The spectroscopic properties of cerium ions in various aluminosilicate glasses modified by Mg2+, Ca2+, Ba2+ and Na+ were investigated in order to optimize these for the potential utilization as Ce3+/Yb3+ quantum cutting material. An increasing optical basicity of the glasses results in a shift in the peak position of the 5d-4f emission of Ce3+ to longer wavelengths and in a decrease in the Ce3+ fluorescence intensity due to decreasing Ce3+/Ce4+ ratios. Argon-bubbling of the melt and supplying argon as melting atmosphere and/or using small amounts of metallic aluminum powder as raw material led to an almost complete reduction of Ce4+ to Ce3+. This resulted in much higher intensities of the Ce3+ fluorescence emission which runs parallel to a decreasing charge transfer absorption of Ce4+. From the absorption spectra of these samples extinction coefficients for Ce4+ and Ce3+ were calculated. For this purpose, an additional sample was prepared by using oxygen bubbling of the melt. An increasing cerium concentration shifts the Ce3+ emission peak position to longer wavelengths, while up to 2·1020 ions per cm3 only a slight increase in the Ce3+ emission intensity was observed. At higher dopant concentrations, a drastic decrease in the Ce3+ fluorescence emission is observed which is most likely attributed to an increasing Ce4+ concentration. High intensity Ce3+ blue emission matching the spectroscopic requirements for potential quantum cutting in Ce3+/Yb3+ codoped glasses could be achieved with a barium aluminosilicate glass.
© 2015 Optical Society of America
Cerium doped glasses are attractive materials for a broad range of applications. Cerium ions can act as sensitizer in luminescent glasses as e.g. scintillator or laser glasses, they are widely used as sensitizer in photo-thermo-refractive glasses, they are often used to decrease photo-darkening in optical fibers or as decolorizing agent for container glass. Furthermore, most white emitting LEDs are based on Ce3+-doped yttrium-aluminum-garnet (YAG) phosphors which act as wavelength converter.
Recently Ce3+ was proposed as sensitizer ion for quantum cutting materials due to its high absorption cross section and strong fluorescence emission [1, 2]. Quantum Cutting (QC) is the emission of two or more low energy photons upon the absorption of one high energy photon. This effect attained great attention due to its potential utilization in the improvement of photonic materials. Efficient NIR QC in an UV excited photonic material will result in quantum efficiencies higher than unity and therefore increase the quantum yield of these materials. Possible applications are e.g. the improvement of solar cells or wavelength converters for optical sensors. Up to now mostly crystalline quantum cutting materials are described in literature, but lately S. F. Zou et al. have shown that QC is also possible in glasses . To achieve QC, Ce3+-Yb3+ codoping in oxyfluoride glasses has been used in this case. For energy transfer between fluorophores, the transfer efficiency mainly depends on the spectral overlap of the emission spectrum of the sensitizer ion and the absorption spectrum of the acceptor ion [4, 5]. In principle this is also valid for energy transfer in QC materials , but here the self-convoluted absorption spectrum of the acceptor ion has to be used . However, the spectral overlap between sensitizer and acceptor ion was not high in Ref. . A further optimization of the spectral overlap should increase the efficiency of the quantum cutting material. This can be achieved by the variation of the chemical composition of the host glass since the transitions involved in the Ce3+ fluorescence are parity allowed 4f-5d electric dipole transitions which are strongly dependent on the local surrounding of the Ce3+ sites. This is not only the reason of the strong absorption and emission of Ce3+ but also allows the shift of the Ce3+ absorption and emission spectra over a very broad spectral range. An optimal QC energy transfer from Ce3+ to Yb3+ should be obtained if the Ce3+ emission wavelength matches with twice the energy of the Yb3+ absorption in the same host [6, 7], which is about 465 nm in aluminosilicate glasses . Aluminosilicate glasses are very promising host matrices for utilization of this effect since they offer chemical stability over an exceptionally broad compositional range [e.g 9, 10]. Furthermore they offer a high chemical durability, high mechanical strength, high rare earth solubility, relatively small coefficients of thermal expansion and low production costs [e.g 8–12].
