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5Condensed Matter and Interphases (Kondensirovannye sredy i mezhfaznye granitsy)
Original article
DOI: https://doi.org/10.17308/kcmf.2020.22/2834 ISSN 1606-867X
Received 19 February 2020 elSSN 2687-0711
Accepted 15 April 2020 Published online 25 June 2020
The Study of the Luminescence of Solid Solutions Based on Yttrium Fluoride Doped with Ytterbium and Europium for Photonics
© 2020 S. V. Kuznetsov®", A. S. Nizamutdinovb, E. I. Madirovb, V. A. Konyushkina, A. N. Nakladova, V. V. Voronova, A. D. Yapryntsev0, V. K. Ivanovo V. V. Semashkob, P. P. Fedorova
aProkhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilov str., Moscow 119991, Russian Federation
bKazan Federal University,
18 Kremlyovskaya str., Kazan 420008, Russian Federation
cKurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, 31 Leninsky pr., Moscow, 119991 Russian Federation
Abstract
The majority of the global market for solar photovoltaic devices is based on silicon technology. It is very important to increase their efficiency through the use of luminescent coatings, including those converting radiation from the UV-blue region of the spectrum into the near-infrared range, where silicon absorbs radiation most efficiently (Stokes or down-conversion luminescence), or from the infrared region of the spectrum in the near-infrared range (up-conversion luminescence). The aim of this research was to synthesize and study the spectral-kinetic characteristics of single-phase solid solutions of Y1-;-yEuYbF3 and to determine the quantum yield of down-conversion luminescence. Using the method of high-temperature melting, single-phase samples of solid solutions of Y1-;-yEuYbF3 with orthorhombic system were synthesized. For the series of samples with different Eu3+/Yb3+ ratios, upon double doping with these ions, the formation of the corresponding solid solutions with a crystal lattice of the p-YF3 phase was confirmed. Their chemical composition was determined using the energy dispersion analysis, and it was established that it corresponds to the nominal one. It was shown that both Eu3+ and Yb3+ ions become luminescent upon excitation at wavelengths of 266 nm and 296 nm. This indicates these compounds as promising sensitisers of UV radiation. In this case, upon excitation at a wavelength of 266 nm, luminescence of Eu2+ ions was recorded. The maximum quantum yield values (2.2 %) of the ytterbium down-conversion luminescence in the near-infrared wavelength range upon excitation at a wavelength of 266 nm were recorded for YF3:Eu:Yb with the Eu3+:Yb3+ ratios of 0.1:10.0 and 0.05:5.00.
Keywords: rare earth fluorides, phosphors, solar panels, down-conversion luminescence. Funding: This study was supported by Russian Science Foundation grant No. 17-73-20352.
For citation: Kuznetsov S. V., Nizamutdinov A. S., Madirov E. I., Konyushkin V. A., Nakladov A. N., Voronov V. V., Yapryntsev A. D., Ivanov V. K., Semashko V. V., Fedorov P. P. The study of the luminescence of solid solutions based on yttrium fluoride doped with ytterbium and europium for photonics. Kondensirovannye sredy i mezhfaznye granitsy = Condensed Matter and Interphases. 2020; 22(2): 225-231. DOI: https://doi.org/10.17308/kcmf.2020.22/2834
El Sergey V. Kuznetsov, e-mail: kouznetzovsv@gmail.com
The content is available under Creative Commons Attribution 4.0 License.
1. Introduction
The majority of the global market for solar photovoltaic devices is based on silicon technology. According to a report by the Fraunhofer Institute for Solar Energy (Fraunhofer ISE) in 2017, the widespread use of silicon is based on its availability and low cost of raw materials, the perfection of the technology for producing silicon of the required purity, and its non-toxicity to humans and the environment [1]. This is due to a significant simplification of the technology for purifying cheap silicon to an acceptable level [2]. From 2008 to 2017, there was a significant decrease in the cost of solar electricity from 3 US dollars / W to 0.3 US dollars / W [1]. It should be pointed out that failed solar panels can now be recycled as waste electronic components (e-waste). This strongly distinguishes them from new intensively developed organohalide materials with a perovskite structure of the RPbX type (R is an organic radical, X is Br or I, or their solid solution) [3-5]. It should be noted that most of these substances are less chemically stable and decompose over several years, and the recycling of heavy elements requires specific industries and significant investments.
One of the significant disadvantages of silicon is its low efficiency (less than 25 % even for the best samples [6,7]) of converting sunlight into electricity. In reality, the 22.5 % efficiency of solar energy conversion was achieved in devices produced at one of the largest silicon solar panel production plants located in Novocheboksarsk, Russia. There are various options for increasing the efficiency of silicon solar cells with multilayer structures, structures with different surface architecture types, and luminescent coatings [8, 9]. The photosensitivity spectrum and the maximum generation of electricity by silicon do not coincide with the spectrum of the Sun [6]. The maximum photosensitivity of silicon is in the range of 9001100 nm, which coincides with the spectral range of radiation of trivalent ytterbium ions. As a result, the efficiency of solar-silicon photovoltaic cells may be increased by using luminescent coatings.
