O3. Figure 4 DTA curve for S2. Figure 5 Optical absorption spectra of LB doped with different concentrations of Dy2O3. Figure 6 Optical energy band gap of LB doped with different concentration of Dy2O3. Figure 7 Urbach energy of LB doped with different concentration of Dy2O3. Figure 8 PL emission spectra for LB doped with different concentration of Dy2O3. Figure 9 Partial energy levels of Dy3+ ions showing different processes and transitions. Figure 10 TL glow curves of LB doped with different concentrations of Dy2O3. Figure 11 Dose response of LB:Dy (S2) subjected to gamma of Gy.

60

Co irradiation at 0.01 up to 4

Table 1: Nominal chemical composition of prepared glasses samples (mole%).

Glass Code

Composition (mol%) Li2O

B2O3

Dy2O3

S0

30

70.0

0.0

S1

30

69.7

0.3

S2

30

69.5

0.5

S3

30

69.3

0.7

S4

30

69.0

1.0

Table 2: Physical parameters calculated for LB doped with different concentration of Dy2O3.

Measurements 3

ρ (g cm ) Vm (cm3 mol1) N x 1022 (ion cm3) rp(Å)  108 ri(Å)  108 F x 017 (cm2)  108 nm

S0 2.254 25.591     4.137

S1 2.291 25.576 0.706 2.100 5.211 3.684 4.122

Glass code S2 2.318 25.543 1.178 1.770 4.393 5.184 4.112

S3 2.348 25.476 1.654 1.581 3.924 6.499 4.099

S4 2.386 25.444 2.366 1.403 3.482 8.250 4.084

Table 3: IR peak positions and band assignments for glass series.

Glass code

B-O stretching of trigonal BO3 (cm1)

B-O stretching of tetrahedral BO4 unit (cm1)

Bending vibration B-O-B (cm1)

S1

1348

1051

700

S2

1348

1048

704

S3

1370

1051

704

S4

1348

1051

704

Table ‎4: Thermal parameters obtained from DTA traces of S2. Sample

Tg (°C)

Tc (°C)

Tm (°C)

Tc-Tg (°C)

HR

S2

475

640

778

165

1.19

Table 5: Variation of transition levels and oscillator strengths of prepared glass.

Absorption Transition

Wavelength (nm)

Energy (cm1)

6

H15/2→ 4I15/2

448

6

H15/2→ 6F3/2

6

Oscillator Strength f ( 104) S1

S2

S3

S4

22321

2.45

3.17

3.99

5.13

749

13351

6.39

8.22

8.92

10.11

H15/2→ 6F5/2

796

12562

1.84

2.29

3.23

4.43

6

H15/2→ 6H5/2

899

11123

0.89

1.56

2.43

3.23

6

H15/2→ 6F9/2

1085

9216

0.22

0.46

0.87

1.05

6

H15/2→ 6H9/2

1265

7905

0.01

0.02

0.03

0.05

6

H15/2→ 6H11/2

1679

5955

0.02

0.04

0.06

0.08

Table 6: Energy band gap, Urbach energy, refractive index and cutoff wavelength of prepared glass.

S0

Energy Band Gap 3.474

Urbach Energy 0.328

Refractive Index 2.279

Cutoff Wavelength (nm) 383

S1

3.442

0.334

2.287

387

S2

3.493

0.335

2.275

387

S3

3.388

0.343

2.299

404

S4

2.372

0.340

2.590

395

Glass Code

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11