ОПТИКА И СПЕКТРОСКОПИЯ, 2014, том 117, № 1, с. 60-64
СПЕКТРОСКОПИЯ ^^^^^^^^^^
КОНДЕНСИРОВАННОГО СОСТОЯНИЯ
УДК 548.0:535.37
THE EFFECT OF EUROPIUM OXIDE IMPURITY ON THE OPTICAL AND PHYSICAL PROPERTIES OF LITHIUM POTASSIUM BORATE GLASS
© 2014 г. M. M. A. Maqableh*, S. Hashim*, Y. S. M. Alajerami*, **, M. H. A. Mhareb*,
R. S. Dawwud*, and A. Saidu*, ***
*Department of Physics, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia **Department of Medical Radiography, Al-Azhar University, Gaza Strip, Palestine ***Department of Physics, Usmanu Danfodiyo University, Sokoto, Nigeria E-mail: majdi.maq@gmail.com Received October 24, 2013
The most hosts that is utilized in scientific application is borate glass. By using melt-quenching technique, five samples of lithium potassium borate (LKB) doped with different concentration of europium oxide (Eu2O3) were prepared. To investigate the influence of dopant on the optical and physical characteristics of the proposed glass, two methods have been applied (XRD, PL). The amorphous nature was confirmed by X-ray diffraction (XRD). The physical parameters of the glass matrix doped by different oxidation state have been analyzed, these parameters are density, molar volume, ion concentration, inter-nuclear distance, and polaron radius. The exchange in the concentration of Eu+3 indicated the influence of Eu as a dopant on the photoluminescence (PL) emission of LKB glasses. The emission spectrum of LKB : Eu+3 show a chain of emission bands, which are attributed to the 5D0—7Fr (r = 1—4) transition of Eu+3. The luminescence studies showed four peaks 590 (yellow), 613 (orange), 650 (red), and 698 nm (red) for all samples except sample 0, the high luminescence efficiently is in emitting orange light at 613 nm.
DOI: 10.7868/S0030403414070149
INTRODUCTION
The formation of glass was determined first time by Zachariasen [1]. This theory describes a network structure for glass former, which is called continuous random network. There are many techniques which are used to prepare glass, but the most common one is melt-quenching technique which is based on melting the oxide then reducing the temperature sufficiently fast to brought the temperature lower than transition temperature (Tg). The most promising compounds in applied technology such as luminescence dosimeter is a borate glass, this significantly attributed to its attractive properties like phonon energy, low melting temperature, thermal stability and radiation, easy preparation and high transparency [2, 3].
The borate alone is found to be easy crystallized, fairly stable, and it has hygroscopic properties. In order to enhance its optical properties and diminish these drawbacks of borate glass, other reagents familiar as activator and modifiers must be append. These activators adding to glass structure in order to debilitate the bond strength, open up the structure, disrupt the glass lattice and reduce the viscosity of the glass [4, 5]. In order to enhance the optical and physical properties of glass, several alkaline oxides like BaO, ZnO, SrO, MgO, CaO, PbO, BiO2 and TeO2 were used in previous studies [6—11]. The most common modifier that is used in borate glass to improve its sta-
bility is lithium oxide, which make ionic links with oxygen atoms when added to glass mixture. To enhance the luminescence properties for lithium borate glass, several dopants were utilized as activators such as nickel, silver, magnesium, titanium, cerium, indium, europium, praseodymium, phosphorus, potassium, forum, manganese, copper, forum, dysprosium, cobalt, thulium, and lanthanum [12].
Thus, the main goal of the current study is to investigate the role of europium ions in the structure of different concentration of europium oxide doped in lithium potassium borate.
EXPERIMENTAL
Glass Preparation
Five samples of glass were prepared by melt-quenching technique by mixing powder form of host (B2O3) with the first modifier (Li2CO3), and second activator (K2CO3) for pure sample and adding europium with different concentration as dopant as listed in Table 1. The ratio of each component was clarified by the following compositions:
70B2O3 : 20Li2CO3 : (10 - x)K2CO3 : xEu+3, 0 < x < 1.
The preparation begins by weighting a powder form then mixed it together around 40 min. The mixture
THE EFFECT OF EUROPIUM OXIDE IMPURITY
61
was melted with an electric oven at 1100°C for duration of 50 min to ensure that all powder was molten [13]. The molten glass was transferred to another furnace quickly and poured on steel plate at 400°C for 4 h to avoid breaking and release thermal strain, this process called annealing. Finally, the samples were cooled to room temperature by average rate nearly 10°C min-1.
X-ray Diffraction
To obtain better results in XRD, the samples were milled and changed to powder form. This is very important to define the amorphous phase of the samples depending on X-ray diffraction to ensure the glasses were prepared and formed in amorphous state. This part was done by using Siemens diffractometer D5000 and the results were read and analyzed by using X'Pert High Score Plus soltware with copper target 40 kV and operated at 30 mA. The diffraction has been measured in the range of 20 from 10° to 80° with steps of 0.05° and 1 s counting time per step.
