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Научни трудове на Съюза на учените в България-Пловдив. Серия В. Техника и технологии, естествен ии хуманитарни науки, том XVI., Съюз на учените сесия "Международна конференция на младите учени" 13-15 юни 2013. Scientific research of the Union of Scientists in Bulgaria-Plovdiv, series C. Natural Sciences and Humanities, Vol. XVI, ISSN 1311-9192, Union of Scientists, International Conference of Young Scientists, 13 - 15 June 2013, Plovdiv.
Dependence of the optical properties on the composition of ZnO-P2O5-B2O5 materials doped with Sm
I.kostova*, Т. Pashova, G. Patronov, D. Tonchev, Т. Eftimov University of Plovdiv „Paisii Hilendarski", 24 Tsar Asen St. 4000 Plovdiv Bulgaria, e-mail: irena_k87@abv.bg
Abstract.
In recent years, there has been considerable interest in the synthesis and photoluminescence of rare earths doped new inorganic materials (borates, phosphates, borophosphates, etc.) due to their potential applications in laser technology, optical electronics, eco-technology and other fields.
This study presents the synthesis and determination of the optical properties of Sm: ZnO-P2O5-B2O3 materials. Several materials were synthesized: one sample in the in the proportion ZnO(72.31)-P2O5(9.69)-B2O3(18) and four samples of composition ZnO(72.31-x)-P2O5(9.69)-B203(18.00)-Sm203(x), where x = 0.25; 0.5; 0.75; 1.00 mol%. After reprocessing, all samples were subjected to analysis by photoluminescence excitation radiation sources with different wavelengths - 255, 370, 395, 425 and 450 nm.
Photoluminescence analysis shows that the most effective source of excitation for samarium-doped samples is the 395 nm radiation source. In addition, the emission spectra of samples at particular wavelength also exhibit the presence of ZnO in the ZnO-P2O5-B2O3 materials.
Introduction
This study presents the synthesis and determination of the optical properties of Sm: ZnO-P2O5-B2O3 materials. Several materials were synthesized: one sample in the proportion ZnO(72.3l)-P2O5(9.69)-B2O3(18) and four samples of composition Zn0(72.31-x)-P205(9.69)-B203(18.00)-Sm2O3(x), where x = 0.25; 0.5; 0.75; 1.00 mol%.
The synthesis of the samples was performed at 950 0C in a muffle furnace for three hours. After pouring and cooling, the compositions were subjected to annealing at 250 0C for two hours. The obtained samples are transparent glass materials.
After reprocessing, all samples were subjected to analysis by photoluminescence excitation radiation sources with different wavelengths - 255, 370, 395, 425 and 450 nm. Absorption spectra were measured also.
Experimental
Synthesis
The composition of the materials was selected in accordance with the specialized literature. The proportion of the components was not found in the available references [1, 2].
Five samples were synthesized by the system ZnO-P2O5-B2O3 - one non-doped and the remaining four doped with different concentration of Sm. The materials' composition was selected based on our previous study of the optical properties of such materials [3, 4].
The following reagents used for the synthesis of the compounds: ZnO, P2O5, B2O3 and Sm2O3. The ratio between above-mentioned raw materials is given in Table 1.
Table 1
Content of the ZnO-P2O 5-B 2O 5 materials
№ ZnO, mol% P2O5, mol% B2O3, mol% Sm2O3, mol%
1 72.31 9.69 18.00 -
2 72.06 9.69 18.00 0.25
3 71.81 9.69 18.00 0.50
4 71.56 9.69 18.00 0.75
5 71.31 9.69 18.00 1.00
The synthesis was carried out by weighing, mixing and homogenization of reagents with subsequent melting and melts quenching. The synthesis was carried out in a muffle furnace at a rate of temperature increasing was 30 0C/min. After reaching 950 0C the mixture was in the melting state for three hours. Then, the melt was poured on graphite plate and annealed at 250 0C for two hours. By changing the content of the alloying components, varying degrees of transparency of the synthesized materials is achieved, whereby it is increase enhances turbidity (Fig. 1).
