ОПТИКА И СПЕКТРОСКОПИЯ, 2013, том 114, № 4, с. 585-591
СПЕКТРОСКОПИЯ КОНДЕНСИРОВАННОГО СОСТОЯНИЯ
УДК 535.37
THE EFFECT OF MgO ON THE OPTICAL PROPERTIES OF LITHIUM SODIUM BORATE DOPED WITH Cu+ IONS
© 2013 г. Yasser Saleh Mustafa Alajerami*, **, Suhairul Hashim*, Wan Muhamad Saridan W&n Hassan*, Ahmad Termizi Ramli*, Muneer Aziz Saleh*, **
* Department of Physics, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia ** Department of Medical Radiography, Al-Azhar University, Gaza Strip, Palestine E-mail: Yasser_ajr@hotmail.com Received April 19, 2012
The current work presented the photoluminescence (PL) properties of a new glass system, which are reported for the first time. Based on the attractive properties of borate glass, a mixture of boric acid (70-x mol. %) modified with lithium (20 mol. %) and sodium carbonate (10 mol. %) was prepared. The current study illustrated the effect of dopant and co-dopant techniques on the lithium sodium borate (LNB). Firstly, 0.1 mol. % of copper ions doped with LNB was excited at 610 nm. The emission spectrum showed two prominent peaks in the violet region (403 and 440 nm). Then, we remarked the effect of adding different concentration of MgO on the optical properties of LNB. The results showed the great effect of magnesium oxide on the PL intensities (enhanced more than two times). Moreover, an obvious shifting has been defined toward the blue region (440—«-475 nm). The up conversion optical properties were observed in all emission spectra. This enhancement is contributed to the energy transfer from Mg2+ ions to monovalent Cu+ ion. It is well known that magnesium oxide alone generates weak emission intensity, but during this increment the MgO act as an activator (co-doped) for Cu ions. Finally, energy band gap, density, ion concentration, molar volume, polaron radius and inter-nuclear distance all were measured for the current samples. The current samples were subjected to XRD for amorphous confirmation and IR for glass characterization before and after dopants addition. Finally, some of significant physical and optical parameters were also calculated.
DOI: 10.7868/S0030403413040223
INTRODUCTION
The glassy materials play a significant role on the progress of humanitarian issues. Their multidisci-plinary using attributes to the unique properties that owned this system. The borate glass, one of the most promising glasses, is widely exploited in the last four decades in various medical and industrial fields [1, 2]. This system proved its efficiency in term of its easy preparation and shaped, highly transparence, ionic conduction, inexpensive and relative stable [3, 4]. Moreover, the borate glass considers as a good host for different metals (transitions and rare earths). Numerous researches have been done to enhance the efficiency of the borate glass. These efforts were focused on adding modifiers (alkali/alkaline) and/or activators. The lithium is one of the earlier modifiers that it is used as vacancies' creator to increase the host strengthens (mechanical stability) of borate glass. Regarding to the energy levels of lithium ion, the minimum energy level of lithium is around 10 eV, so we can assume that it does not affect directly in the luminescence, but it acts as an activator during the exposing process [5]. Sodium is another alkali metal that showed attractive results as a modifier in borate network [6—9]. The sodium follows the [Ne] 3^1 electronic configuration that a free electron is found in the
outer L-shell. This isoelectric sequence distribution describes the extreme stability of sodium, particularly after the loss of the extra electron on the 3s level [10]. The adding of sodium to the borate system tends to strengthen its network; beside this we expect the enhancement of luminescence intensity after the excitation process of photoluminescence spectrum.
Several metals were used as dopants to improve the luminescence property of borate glass, indium, nickel, cerium, silver, europium, titanium, praseodymium, potassium, chromium, cobalt, dysprosium, iron, lanthanum, thulium, phosphorus, copper and manganese. Many studies remarked the efficiency of copper ions on the luminescence spectrum. According to Puppalwar and co-workers [11], the monovalent Cu+ show well-defined luminescence properties corresponding to the cross-relaxation of Cu+ ions.
3d104s1 3dV — 3d10, Cu° —»- (Cu+)* —— Cu+ cross-relaxation transition.
On the other hand, it was explored that the samples that showed low luminescence intensity involved a significant amount of copper as Cu++ [12]. As well as, the increment of copper ions with specific concentration enhances the luminescence properties; as well as above this specific concentration an adverse behaviour was
obtained attributed to the quenching saturation [11, 13]. In the present work, we intend to explore the efficiency of MgO as co-activator with 0.1 mol. % of Cu ions on the lithium sodium borate glass.