Besides the spectroscopic properties of the Ce3+ doped host material also the red-ox state of the cerium ions is crucial for its utilization as QC sensitizer. As a polyvalent ion cerium might occur in glasses as Ce3+ and Ce4+. The ratio of the concentrations of these two oxidation states mainly depends on the composition of the glass [13, 14], the oxygen activity of the melt which might also be affected by the furnace atmosphere [14–16] and the temperature of melting [14, 16, 18]. As in the case of all other polyvalent ions, also Ce3+ and Ce4+ form an equilibrium with the physically dissolved oxygen of the melt according to 4 Ce3+ + O2 ↔ 4 Ce4+ + 2 O2-. The equilibrium is shifted to Ce3+ with increasing temperature, decreasing basicity and the application of reducing melting conditions. In principle, the equilibrium constants of redox reactions can be determined by equilibration experiments  or, however, using electrochemical measurements. Smythe et al. presented a calibration method for the quantitative determination of Ce3+/Ce4+-ratios in alkali-aluminosilicate glasses using Ce M4,5-edge X-ray absorption near edge structure (XANES) spectroscopy . It was further tried to separate the Ce3+ and Ce4+ absorption bands by spectroscopic methods [17, 20–24]. This is difficult since Ce3+ and Ce4+ ions both show broad-band and largely overlapping near UV absorption. Furthermore, up to now a clear evidence of any Ce4+ fluorescence emission has not been found, which could help to separate the absorption bands via fluorescence excitation measurements. However, only one of these workgroups applied reducing and oxidizing melting conditions to enable a clear separation of the Ce3+ and Ce4+ absorption bands . Since this work was done in phosphate and fluoride phosphate glasses of relatively low optical basicity, and low melting temperature only small amounts of Ce4+ could be obtained.
For effective Ce3+-Yb3+ quantum cutting, glasses of relatively high optical basicity have to be used. In these materials, the co-existence of Ce4+ which has an extremely strong and broad charge transfer transition would dramatically decrease the absorption of UV photons by Ce3+ ions. This would result in very low Ce3+ emission intensities and in low quantum yields even at high energy transfer rates to the acceptor ion. Therefore a detailed knowledge of the influence of the host matrix, the melting conditions and the overall cerium concentration on the spectral properties of Ce3+ and the Ce3+/Ce4+ ratio is needed. This paper presents a systematical study on the spectral properties of Ce3+ and Ce4+ in aluminosilicate glasses, which is of particular importance for the development of QC materials as well as for the research on photo-thermo-refractive glasses.
All glasses were prepared from high purity raw materials (Fe < 10 ppm, other contaminating metals < 0.5 ppm) SiO2 (Sipur A1, Schott, Germany), Al2O3 (Ceralox, Condea Chemie, Germany), MgO (Merck, Germany), CaCO3 (Merck, Germany), Na2CO3 (Merck, Germany), and BaCO3 (VK Labor- und Feinchemikalien, Germany). The batches were melted in covered platinum crucibles (non-reducing melts) or corundum crucibles (reducing melts) at temperatures in the range from 1550 to 1650°C depending on the individual glass composition. After melting for 2 h, the samples were cast into brass moulds and transferred into a muffle furnace, preheated to temperatures in the range from 720 to 920°C. Subsequently, the cooling furnace was switched off and the samples were allowed to cool (cooling rate: approximately 3 K/min).
Starting with a magnesium aluminosilicate glass, different glass compositions of increasing optical basicities have been melted. Table 1 summarizes the chemical compositions, densities and calculated optical basicities of all prepared glasses. Two series of glass samples were prepared; in the first series the cerium concentration was kept constant at 1∙1019 ions per cm3 (about 0.04 mol% CeO2) while varying the glass composition; for the second glass series the glass composition was kept constant (BaAS3510) while the cerium concentration was varied between 5∙1018 and 5∙1020 ions per cm3. The samples were denoted according to their molar chemical composition. Glass samples were doped with cerium ions using CeO2 as an additive to the raw materials.