UV-vis-NIR Absorption Spectra
Glass samples in bulk forms were exposed to optical absorption spectrum to examine the light transition of the gap between two bands conduction and valance in the range between 200 and 1600 nm by using Shimadzu 3101 spectrophotometer. The photon energy gas an important impression on the optical absorption measurements [14]. By using the standard formula, the energy gap sharp edge can be more simply distinct for amorphous lattice compared to the crystalline lattice [15]:
Table 1. The raw material for all samples
E = hc/X,
(1)
where Eg is energy gap, h and c are constant (Plank's constant and speed of light respectively), and A is the wavelength, but for infinite absorption edge in non-crystalline material the process will be more complicated than defined state. In this case, we need to use other formula that was introduced by [16]. This formula is used to define the shape and absorption in region with high optical absorption features [16]:
a(®) = [h(®)u - E ]nA/h(®)u,
(2)
(n - 1 )/(n + 2) = 1 -JEg/20, where E is the direct optical band gap.
(3)
Glass
Batches composition, mol %
LÍ2CO3 B2O3 K2CO3 Eu+3
Sample 0 20 70 10 -
Sample 1 20 70 9.7 0.3
Sample 2 20 70 9.5 0.5
Sample 3 20 70 9.3 0.7
Sample 4 20 70 9.0 1.0
Photoluminescence Spectra
By using Perkin Elmer LS55 spectrophotometer, the PL spectrum was carried out with wavelength range 500—800 nm at room temperature in Department of physics, Universiti Teknologi Malaysia.
Physical Parameters
According to Archimedes principle, the density of glass samples (bulk form) was calculated, then molar volume was measured:
P
Wa
-x(Po - d)
+ d,
(4)
where p is the density of glass, p0 is the density of liquid (0.8669 g cm-3), wl is the weight of the samples in liquid, wa is the weight of the sample in air, and d is the density of air (0.001 g cm-3).
Vm = M/p, (5)
where Vm is the molar volume (cm3 mol-1), p is the density of glass, and M is the molecular weight.
According to following equation, the calculation of ions concentration is carried out inside the current samples [17]:
mole% of doped x glass density x NA
N =
average molecular weight of glass
(6)
In addition, more physical properties can be calculated by referring to Shelby and Ruller [17] as shown below.
Inter-nuclear distance:
where a(®) is absorption coefficient, ® is angular momentum, n is constant depending on state if direct or indirect (2 for direct and 1/2 for indirect), A is constant regarding to the scope of the band tailing. The refractive index is related through the equation
( Â ) = ( 1 /N)1/3,
polaron radius:
rp ( Â ) = ( 1/2 )(n /6 N)1/3.
(7)
(8)
The oscillator strength may be calculated by two formulas depending on the absorption peaks [18]. For absorption peaks with Gaussian shape, we can use following equations for other shapes:
fexp = 4.32 X 10-9 Je(v)dv,
(9)
62
Intensity, arb. un. 800
400 I-
MAQABLEH et al.
40
80
29, deg
Fig. 1. XRD spectrum for LKB : Eu 1 (2), 2 (3), 3 (4), 4 (5).
+3
samples 0 (1),
Absorption, arb. un.
\ 5 7f0^5L
2000
1200
400 350
450
550
Wavelength, nm
Fig. 2. UV-vis spectra in the range of 350—600 nm for
LKB : Eu+3 - samples 0 (1), 1 (2), 2 (3), 3 (4), 4 (5).
where s(v) is the molar absorption coefficient at given energy v (cm-1),
fexp = 4.32 X 10-9 JAv,
(10)
where Av is the width of the band at half the peak intensity.
RESULTS AND DISCUSSION
For purpose of confirming the current results, all analysis were run and repeated about three times. It appears there is no any distinct variation in the general peak position and shape of the spectra. This mean all our results are within the error bars which prove the samples of the synthesis.
The crystalline nature is truant in the current glass and completely amorphous phase appeared from the XRD as shown in Fig. 1. The diffraction shapes show a huge peak. It verifies that the prepared samples are fully amorphous and they do not show any crystalline phase.
The absorption spectra of Eu3+ doped (10-z)K2CO3 : 20Li2CO3 : 70B2O3 : zEu2O3 (z = 0, 0.3, 0.5, 0.7, 1.0) glasses is shown in Fig. 2. Five bands were observed in LKB doped with Eu+3 corresponding to the excited levels of Eu3+ ions. The bands at 388, 463, 530, 582 and 1416 nm were assigned to absorption peak of 5L7,5D2, 5D1, 5D0, and 7F2 respectively.
According to the curve obtained from UV-absorption, the energy band gaps were able to be measured experimentally. These curves explain the connection between the determined energy Eg from Eq. (1) and the square root of absorption (aE)1/2. Table 2 summarize the influence of different concentration of eur
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