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Eu3+ doped YNbO4 phosphor properties for fluorescence thermometry
Radiation Measurements xxx (2013) 1e4
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry Lj.R. Ða canin a, *, M.D. Drami canin b, S.R. Luki c-Petrovi c a, D.M. Petrovi c a, M.G. Nikoli cb a b
University of Novi Sad, Department of Physics, Trg Dositeja Obradovica 4, 21000 Novi Sad, Serbia Vinca Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia
h i g h l i g h t s < Efficient YNbO4:1at%Eu3þ phosphor was synthesized by a simple solid-state reaction. < Photoluminescence emission spectra were studied in the temperature range 303e803 K. < Intensity ratio of 5D1 / 7F1 and 5D0 / 7F1 Eu3þ ion transitions may be used for temperature measurements. < The temperature sensitivity is about 3.5 103 K1 in the region around 700 K.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 October 2012 Received in revised form 6 January 2013 Accepted 18 January 2013
We prepared an efficient YNbO4:Eu3þ phosphor using a simple solid-state reaction method and examined its photoluminescent properties in order to investigate the possibility for its usage in phosphor thermometry. Photoluminescence measurements were performed in the temperature range 303e803 K, and the fluorescence intensity ratio (FIR) of the paired emissions lines of Eu3þ (5D1 / 7F1 and 5D0 / 7F1 transitions) was studied as a function of temperature. The sample crystalline structure is confirmed by XRD measurements. The material is proved to have a good potential for the development of thermographic phosphors. It exhibits maximum temperature sensitivity of approximately 3.5 103 K1 in the temperature region around 700 K. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Yttrium niobate Phosphor thermometry Eu3þ
1. Introduction Phosphors are defined as materials that absorb energy and subsequently emit it as UV, visible or IR light. They are composed of an inorganic host doped with activator ions, typically a transition metal or rare earth (RE). In particular RE-doped phosphors are important materials having major applications in artificial lights, Xray medical radiography, display devices and high-power solidstate lasers (Blasse and Grabmaier, 1994). Phosphor thermometry is a non-contact technique that uses optical signals to remotely measure the temperature. Phosphors specifically designed for phosphor thermometry are called thermographic phosphors (TGPs). Unlike conventional methods in measuring temperature (thermocouples, thermistors, thermal paints), TGPs are resistant to oxidation in high-temperature environments and do not react with harsh chemicals. Emission characteristics of TGPs change with temperature, which variations depend on the type of RE impurity and the host. The phosphor
* Corresponding author. Tel.: þ381 214852814; fax: þ381 21459367. E-mail address: [email protected] (Lj.R. Ða canin).
thermometry is based on two major methods: the decay measurements or the intensity ratio measurements. The latter has been widely accepted since it eliminates a number of errors coming from fluctuations of the excitation light source, temperature changes of excitation bands and non-uniform dopant concentrations (Khalid and Kontis, 2008), and has been used in this study. Yttrium niobate (YNbO4) phosphor is an efficient X-ray phosphor generally used in X-ray medical imaging, as well as in computed radiography, tomography and fluoroscopy (Blasse and Grabmaier, 1994; Curry et al., 1990; Sonoda et al., 1983). The blue light emission from yttrium niobate phosphor under X-ray excitation is associated with NbO34 groups of host crystalline lattice (Blasse and Brill, 1968). The luminescence at longer wavelengths can be obtained when yttrium niobate is doped with other rareearth ions that partly replace yttrium ions in the host lattice. Thus, Eu3þ centers produce characteristic red luminescence. Yttrium niobate phosphor is usually synthesized by solid state reaction method, using a ball mill to grind precursors for tens of hours (Karsu et al., 2011; Nazarov et al., 2010). Here we prepared singlephase Eu3þ-doped YNbO4 powder using faster, simpler and energetically more efficient solid-state reaction method. Although there are publications on Eu3þ-doped yttrium niobate (Chenglu et al.,
1350-4487/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Lj.R. Ðacanin et al. / Radiation Measurements xxx (2013) 1e4
2