Phosphors are suggested to be used for this purpose. They transform radiation from the UV-blue spectrum region (down-conversion luminescence) [6-11] or from the IR spectrum region (up-conversion luminescence) [12-14] to the near-infrared range due to a number of various
processes, including step transitions between the states of the corresponding ions, energy transfer, or cooperative processes. In this range, silicon absorbs radiation most efficiently [6].
The quantum yield of up-conversion luminescence in the visible range or near-infrared range upon excitation in the range of 1.5-2.0 ]m is very low [15-17], as two low-energy IR photons should be converted to one photon with higher energy in the near-infrared spectral range (NIR). The quantum efficiency of down-conversion luminescence is higher than that for up-conversion, because one ultraviolet or visible high-energy photon is converted to one or two NIR photons. The quantum efficiency of down-conversion luminescence in fluoride phosphors has been studied a lot for various matrices [18, 19], but the quantum yield, which is important for practical applications, has not been estimated.
The aim of this research was to synthesize and study the spectral-kinetic characteristics of solid solutions of Y, Eu Yb F_ and to determine the
1-x-y x y 3
quantum efficiency and quantum yield of down-conversion luminescence of ytterbium in the near-infrared range.
2. Experimental
Samples of yttrium fluoride-based solid solutions doped with ytterbium and europium were synthesized using the method of high-temperature melting. Yttrium fluoride, europium fluoride, and ytterbium fluoride had a purity degree of 99.99 % (LANHIT, Russia). The samples of Y1-x-yEuxYbyF3 solid solutions were synthesized in a vacuum oven at a temperature of 1155 °C. The mixture was placed in the vacuum oven in a graphite crucible and was gradually heated to 940 °C, then the vacuum pumping was turned off, a mixture of gases (CF4 and Ar) was introduced, and then it was smoothly heated to the melting temperature. The obtained melt was fluorinated and held at the process temperature for 30 minutes and then it was cooled to room temperature for 3 hours. The obtained samples were ground in an agate mortar.
All the samples were studied by X-ray diffraction analysis using a Bruker D8 Advanced diffractometer (CuKa radiation), their unit cell parameters were calculated in Powder 2.0 software (DO < 10). Their chemical composition was evaluated using a Carl
Zeiss NVision 40 scanning electron microscope with an energy dispersion spectrometer. Diffuse reflection spectra were recorded using a Lambda 950 Perkin Elmer spectrophotometer. The luminescence spectra were recorded on a Stellarnet EPP2000 spectrometer with a spectral resolution of 0.5 nm. A tunable wavelength laser system based on an Al2O3:Ti laser with second and third harmonic generators (LOTIS TII, 10 Hz, 10 ns) and a wavelength converter based on stimulated Raman scattering in gaseous H2 were used as an impulse excitation source. The luminescence kinetics were recorded using MDR-23 and MDR-3 monochromators, a photomultiplier FEU-100 was used as a photodetector in the visible region of the spectrum, and a photomultiplier FEU-62 was used in the IR region of the spectrum. The time scan of the luminescence kinetics signals was carried out by a BORDO digital oscilloscope with a bandwidth of 200 MHz and a dynamic range of 10 bits. The direct measurement of the quantum yield of Stokes luminescence was carried out using a Thorlabs IS200 integrating sphere and a SOLAR S100 spectrometer, calibrated using a wide-range temperature lamp TRSh-2850 and a yellow glass optical filter ZhS-16. When measuring the quantum yield of luminescence, we used the technique from [20], which involves correcting the spectral characteristics of the luminescence recording system and calibrating the optical system using light sources with a given intensity.
3. Results
The X-ray diffraction pattern of the Y0949Eu0.001Yb0.05F3 solution single-phase sample is provided in Fig. 1. It is typical for the whole
series of samples. The results of indexing in orthorhombic system (structural type b-YF3) are summarized in Table 1. The formation of a solid solution is confirmed by the absence of additional peaks compared to the corresponding JCPDS data and a change in the unit cell parameters of an undoped sample: YF3 (a = 6.353 A, b = 6.850 A, c = 4.393 A, JCPDS card # 74-0911).
The chemical composition was analysed based on energy dispersion analysis (Table 1), the results showed that the real composition corresponded to the nominal composition within the limits of the determination error of ± 0.5 mol%.