Fig.1 Photograph of samples with different content of samarium
The photograph shows that the high content of Sm2O3 changes the appearance of the samples due to occurring structural changes. These changes can be seen from the absorption spectra (figure 6).
Preparation of samples
The resulting glass samples were in the form of droplets with a diameter about 5 mm. For the purposes of the optical measurement, samples were prepared by cutting and polishing part of the surface to obtain two parallel and one perpendicular side. Polishing is done with polishing machine (Buhler), by consecutively using sandpaper of different roughness - 30^m, 16^m, 9^m.
Optical measurements
The set-up consists of a light source, a sample and a detection system. The light source is a combination of a Deuterium and a Halogen lamp, providing a spectrum with the 200 - 2500 nm range for transmission and absorption measurements and, semiconductor light emitting diodes (LEDs), emitting at 370 nm, 395 nm, 425 nm and 450 nm to pump directly the sample under study for fluorescence measurements.
Results and discussion
Photoluminescent analysis
Fig. 2 presents a comparison of the fluorescence emission spectra of the non-doped glass matrix and the pure ZnO. The graph shows that the fluorescence in the sample is entirely due to the zinc oxide.
Fig. 2 Fluorescence spectra of ZnO-P O -B O and ZnO, for a 255 nm excitation
It is seen from the performed experiments that this spectrum manifests itself in the UV spectral range under 350 nm. The effect observed with the Sm doped glass samples is a broadening of the pedestal of their first fluorescence peak. Studies in the range above 350 nm reveal that ZnO fluorescence is weak and merges with the detector's noise, which is observed in the spectrum from Fig. 3.
Fig.3 Fluorescence spectra of ZnO-P O -B O for 370 nm excitation
Fig. 4 presents the emission fluorescence spectra of Zn-B phosphate glasses doped with 0.25% Sm for different excitation sources.
Fig. 4 Fluorescence spectra of Sm: ZnO-P2O5-B2O3, for 0.25 mol% of Sm
The plots show that the most efficient LED for pumping the glasses is the one at 395 nm. Except for the 370 nm LED, the increase of the pump wavelength a decrease of the fluorescence intensity is observed. In all of the spectra, we observe three peaks at correspondingly 560, 600 and 645 nm. In addition, a fourth peak at 704 nm is observed which considerably weaker than the former. These peaks are characteristic for Sm3+ [5].
Integration over the whole fluorescence spectrum allows the ratio of fluorescence to excitation to be calculated and plotted for every source and is shown in Fig. 5.
Fig. 5 Integral representation of the total fluorescence for the different excitation
wavelengths
Fig. 5 shows that the highest excitation efficiency is for 395 nm. Another important dependence is that the increase of Sm concentration in the samples, the fluorescence intensity decreases. This is a reason to consider that 0.75% Sm^ is the optimum contents for this matrix [6].
Absorption spectra
The experimental data are shown graphically in Fig. 6. As is seen for the samples
containing 0.25, 0.5 and 0.75 mol% Sm exhibit a good optical absorption in the 250 nm to 450 nm range. An exception is the spectrum of the sample containing 1 mol% Sm, which is caused by its turbidity.
Fig. 6 Absorption spectra of sample №2 (0.25% Sm2O), №3 (0.50% Sm2O), №4 (0.75% Sm2O) and №5 (1.00% Sm2O)
Conclusions
The performed experiments and analysis allow the following conclusions to be formulated:
1. Fluorescence in the glass matrix of ZnO-P2O5-B2O5 is caused by ZnO.
2. The glass matrix shifts the fluorescence peak of ZnO Xem= 490 nm, by 4-5 nm.
3. The intensity of fluorescence decreases with the increase of the content of Sm2O3.
4. The most efficient pumping source was the LED at 395 nm.
Acknowledgments
This research was funded by the "Scientific Research" fund at Plovdiv University, Grant № NI 13 HF 006.
Reference
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3. T. Pashova, I. Kostova, T. Eftimov, D. Tonchev, G. Patronov, Scientific works of University of Plovdiv Paisii Hilendarski ,37(4), 2012, 11-18.
4. T. Pashova, I. Kostova, T. Eftimov, D. Tonchev, G. Patronov, Journal of the Technical University, 18, 2012, 137-142.
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