2012; Massabni et al., 1998; Nazarov et al., 2010), to the best of our knowledge, there are no publications on possible thermometric properties of this phosphor. In this research we investigated the possibility for YNbO4:Eu3þ usage in phosphor thermometry by observing temperature changes of trivalent europium transitions from 5D0 and 5D1 energy levels to the ground state. The temperature dependence of emission intensities is presented and discussed. 2. Experimental YNbO4:Eu3þ (1 at%) sample was synthesized using a simple solid-state procedure. Precursors powders were mixed by making a slurry in methanol, pre-sintered at 800 C for 2 h, then powderized in a mortar, sintered at 1300 C for 8 h, and finally cooled down slowly to room temperature. Starting components were Y2O3 (Aldrich, 99.99%) and Nb2O5 (Alfa Aesar, 99.5%), the dopant precursor was Eu2O3 (Aldrich, 99.99%), while Na2SO4 (MERCK-Alkaloid, p.a.) was added as a flux to promote a solid state reaction by accelerating the kinetics for the compound formation due to the increased diffusion coefficients. Phase purity of the sample was confirmed by X-ray diffraction measurements performed with Philips PW 1050 instrument, using Ni filtered Cu Ka1,2 radiation. Diffraction data was recorded in a 2q range from 10B to 80B counting for 10 s in 0.02B steps. The photoluminescence (PL) spectra were acquired using a Fluorolog-3 Model FL3-221 spectrofluorometer system (Horiba Jobin-Yvon), with a 450 W Xenon lamp and R928P photomultiplier tube. Excitation and emission monochromators were a double grating design, with a dispersion of 2.1 nm/mm (1200 grooves/ mm). The sample was placed into a thermostabilized oven and connected to spectrofluorometer by an optical wave-guide. This allows precise heating and photoluminescence measurements at different temperatures. Temperature was gradually increased in steps of 50 K from room temperature to 803 K. PL measurements were performed on pellets prepared from powder under the load of 5 105 kg/m2. 3. Results and discussion XRD spectrum of YNbO4:Eu3þ powder, presented in Fig. 1, confirmed successful formation of the monoclinic M-YNbO4 fergusonite-b crystal structure. The most intense peaks are indexed
Fig. 1. XRD spectrum of YNbO4:1at%Eu3þ sample.
according to the JCPDS 23-1486 diffraction data. In this structure, Y3þ ions are surrounded by 8-coordinated oxygen atoms forming a distorted cube (Arellano et al., 2010). Since Eu3þ ions partly replace Y3þ in this structure, we can say that it occupies a site without a centre of symmetry. The fluorescence intensity ratio (FIR) method is based on the intensity ratio between two emission lines in the PL spectrum. Applying this method reduces the influence of measurement conditions and therefore improves the measurement sensitivity. Two emission lines are considered appropriate for FIR method if their intensities show different responses to temperature, and their intensities are strong enough to avoid optical noise (Khalid and Kontis, 2008). A special case of the FIR measurement technique uses the fluorescence intensities from two closely spaced energy levels of RE ion, which are thermally coupled and are assumed to be in thermodynamical quasi-equilibrium state. In ideal case, the intensity of one of the emission lines is independent of temperature (internal reference); in this way a calibration between the ratios of emissions will be indicative of temperature. However, in rare-earth based thermophosphors this ideal temperature independent emissions do not exist because of energy transfer between levels. Anyhow, small energy gap between these two levels allows the upper level to be populated from the lower level by thermal excitation. Fig. 2 shows a diagram of three energy levels of the RE ion, as well as Eu3þ ion levels that this method can be applied to. Relative population between two levels, R, follows Boltzmann-type population distribution given by (Heyes, 2004):
R ¼
I31 E ¼ Cexp 32 ; I21 kT
(1)
where k is the Boltzmann constant, and E32 is the energy gap between two excited levels. The rate at which the ratio R changes with the temperature represents the sensor sensitivity, S (Haro-Gonzales et al., 2011):
dR E S ¼ ¼ R 322 : dT kT
(2)
From eqs. (1) and (2) it is clear that sensitivity is larger with larger energy difference E32 and pre-exponential factor C. However, in cases when energy difference is too large, the population of
Fig. 2. Energy levels diagram of the RE (Eu3þ) ion.