Luminescence of Eu 3+ ions was recorded in the YF3 samples doped with Eu and Yb ions, both upon excitation in the 399 nm region, characteristic of europium, and upon excitation in the UV region of the spectrum (296 and 266 nm). In the
Fig. 1. The X-ray diffraction pattern of the Yb0 F3 solid solution sample
Y Eu
0.949 0.001
Table 1. The unit cell parameters and results of energy dispersion analysis of the Y1-x-yEuYbyF3 solid solutions
Y, Eu Yb F3
1-x-y x y 3
Nominal composition Unit cell parameters, Â Composition according to EDX
a b c
YF3:Eu(0.05 MO..%):Yb(1.0 mqî.%) 6.365(1) 6.859(2) 4.3909(7) YF3:Eu(0.2 MO..%):Yb(2.1 mo^.%)
YF3:Eu(0.1 MO..%):Yb(5.0 mo..%) 6.345(2) 6.839(3) 4.384(1) YF3:Eu(0.4 MO..%):Yb(6.4 mo..%)
YF3:Eu(0.1 MO..%):Yb(1.0 mo..%) 6.342(2) 6.838(2) 4.3862(9) YF3:Eu(0.2 MO..%):Yb(1.9 mo..%)
YF3:Eu(0.05 MO..%):Yb(10.0 mo..%) 6.339(2) 6.834(2) 4.384(1) YF3:Eu(*):Yb(12.9 mqî.%)
YF3:Eu(0.05 MO..%):Yb(5.0 mo..%) 6.348(1) 6.842(2) 4.3859(9) YF3:Eu(0.1 MO..%):Yb(7.1 mo..%)
YF3:Eu(0.1 MO..%):Yb(10.0 mo..%) 6.3597(8) 6.851(1) 43891(6) YF3:Eu(0.1 MO..%):Yb(13.7 mo..%)
! - the europium concentration was not determined, since it is below the detection limit of the energy dispersion analysis.
corresponding spectra provided in Fig. 2, we can see the 5D0-7Fn (691, 650, 615, 590 nm), 5D1-7Fn (568, 556, 537, 5526 nm), 5D2-7Fn (511, 489, 464 nm) transitions, typical for Eu3+ [21]. Moreover, upon 266 nm excitation, a rather intense and wide luminescence band with a maximum in the region of430 nm was recorded, which may correspond to the 5d-4f interconfigurational transitions of Eu2+ ions [22]. It is important that the luminescence of Yb3+ ions was recorded only upon excitation at 266 nm and 296 nm (Fig. 2), and in the first case, it appeared to be more intense.
The luminescence kinetics of Eu3+ at a wavelength of 615 nm and Yb3+ at a wavelength of 1020 nm upon excitation at a wavelength of 266 nm for the YF3 matrix are provided in Fig. 3. The luminescence decay is non-exponential, for Yb3+ ions also with an increasing the concentration of Eu3+. In our case, the luminescence decay kinetics of Eu3+ ions can be divided into the fast component, which shortens with an increasing concentration of Yb3+, and the slow component, which becomes longer. Apparently, the fast component corresponds to the radiative lifetime of Eu3+ luminescence,
Fig. 2. The luminescence spectra of the YF3:Eu:Yb samples upon excitation at wavelengths of 399, 296, and 266 nm
Fig. 3. The luminescence kinetics of Eu3+ and Yb3+ ions in the YF3 samples upon excitation at a wavelength of 266 nm
which undergoes quenching due to energy transfer to Yb3+ ions. Meanwhile, the slow component is determined some kind of channel for refilling of the 5D0 state population of Eu3+ ions. To evaluate the luminescence lifetime the mean lifetime was used, which was calculated using formula (1) [23]:
tavg
Jt • I (t )dt
(1)
jl(t)dt '
where I(t) is the dependence of the luminescence intensity over time, t is time.
The estimated mean luminescence lifetime values show that concentration quenching is mostly manifested for Yb3+ ions (Table 2). In this case, the decrease in the luminescence lifetime in the IR region with an increase in the number of Eu3+ ions is insignificant, which indicates an insignificant effect of energy transfer back to the Eu3+ ions for the YF3 matrix. This mechanism was described in [24].
Using the integrating sphere, we determined the quantum yield of luminescence of Yb3+ ions (OY) upon excitation of the samples in the region of 266 nm (Table 3). The maximum values were recorded for the Eu and Yb ratios of 0.1:10.0 and 0.05:5.00 for the YF3 (OY = 2.2 %).