The density of each glass sample was measured using an AccPyc 1330 pycnometer (Micromeritics, Germany). Fluorescence emission and excitation spectra were measured using a fluorescence spectrometer RF-5301PC (SHIMADZU, Japan). For these investigations, the samples were cut and polished (thickness 10 mm). Cerium excitation spectra were recorded at the wavelength of the emission peak maximum while emission spectra were obtained using the wavelength of the excitation peak maximum (spectral resolution: 0.2 nm). Optical absorption spectra were recorded using a commercial double beam spectrometer UV-3102PC (SHIMADZU, Japan) in the wavelength range of 190–3,200 nm with an error of about 1%. For these measurements, polished samples with a thickness of 0.1 to 1 mm were used.
Results and discussion
The effect of glass composition
Figure 1 shows the fluorescence emission and excitation spectra recorded from various glass compositions all doped with a cerium concentration of 1∙1019 ions per cm3 which corresponds to about 0.04 mol% CeO2 depending on the density of the glass. All curves show a pronounced maximum. The peak emission and excitation of the magnesium containing glass MgAS2020 occur at the smallest wavelengths (385 and 340 nm, respectively) while those of the barium containing glass BaAS3510 are observed at the largest wavelengths (445 and 365 nm, respectively). The intensity of the emission spectrum is largest in the magnesium containing sample MgAS2020, and decreases within the series CaAS3020, CaBaAS251013, CaNaAS251015. Within this series, a continuous decrease of the peak intensity with increasing wavelength of the peak maximum is observed. The ternary barium aluminosilicate glass is observed at the largest wavelength, however, it shows a clearly more intense fluorescence emission than the glasses CaBaAS251013 and CaNaAS251015. Obviously, glasses of larger optical basicity show emission at lower wavenumbers / larger wavelengths (see Table 1). The optical basicity is a phenomenological measure of the electron donor power of an oxidic compound. It is closely related to the polarizability of the material and can be calculated from experimentally determined or theoretically derived basicity values of the individual oxides . For the calculation of the theoretical basicities of the glass compositions the averaged partial basicity values of Duffy and Lebouteiller/Courtine given in Ref. . have been used. The observed dependency on the chemical composition of the glasses can be explained as follows: An increasing optical basicity of the glass composition is related to an increasing polarizability at the local rare earth sites. According to Dorenbos [25, 26] an increasing polarizability results in an increasing shift of the 5d1 energy level of Ce3+ to lower energies which is equivalent to a red-shift of the absorption and emission spectra. In particular the polarizability is reported to increase in the order Mg2+ < Ca2+ < Na+ < Ba2+  which exactly resembles the order of the optical basicities of the respective oxides [27, 28]. The splitting of the 5d1 energy level has a further influence on the spectral position of the absorption/emission peaks. Stronger splitting results in an additional red shift of the spectra. The splitting is reported to be mainly dependent on the Ce3+ coordination number and Ce-O bond length but independent of the shift of the 5d1 level . Hence, varying the glass composition in order to increase the optical basicity results in the desired shift to longer wavelengths of the Ce3+ emission as seen in Fig. 1. Furthermore, it can be seen that the Ce3+ emission spectra consist of two components (non-symmetrical shape of the emission spectra). This effect is due to the two 4f1 energy levels (2F5/2 and 2F7/2) which are the final states of the fluorescence transition 5d1→ 4f1. 2F5/2 is the ground state while the 2F7/2 level is located at around 2,000 cm−1  which corresponds very well to the spectra.
Figure 1 additionally includes an energy-doubled absorption spectrum of Yb3+ doped MgAS2020 glass (grey short-dashed line, doping concentration 1∙1020 ions per cm3). The peak is due to the ground state (2F7/2) absorption of the 3-fold splitted 2F5/2 level of the Yb3+ ion. Since this transition is an f-f transition it is – in contrast to the f-d transitions of Ce3+ – hardly affected by the glass composition . Its distinctive tall peak is located at about 980 nm in aluminosilicate glasses, the broader subpeak is observed at a smaller wavelength of about 930 nm  (in Fig. 1 displayed at 490 and 465 nm, respectively). The largest overlap between the Ce3+ emission and the energy-doubled Yb3+ absorption in principle may be obtained by the high basicity BaAS3510 glass which shows the Ce3+ emission peak at around 445 nm. However, by melting under air only a relatively small fluorescence emission intensity is obtained with this glass composition.