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Lj.R. Ðacanin et al. / Radiation Measurements xxx (2013) 1e4
Fig. 3. Emission spectra of YNbO4:1at%Eu3þ sample over the temperature range 303e 803 K.
higher energy level is not possible by thermalization. Then the method is not applicable since the levels are not thermally coupled. Fig. 3 shows the YNbO4:1at%Eu3þ luminescence spectra measured at different temperatures in the range of (303e803) K. The luminescence was excited at 395 nm. Six emission bands, with maxima at 539, 554, 595, 613, 657 and 705 nm correspond to 5 D1 / 7FJ (J ¼ 1, 2) and 5D0 / 7FJ (J ¼ 1, 2, 3, 4) transitions, respectively. The 5D0 / 7F2 electric dipole transition is the most dominant, as it usually occurs when the Eu3þ ion occupies a site without center of symmetry (Blasse and Grabmaier, 1994). In Fig. 4 the intensity-temperature dependencies of 5D1 / 7F1 and 5D0 / 7F1 transitions are given. With the temperature increase, the upper 5D1 level becomes more populated by thermal population from 5D0 level. Therefore, the fluorescence from level 5D1 gradually increases on the expense of the lower level emission. After a certain point, the emission intensities of both levels decrease as a consequence of thermal quenching. Considering this, 5 D1 / 7F1 (emission line at 539 nm) and 5D0 / 7F1 (emission line at 595 nm) transitions were chosen as suitable for FIR method. We found that intensity ratio of these emission lines depends strongly
3
Fig. 5. FIR of the 5D1 / 7F1 and 5D0 / 7F1 transitions as a function of temperature. The solid line is the experimental data fit according to eq. (1).
Fig. 6. Calculated sensor sensitivity as a function of temperature.
on temperature, and the dependence is given Fig. 5. Obtained experimental data were fitted according to eq. (1) and the values of C ¼ 19.98 and E ¼ 1619.99 cm1 were found. Value calculated for the energy gap is in good agreement with the energy levels of Eu3þ ions (Dieke, 1968). Sensor temperature sensitivity is obtained as first derivate of measured fluorescence intensity ratio (eq. (2)) and the curve is presented in Fig. 6. Sample exhibits significant temperature sensitivity, having the maximum sensitivity of about 3.5 103 K1 in the region around 700 K. 4. Conclusions
Fig. 4. Intensity-temperature dependencies of the transitions.
5
D1 /
7
F1 and
5
D0 /
7
F1
YNbO4:1at%Eu3þ phosphor powder was successfully synthesized using a simple solid-state preparation method. Prepared sample exhibits intense red emission, characteristic for electronic transitions within trivalent europium ions. FIR method was applied in order to examine the possibility of using this material as thermographic phosphor. PL measurements recorded from room temperature up to 803 K have shown that YNbO4:1at%Eu3þ possesses the maximum sensitivity of approximately 3.5 103 K1 at about 700 K, indicating this material to be a good temperature sensor within the studied temperature range.
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Lj.R. Ðacanin et al. / Radiation Measurements xxx (2013) 1e4
4
Acknowledgment Authors acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia within the Project No. OI171022 and Project No. III45020. References Arellano, I., Nazarov, M., Byeon, C.C., Popovici, E.-J., Kim, H., Kang, H.C., Noh, D.Y., 2010. Luminescence and structural properties of Y(Ta, Nb)O4:Eu3þ, Tb3þ phosphors. Mat. Chem. Phys. 119, 48e51. Blasse, G., Bril, A., 1968. Photoluminescent efficiency of phosphors with electronic transitions in localized centres. J. Electrochem. Soc. 115, 1067e1075. Blasse, G., Grabmaier, B.C., 1994. Luminescent Materials. Springer-Verlag, Berlin. Chenglu, L., Fang, W., Zhiqiang, Z., Peiyun, J., 2012. Molten salt synthesis and luminescent properties of YNbO4: Eu nanophosphors. Adv. Sci. Lett. 10, 274e278. Curry III, T.S., Dowdey, J.E., Murry Jr., R.C., 1990. Christensen’s Physics of Diagnostic Radiology, fourth ed. Lea and Febiger, Philadelphia.