4. Conclusions
Using the method of high-temperature melting, single-phase samples of solid solutions of Y, Eu Yb F_ with different amounts of Eu3+
1—x—y x y 3
and Yb3+ cations were synthesized. The powder samples of these crystals were described using of X-ray diffraction, energy dispersion analysis, and
optical luminescent spectroscopy. Compliance with the b-YF3 structural type was confirmed for all samples. A monotonic change in the unit cell parameters indicates the formation of solid solutions of the same phase, while the deviation of the real composition from the nominal did not exceed ± 0.5 mol%. The study of luminescence of the samples doped with both Eu3+ and Yb3+ ions showed the luminescence spectra of Eu3+ and Yb3+ ions, which are characteristic of these compounds. Both ions became luminescent upon excitation at wavelengths of 266 and 296 nm. It was also shown that, upon excitation at a wavelength of 266 nm, a wide luminescence band with a centre of approximately 430 nm appears. It may be due to the 5d-4f transition of Eu2+ ions. This leads to the fact that the kinetics of the luminescence decay of Eu3+ ions significantly differs from the exponential. In the luminescence kinetics, a short component can be distinguished, with the lifetime decreasing when the number of Yb3+ ions increases, and a long component, whose lifetime increases. Most likely, there is an energy transfer from Eu3+ ions to Yb3+ ions. Using the integrating sphere, we measured the quantum yield of luminescence of Yb3+ ions upon excitation at a wavelength of 266 nm. The quantum yield values of down-conversion luminescence were recorded for the Eu and Yb ratios of 0.1:10.0 and 0.05:5.00 for the YF3 (OY = 2.2 %).
Conflict of interests
The authors declare that they have no known competing financial interests or personal
Table 2. The mean luminescence lifetime, recorded at wavelengths of 615 nm and 1020 nm in the YF 3: Eu:Yb samples upon excitation at a wavelength of 266 nm
YF
Recording wavelength 615 nm 615 nm 1020 nm 615 nm 1020 nm 615 nm 1020 nm
Composition Yb 0% Yb 1.0 mol% Yb 5.0 mol% Yb 10.0 mol%
Eu 0.05 mol% 2.6±0,1 ms 2.3±0.1 ms 1.7±0.1 ms 3.0±0.1 ms 1.3±0.1 ms 3.7±0,1 ms 1.0±0.1 ms
Eu 0.1 mol% 2.8±0.1 ms 2,1±0.1 ms 1.6±0.1 ms 2,7±0.1 ms 1.3±0.1 ms 3.5±0.1 ms 1.1±0.1 ms
Table 3. The quantum yield of the Yb3+ luminescence in the YF3:Eu:Yb samples upon 266 nm excitation
YF3:Yb:Eu
Composition Yb 1.0 mol% Yb 5.0 mol% Yb 10.0 mol%
Eu 0.05 mol% 1.0 % 2.2 % 1.6 %
Eu 0.10 mol% 1.0 % 1.1 % 2.2 %
relationships that could have influenced the work reported in this paper.
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Information about the authors
Sergey V. Kuznetsov, PhD in Chemistry, Leading Researcher, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russian Federation; e-mail: kouznetzovsv@gmail.com. ORCID iD: https://orcid.org/0000-0002-7669-1106.
Aleksei S. Nizamutdinov, PhD in Physics and Mathematics, Associate Professor, Kazan Federal University; Kazan, Russian Federation; e-mail: anizamutdinov@mail.ru. ORCID iD: https://orcid. org/0000-0003-1559-6671.
Eduard I. Madirov, Postgraduate student, Kazan Federal University, Kazan, Russian Federation; e-mail:
ed.madirov@gmail.com. ORCID iD: https://orcid. org/0000-0001-7092-8523.
Vasilii A. Konyushkin, PhD in Technical Sciences, Head of Laboratory, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russian Federation; ORCID iD: https://orcid.org/0000-0002-6028-8937.
Andrei N. Nakladov, Research Fellow, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russian Federation; ORCID iD https://orcid.org/0000-0002-4060-8091.
Valery V. Voronov, PhD in Physics and Mathematics, Head of Laboratory, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russian Federation; e-mail: voronov@lst.gpi.ru. ORCID iD: https://orcid.org/0000-0001-5029-8560.
Aleksei D.Yapryntsev, Postgraduate student, Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, Moscow, Russian Federation; ORCID iD: https://orcid.org/0000-0001-8166-2476.
Vladimir K. Ivanov, DSc in Chemistry, Associate Member of the Russian Academy of Sciences, Director of the Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, Moscow, Russian Federation; e-mail: van@igic.ras.ru. ORCID iD: https://orcid.org/0000-0003-2343-2140.
Vadim V. Semashko, DSc in Physics and Mathematics, Professor, Kazan Federal University, Kazan, Russian Federation; ORCID iD: https://orcid.org/0000-0003-4967-1991.
Pavel P. Fedorov, DSc in Chemistry, Head of Department, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russian Federation; e-mail: ppfedorov@yandex.ru. ORCID iD: https://orcid.org/0000-0002-2918-3926.
All authors have read and approved the final manuscript.
Translated by Anastasiia Ananeva
Edited and proofread by Simon Cox