EXPERIMENTAL
Glass Preparation
The current samples were prepared by the melt quenching technique. A high purity chemicals (99.999%) on the powder form were obtained from Sigma-Aldrich Company, and mixed mechanically for 40 minutes. The selected glass host was the boric acid (H3BO3), and each of lithium (LiCO3) and sodium (Na2CO3) carbonate was added as modifier. Based on the literature, a fixed concentration of copper was used as first dopant. Different concentration of MgO was added to explore its effect on the luminescence spectrum. The milled mixture was poured on alumina crucible and inserted on electrical furnace at 1200°C for 50 minutes. After recurrent shake, a clear, homogenous and bubble free melts was obtained. The molten glass was casted on a steel plate, pressed and shifted to another furnace at 400°C for three hours annealing. Finally, the temperature was reduced to the room temperature with a reduction rate 10°C/min. To check the reproducibility of the current samples, the fifth samples were prepared through three batches, and three readings were carried out for each sample under the same temperature and humidity conditions as shown in Table 1.
Photoluminescence Spectra and Physical Measurements
X-ray diffraction. The vitreous phase of the current samples was checked by X-ray Diffractometer (Siemens D5000). At the ambient temperature, the software provided an incident photon with 1.54 A and started at 40 kV and 30 mA. The threshold range for 20 angle was 10° to 90°. The detection was carried in steps of 0.05° and 1 counting per second. For more
precise results the samples were placed on the powder form.
FTIR spectroscopy. For IR analyzing, the samples were crushed and prepared as thin pellets with potassium bromide (KBr). The mixture was prepared by milling the KBr with the proposed samples and pressed with five tones pressure. Transparent pellets were obtained with 5 mm diameter and 1mm thickness. To avoid any systematic error, three samples for each dopant were prepared and analyzed with using wave number range 4400—400 cm-1 and instrument resolution of 0.8 cm-1.
Density and molar volume. Based on Archimedes method, we determined the density of our samples. For more accuracy, we used the toluene (99.99% pure) as immersion fluid and the measurements were repeated three times.
P = HS-x 0-865 g/cm3, (1)
(a - b)
where, P is the density, a is the weight of the sample in air, b is the weight of the glass sample in toluene and 0.865 is the density of toluene. All measurements were done at room temperature (27°C).
Consequently, the molar and the specific volume were also calculated.
Vm = M (cm3/mole), (2)
P
where, Vm is the molar volume, M is the molecular weight.
Vs = 1. (3)
P
Ion concentration. The ions' concentration inside the current samples can be calculated by using the following formula [14]:
N _ mole % of doped x glass denisity x N A (ion/cm 3) Average molecular weight of glass
(4)
(Ä) _ 1 ( V 7 2(6N
1/3
Inter-nuclear distance
" (Ä) _ (N
1/3
According to Shelby and Ruller [15], two other related physical properties can calculate after the determination of ion concentration as shown below: polaron radius
(5)
(6)
UV-Vis-NIR absorption spectra. Both of energy band gap and refractive index were defined by using the visible and near region spectrometer. Initial parameters for parameters calculation were revealed from Shimadzu 3101 UV-Vis-NIR spectrophotome-ter. For band gap and reflection parameters, a photo-multiplier detector with R = 928, slit 20 degree and wave length range 200-900 nm were employed to interpret the retrieved signals. The value of optical absorption's edge for each doped were identified; then
r
Intensity, a.u. 200 r
150
100
50
20
40
60
80
29, deg
Fig. 1. XRD pattern obtained for Li2CO3-Na2CO3-H3BO3: 0.1 mol. % CuO and MgO.
the absorption coefficient for both direct and indirect transitions were calculated by using Tauc formula [16],
monochromator equipped with a photodiode detector at particular excitation wavelength.
a(to) = ( h (to) v - E) nA/h (to) v,
(7)
where a(to) is the absorption coefficient for direct and indirect transitions based on the value of n (1/2 for direct transition and 2 for indirect transition), to is the angular frequency, A is a constant related to the extent of the band tailing and Eg is the optical energy gap.
The second parameter obtained from the UV-Vis-NIR spectrophotometer was the reflection value for each doped. The reflection spectrum was determined with the same mentioned parameters. The obtained reflection value (R') was normalized (R) then inserted in the Fresnell's Equation:
2 ( 1 + R1/2 ) n = ----.
(1 - R 1 /2 )
(8)
Finally, data fit software version 9.059 was used to solve the Sellmeier equation (Eq. 3) and get the nonlinear refractive index
n (X) = 1 + £
^ X - B
j J
(9)
where Aj and Bj are coefficient values that form results from a relatively simple physical model.
Photoluminescence spectra. The photol
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.