Dieke, G.H., 1968. Spectra and Energy Levels of Rare Earth Ions in Crystals. Interscience Publishers, New York. Haro-Gonzales, P., Martin, I.R., Martin, L.L., Leon-Luis, S.F., Perez-Rodrigez, C., Lavin, V., 2011. Characterization of Er3þ and Nd3þ doped strontium barium niobate glass ceramics as temperature sensors. Opt. Mat 33, 742e745. Heyes, A.L., 2004. Thermographic phosphor thermometry for gas turbines. In: Sieverding, C.H., Brouckaert, J.-F. (Eds.), Advanced Measurement Techniques for Aeroengines and Stationary Gas Turbines. Von Karmen Institute for fluid dynamics, Rhode-St-Genèse. Karsu, E.C., Popovici, E.J., Ege, A., Morar, M., Indrea, E., Karali, T., Can, N., 2011. Luminescence study of some yttrium tantalate-based phosphors. J. Lumin. 131, 1052e1057. Khalid, A.H., Kontis, K., 2008. Thermographic phosphors for high temperature measurements: principles, current state of the art and recent applications. Sensors 8, 5673e5744. Massabni, A.M.G., Mantandon, G.J.M., Couto dos Santos, M.A., 1998. Synthesis and luminescence spectroscopy of YNbO4 doped with Eu(III). Mat. Res. 1, 1e4. Nazarov, M., Kim, Y.J., Lee, E.Y., Min, K.-I., Jeong, M.S., Lee, S.W., Noh, D.Y., 2010. Luminescence and Raman Studies of YNbO4 phosphors doped by Eu3þ, Ga3þ and Al3þ. J. App. Phys. 107. 103104e103104-6. Sonoda, M., Takano, M., Miyahara, J., Kato, H., 1983. Computed radiography utilizing scanning laser stimulated luminescence. Radiology 148, 833e838.
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry Lj.R. Ða canin a, *, M.D. Drami canin b, S.R. Luki c-Petrovi c a, D.M. Petrovi c a, M.G. Nikoli cb a b
University of Novi Sad, Department of Physics, Trg Dositeja Obradovica 4, 21000 Novi Sad, Serbia Vinca Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia
h i g h l i g h t s < Efficient YNbO4:1at%Eu3þ phosphor was synthesized by a simple solid-state reaction. < Photoluminescence emission spectra were studied in the temperature range 303e803 K. < Intensity ratio of 5D1 / 7F1 and 5D0 / 7F1 Eu3þ ion transitions may be used for temperature measurements. < The temperature sensitivity is about 3.5 103 K1 in the region around 700 K.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 October 2012 Received in revised form 6 January 2013 Accepted 18 January 2013
We prepared an efficient YNbO4:Eu3þ phosphor using a simple solid-state reaction method and examined its photoluminescent properties in order to investigate the possibility for its usage in phosphor thermometry. Photoluminescence measurements were performed in the temperature range 303e803 K, and the fluorescence intensity ratio (FIR) of the paired emissions lines of Eu3þ (5D1 / 7F1 and 5D0 / 7F1 transitions) was studied as a function of temperature. The sample crystalline structure is confirmed by XRD measurements. The material is proved to have a good potential for the development of thermographic phosphors. It exhibits maximum temperature sensitivity of approximately 3.5 103 K1 in the temperature region around 700 K. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Yttrium niobate Phosphor thermometry Eu3þ
1. Introduction Phosphors are defined as materials that absorb energy and subsequently emit it as UV, visible or IR light. They are composed of an inorganic host doped with activator ions, typically a transition metal or rare earth (RE). In particular RE-doped phosphors are important materials having major applications in artificial lights, Xray medical radiography, display devices and high-power solidstate lasers (Blasse and Grabmaier, 1994). Phosphor thermometry is a non-contact technique that uses optical signals to remotely measure the temperature. Phosphors specifically designed for phosphor thermometry are called thermographic phosphors (TGPs). Unlike conventional methods in measuring temperature (thermocouples, thermistors, thermal paints), TGPs are resistant to oxidation in high-temperature environments and do not react with harsh chemicals. Emission characteristics of TGPs change with temperature, which variations depend on the type of RE impurity and the host. The phosphor
* Corresponding author. Tel.: þ381 214852814; fax: þ381 21459367. E-mail address: [email protected] (Lj.R. Ða canin).