The notable decrease in Ce3+ fluorescence intensity of glasses with higher optical basicity is in agreement with the literature where a shift of red-ox equilibria to the higher oxidation state with increasing basicity has often been described [13, 14] (see also introduction section). Therefore under constant melting conditions, the Ce4+ concentration should be higher in glasses of higher optical basicity. Due to the large spectral overlap of the absorption spectra of Ce3+ and Ce4+ and the strong charge transfer absorption of Ce4+ more radiation is absorbed by Ce4+ which does not result in fluorescence emission in these glasses.
The effect of reducing melting conditions
In order to further evaluate the effect of Ce4+ and to increase the emission intensity of Ce3+ in high basicity glasses, three different reduction techniques were applied in this work: melting with argon bubbling for 1 h (curve b in Fig. 2), melting with argon bubbling for 1 h under argon atmosphere (curve c in Fig. 2) and replacing a small part of the aluminum oxide by metallic aluminum powder in the batch (curve d in Fig. 2). For the latter, 0.5 mol% of Al2O3 were replaced by 1 mol% Al-powder. The glass composition of the highest optical basicity BaAS3510 and a cerium doping concentration of 1∙1019 cm−3 were used for these experiments. In Fig. 2 the fluorescence excitation and emission spectra of the reduced samples (curves b, c, d) are compared to the unreduced sample (curve a). As expected, reduction of the melt results in an increased Ce3+ fluorescence intensity. Obviously, argon bubbling under air only slightly decreased the Ce4+ concentration. Curves c and d (bubbling with argon under argon atmosphere and reducing by Al-powder respectively) show maxima which are in an almost perfect agreement. This indicates an almost complete reduction of Ce4+ to Ce3+ in both cases. Overall, the Ce3+ fluorescence intensity increased by a factor of about 2.4 in these two samples in comparison to the unreduced sample.
Figure 3 shows the absorption spectra of BaAS3510 glass samples doped with 1∙1019 cerium ions per cm3, melted under reducing (long-dashed line), not reducing (full line) and oxidizing conditions (short-dashed line). For oxidation, the melt was bubbled with oxygen for 2 hours and subsequently casted without refining. An oxidized sample (oxygen bubbling) and a reduced sample (argon bubbling) of this series are shown in Fig. 4(sample thickness 1 cm, sample size about 3 × 2 cm). Although the doping concentration is very low, the oxidized sample shows a clear yellow/brownish coloring while the reduced sample is clear and colorless.
To separate the optical absorption due to Ce3+ and Ce4+ ions from the absorption of impurities, the spectra of reduced, oxidized and unreduced blank glass samples have been measured and subtracted from the respective spectra of doped samples in Fig. 3. At a wavenumber of about 31,000 cm−1, the most intense Ce3+ absorption peak (4f1 → 5d1) is observed which is clearly visible for the reduced and not reduced samples. For the oxidized sample, this peak is much smaller. However, since the 5d1 energy level of Ce3+ is split into 5 sublevels [21, 29–31], four more Ce3+ absorption bands should be visible. On the other hand, it is well known that the charge transfer transition of Ce4+ is also located in this spectral range (see spectra of not reduced and oxidized samples). Therefore, it is difficult to decide whether the spectrum of the reduced sample solely represents the absorption of Ce3+ or a superposition of transitions of both Ce3+ and Ce4+ ions in the range from 47,000 to 31,000 cm−1. In Fig. 2 Ce3+ fluorescence spectra of two strongly reduced samples are shown which are in very good agreement, although they had been produced by completely different methods. This is a hint that the maximum possible amount of Ce3+ has already been achieved in theses samples. To further evaluate this assumption, samples of different cerium concentrations have been prepared with the aluminum powder reduction method. Up to a concentration of 2∙1020 cm−3 all these spectra have almost the same shape (not shown). Samples of higher cerium concentration could unfortunately not be measured, due to the too strong absorption of Ce3+, even at a sample thickness of only 0.1 mm. From these measurements it can be concluded that the reduction potential of 1 mol% aluminum powder is sufficient to reduce the entire cerium concentration to Ce3+. In fact 1 mol% CeO2 corresponds to a concentration of about 2.5∙1020 cerium ions per cm3 in this glass. It should further be mentioned that one mol% metallic aluminum should be sufficient to reduce 3 mol% CeO2 (2 Al + 6 CeO2 → Al2O3 + 3 Ce2O3), however, a part of the metal might also be oxidized e.g. by CO2 from the used raw materials.