thermometry is based on two major methods: the decay measurements or the intensity ratio measurements. The latter has been widely accepted since it eliminates a number of errors coming from fluctuations of the excitation light source, temperature changes of excitation bands and non-uniform dopant concentrations (Khalid and Kontis, 2008), and has been used in this study. Yttrium niobate (YNbO4) phosphor is an efficient X-ray phosphor generally used in X-ray medical imaging, as well as in computed radiography, tomography and fluoroscopy (Blasse and Grabmaier, 1994; Curry et al., 1990; Sonoda et al., 1983). The blue light emission from yttrium niobate phosphor under X-ray excitation is associated with NbO34 groups of host crystalline lattice (Blasse and Brill, 1968). The luminescence at longer wavelengths can be obtained when yttrium niobate is doped with other rareearth ions that partly replace yttrium ions in the host lattice. Thus, Eu3þ centers produce characteristic red luminescence. Yttrium niobate phosphor is usually synthesized by solid state reaction method, using a ball mill to grind precursors for tens of hours (Karsu et al., 2011; Nazarov et al., 2010). Here we prepared singlephase Eu3þ-doped YNbO4 powder using faster, simpler and energetically more efficient solid-state reaction method. Although there are publications on Eu3þ-doped yttrium niobate (Chenglu et al.,
1350-4487/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Lj.R. Ðacanin et al. / Radiation Measurements xxx (2013) 1e4
2
2012; Massabni et al., 1998; Nazarov et al., 2010), to the best of our knowledge, there are no publications on possible thermometric properties of this phosphor. In this research we investigated the possibility for YNbO4:Eu3þ usage in phosphor thermometry by observing temperature changes of trivalent europium transitions from 5D0 and 5D1 energy levels to the ground state. The temperature dependence of emission intensities is presented and discussed. 2. Experimental YNbO4:Eu3þ (1 at%) sample was synthesized using a simple solid-state procedure. Precursors powders were mixed by making a slurry in methanol, pre-sintered at 800 C for 2 h, then powderized in a mortar, sintered at 1300 C for 8 h, and finally cooled down slowly to room temperature. Starting components were Y2O3 (Aldrich, 99.99%) and Nb2O5 (Alfa Aesar, 99.5%), the dopant precursor was Eu2O3 (Aldrich, 99.99%), while Na2SO4 (MERCK-Alkaloid, p.a.) was added as a flux to promote a solid state reaction by accelerating the kinetics for the compound formation due to the increased diffusion coefficients. Phase purity of the sample was confirmed by X-ray diffraction measurements performed with Philips PW 1050 instrument, using Ni filtered Cu Ka1,2 radiation. Diffraction data was recorded in a 2q range from 10B to 80B counting for 10 s in 0.02B steps. The photoluminescence (PL) spectra were acquired using a Fluorolog-3 Model FL3-221 spectrofluorometer system (Horiba Jobin-Yvon), with a 450 W Xenon lamp and R928P photomultiplier tube. Excitation and emission monochromators were a double grating design, with a dispersion of 2.1 nm/mm (1200 grooves/ mm). The sample was placed into a thermostabilized oven and connected to spectrofluorometer by an optical wave-guide. This allows precise heating and photoluminescence measurements at different temperatures. Temperature was gradually increased in steps of 50 K from room temperature to 803 K. PL measurements were performed on pellets prepared from powder under the load of 5 105 kg/m2. 3. Results and discussion XRD spectrum of YNbO4:Eu3þ powder, presented in Fig. 1, confirmed successful formation of the monoclinic M-YNbO4 fergusonite-b crystal structure. The most intense peaks are indexed
Fig. 1. XRD spectrum of YNbO4:1at%Eu3þ sample.
according to the JCPDS 23-1486 diffraction data. In this structure, Y3þ ions are surrounded by 8-coordinated oxygen atoms forming a distorted cube (Arellano et al., 2010). Since Eu3þ ions partly replace Y3þ in this structure, we can say that it occupies a site without a centre of symmetry. The fluorescence intensity ratio (FIR) method is based on the intensity ratio between two emission lines in the PL spectrum. Applying this method reduces the influence of measurement conditions and therefore improves the measurement sensitivity. Two emission lines are considered appropriate for FIR method if their intensities show different responses to temperature, and their intensities are strong enough to avoid optical noise (Khalid and Kontis, 2008). A special case of the FIR measurement technique uses the fluorescence intensities from two closely spaced energy levels of RE ion, which are thermally coupled and are assumed to be in thermodynamical quasi-equilibrium state. In ideal case, the intensity of one of the emission lines is independent of temperature (internal reference); in this way a calibration between the ratios of emissions will be indicative of temperature. However, in rare-earth based thermophosphors this ideal temperature independent emissions do not exist because of energy transfer between levels. Anyhow, small energy gap between these two levels allows the upper level to be populated from the lower level by thermal excitation. Fig. 2 shows a diagram of three energy levels of the RE ion, as well as Eu3þ ion levels that this method can be applied to. Relative population between two levels, R, follows Boltzmann-type population distribution given by (Heyes, 2004):
R ¼
I31 E ¼ Cexp 32 ; I21 kT
(1)
where k is the Boltzmann constant, and E32 is the energy gap between two excited levels. The rate at which the ratio R changes with the temperature represents the sensor sensitivity, S (Haro-Gonzales et al., 2011):
dR E S ¼ ¼ R 322 : dT kT
(2)
From eqs. (1) and (2) it is clear that sensitivity is larger with larger energy difference E32 and pre-exponential factor C. However, in cases when energy difference is too large, the population of
Fig. 2. Energy levels diagram of the RE (Eu3þ) ion.
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Lj.R. Ðacanin et al. / Radiation Measurements xxx (2013) 1e4
Fig. 3. Emission spectra of YNbO4:1at%Eu3þ sample over the temperature range 303e 803 K.
higher energy level is not possible by thermalization. Then the method is not applicable since the levels are not thermally coupled. Fig. 3 shows the YNbO4:1at%Eu3þ luminescence spectra measured at different temperatures in the range of (303e803) K. The luminescence was excited at 395 nm. Six emission bands, with maxima at 539, 554, 595, 613, 657 and 705 nm correspond to 5 D1 / 7FJ (J ¼ 1, 2) and 5D0 / 7FJ (J ¼ 1, 2, 3, 4) transitions, respectively. The 5D0 / 7F2 electric dipole transition is the most dominant, as it usually occurs when the Eu3þ ion occupies a site without center of symmetry (Blasse and Grabmaier, 1994). In Fig. 4 the intensity-temperature dependencies of 5D1 / 7F1 and 5D0 / 7F1 transitions are given. With the temperature increase, the upper 5D1 level becomes more populated by thermal population from 5D0 level. Therefore, the fluorescence from level 5D1 gradually increases on the expense of the lower level emission. After a certain point, the emission intensities of both levels decrease as a consequence of thermal quenching. Considering this, 5 D1 / 7F1 (emission line at 539 nm) and 5D0 / 7F1 (emission line at 595 nm) transitions were chosen as suitable for FIR method. We found that intensity ratio of these emission lines depends strongly
3
Fig. 5. FIR of the 5D1 / 7F1 and 5D0 / 7F1 transitions as a function of temperature. The solid line is the experimental data fit according to eq. (1).
Fig. 6. Calculated sensor sensitivity as a function of temperature.
on temperature, and the dependence is given Fig. 5. Obtained experimental data were fitted according to eq. (1) and the values of C ¼ 19.98 and E ¼ 1619.99 cm1 were found. Value calculated for the energy gap is in good agreement with the energy levels of Eu3þ ions (Dieke, 1968). Sensor temperature sensitivity is obtained as first derivate of measured fluorescence intensity ratio (eq. (2)) and the curve is presented in Fig. 6. Sample exhibits significant temperature sensitivity, having the maximum sensitivity of about 3.5 103 K1 in the region around 700 K. 4. Conclusions
Fig. 4. Intensity-temperature dependencies of the transitions.