Ebendorff-Heidepriem and Ehrt  also reported a complete reduction of cerium to Ce3+ (1.5 and 2∙1019 cm−3) in phosphate and fluoride phosphate glasses by melting with the addition of sugar to the batch or by remelting the glasses in carbon crucibles under argon atmosphere. In both cases, melting temperatures of 1100 °C have been used. Johnston  reports that the percentage of Ce4+ in a sodium silicate glass could be reduced from 68 to 22% only by applying CO2 atmosphere instead of melting in air at 1085 °C. A further hint that all of the cerium could be reduced by using the presented methods at low cerium concentrations can be found in Ref. : Schreiber et al. measured the red-ox equilibria of different ions as e.g. Eu2+/3+, Fe2+/3+ and Ce3+/4+ in aluminosilicate glasses at 1500 °C. It is stated that cerium has the highest reduction potential of these ions and therefore is much easier to reduce than e.g. europium. In an earlier work on the fluorescence properties of europium, we reported an almost complete reduction of Eu3+ to Eu2+ in borosilicate glasses by using similar, strongly reducing melting conditions . Although the glass composition had a lower optical basicity in that case it might be a further indirect hint that all of the cerium could be reduced to Ce3+ in the present experiments. However, in order to further evaluate the measured absorption spectra, they were deconvoluted using curves of Gaussian shape.
Figures 5, 6 and 7 represent three examples of deconvolution of absorption spectra of a reduced, a not reduced and an oxidized cerium doped sample respectively (BaAS3510, 1∙1019 Ce3+/4+ cm−3, also displayed in Fig. 3). Since it can be assumed that most of the cerium is reduced to Ce3+ in the reduced sample (Fig. 5) it has been tried to fit 5 Gaussian peaks to the spectrum since the 5d1 level is split up into 5 components as explained earlier. The positions of the peaks are about 30,000, 30,700, 32,000, 37,200 and 45,700 cm−1. Especially the relative spectral position of the three peaks of lower energies corresponds well to literature data, e.g. 33,000, 34,500 and 36,400 cm−1 in YAlO3 . The peak positions of the two peaks observed at higher energies of about 37,200 and 45,700 cm−1 still fit relatively well (41,900 and 45,500 cm−1 ). Similar Ce3+ f-d band positions are also reported for borax glasses . In phosphate and fluoride phosphate glasses, the band positions are reported to be more equally distributed between 34,000 and 49,000 cm−1 . However, Ce3+ band positions and line widths can be much different for different host materials [21, 25, 26, 29, 30, 33]. Furthermore, especially for the high energy band, the reliability of the measurements and fits is relatively low since in this spectral range also the absorption of the glass matrix is observed. In addition, here the charge transfer absorption of Ce4+ is located, which consists of 2 bands [21, 23]. Therefore, also a superposition of Ce4+ and Ce3+ absorption bands could be observed here, which cannot be separated clearly.