5
D1 /
7
F1 and
5
D0 /
7
F1
YNbO4:1at%Eu3þ phosphor powder was successfully synthesized using a simple solid-state preparation method. Prepared sample exhibits intense red emission, characteristic for electronic transitions within trivalent europium ions. FIR method was applied in order to examine the possibility of using this material as thermographic phosphor. PL measurements recorded from room temperature up to 803 K have shown that YNbO4:1at%Eu3þ possesses the maximum sensitivity of approximately 3.5 103 K1 at about 700 K, indicating this material to be a good temperature sensor within the studied temperature range.
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038
Lj.R. Ðacanin et al. / Radiation Measurements xxx (2013) 1e4
4
Acknowledgment Authors acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia within the Project No. OI171022 and Project No. III45020. References Arellano, I., Nazarov, M., Byeon, C.C., Popovici, E.-J., Kim, H., Kang, H.C., Noh, D.Y., 2010. Luminescence and structural properties of Y(Ta, Nb)O4:Eu3þ, Tb3þ phosphors. Mat. Chem. Phys. 119, 48e51. Blasse, G., Bril, A., 1968. Photoluminescent efficiency of phosphors with electronic transitions in localized centres. J. Electrochem. Soc. 115, 1067e1075. Blasse, G., Grabmaier, B.C., 1994. Luminescent Materials. Springer-Verlag, Berlin. Chenglu, L., Fang, W., Zhiqiang, Z., Peiyun, J., 2012. Molten salt synthesis and luminescent properties of YNbO4: Eu nanophosphors. Adv. Sci. Lett. 10, 274e278. Curry III, T.S., Dowdey, J.E., Murry Jr., R.C., 1990. Christensen’s Physics of Diagnostic Radiology, fourth ed. Lea and Febiger, Philadelphia.
Dieke, G.H., 1968. Spectra and Energy Levels of Rare Earth Ions in Crystals. Interscience Publishers, New York. Haro-Gonzales, P., Martin, I.R., Martin, L.L., Leon-Luis, S.F., Perez-Rodrigez, C., Lavin, V., 2011. Characterization of Er3þ and Nd3þ doped strontium barium niobate glass ceramics as temperature sensors. Opt. Mat 33, 742e745. Heyes, A.L., 2004. Thermographic phosphor thermometry for gas turbines. In: Sieverding, C.H., Brouckaert, J.-F. (Eds.), Advanced Measurement Techniques for Aeroengines and Stationary Gas Turbines. Von Karmen Institute for fluid dynamics, Rhode-St-Genèse. Karsu, E.C., Popovici, E.J., Ege, A., Morar, M., Indrea, E., Karali, T., Can, N., 2011. Luminescence study of some yttrium tantalate-based phosphors. J. Lumin. 131, 1052e1057. Khalid, A.H., Kontis, K., 2008. Thermographic phosphors for high temperature measurements: principles, current state of the art and recent applications. Sensors 8, 5673e5744. Massabni, A.M.G., Mantandon, G.J.M., Couto dos Santos, M.A., 1998. Synthesis and luminescence spectroscopy of YNbO4 doped with Eu(III). Mat. Res. 1, 1e4. Nazarov, M., Kim, Y.J., Lee, E.Y., Min, K.-I., Jeong, M.S., Lee, S.W., Noh, D.Y., 2010. Luminescence and Raman Studies of YNbO4 phosphors doped by Eu3þ, Ga3þ and Al3þ. J. App. Phys. 107. 103104e103104-6. Sonoda, M., Takano, M., Miyahara, J., Kato, H., 1983. Computed radiography utilizing scanning laser stimulated luminescence. Radiology 148, 833e838.
Please cite this article in press as: Ðacanin, L.R., et al., Eu3þ doped YNbO4 phosphor properties for fluorescence thermometry, Radiation Measurements (2013), http://dx.doi.org/10.1016/j.radmeas.2013.01.038