Figure 6 shows the deconvolution of the absorption spectrum of the unreduced sample. As can be seen the absorption at wavenumbers above 35,000 cm−1 strongly increased in intensity. To separate the absorption bands of Ce4+ and Ce3+ in this spectrum, the bands of Ce3+ obtained from the deconvolution in Fig. 5 have been added at the same spectral positions. Then two more peaks at higher energies have been added which resemble the 2 band absorption of Ce4+. While keeping the positions, relative intensities and shape of the five assumed Ce3+ peaks constant, it has been tried to fit the two additional Ce4+ peaks to the spectrum. This approach worked reasonably well. Under the assumption that the reduced sample (Fig. 5) contains solely Ce3+, a molar extinction coefficient of 807 l∙mol−1∙cm−1 for Ce3+ at a wavelength of 324 nm was calculated. Using this result, the deconvolution shown in Fig. 6 furthermore enables to calculate the extinction coefficient of Ce4+. According to the fit, the intensity of the Ce3+ peak decreased to 67% in comparison to the reduced sample. In turn this means that the Ce4+ concentration in the not reduced sample is 0.33∙1019 cm−3 and a molar extinction coefficient of 4,627 l∙mol−1∙cm−1 can be calculated for Ce4+ at 250 nm in this sample. In the same way the extinction coefficient of Ce4+ can also be calculated from the absorption spectrum of the oxidized sample (Fig. 7). Here, a Ce4+ concentration of 0.53∙1019 cm−3 and an extinction coefficient of 4,843 l∙mol−1∙cm−1 at 250 nm was calculated. These results are summarized in Table 2.The relative difference of less than 5% for these two calculations proves, that the assumptions that the reduced sample (Fig. 5) only contains Ce3+ and the Ce3+ extinction coefficient is about 807 l∙mol−1∙cm−1 are justified. The average value of these two molar extinction coefficient values is 4,735 l∙mol−1∙cm−1. However, it must be pointed out that the relative intensities of the two Ce4+ peaks are obviously not the same in the two deconvolutions shown in Figs. 6 and 7. In analogy, a slight difference in the peak positions of these two peaks in both deconvolutions is observed. From the absorption spectra reported by Ebendorff-Heidepriem and Ehrt , a molar extinction coefficient of about 710 l∙mol−1∙cm−1 at 290 nm can be deduced for Ce3+ in a phosphate glass, and a value of about 470 l∙mol−1∙cm−1 at 265 nm for a fluoride phosphate glass. Especially the value for the phosphate glass is fairly close to our result. However, the reported extinction coefficients for Ce4+ are much lower than in the glasses presented here (2,230 and 720 l∙mol−1∙cm−1 for phosphate and fluoride phosphate glass respectively). This might be a hint that not all cerium occurred as Ce3+ in those samples; most likely due to the much lower melting temperature of these glass compositions.
From Fig. 7, it is also obvious that the low energy absorption peak of Ce4+ extends far into the visible range resulting in the yellow/brownish coloring of this glass (left sample in Fig. 4). As a result, the following conclusions can be drawn: The extinction coefficient of Ce4+ can roughly be estimated to be about 6 times larger than the extinction coefficient of Ce3+ at their respective peak wavelengths. Due to the extremely broad Ce4+ absorption peak at around 37,000 cm−1, the absorption spectrum of Ce4+ extends far into the visible range of the spectrum. Therefore the yellow/brownish coloring of the samples is due to the Ce4+ absorption although the peak positions of the Ce4+ bands are located at much higher energies than the Ce3+ absorption.
The effect of cerium concentration
Excitation and emission spectra of samples with different cerium concentrations are shown in Fig. 8.All of these samples are of the glass composition BaAS3510 and have been melted using 1 mol% metallic aluminum powder as reducing agent replacing 0.5 mol% of Al2O3 in the batch. With increasing cerium concentration, the intensities in the spectra increase while the peak position is slightly shifted towards lower wavenumbers / higher wavelengths. The spectral shift indicates an increase of the optical basicity with increasing cerium concentration.
The intensity increase up to a concentration of 2∙1020 ions per cm3 can be attributed to the increasing Ce3+ concentration and therefore to a higher quantity of radiation centers. Nevertheless, the intensity increase is much lower than the respective Ce3+ concentration increase. Furthermore the above mentioned shift of the spectra due to the increasing optical basicity is much too large to be solely attributed to the relatively small increase in cerium concentration. Possibly these effects are due to clustering of the cerium ions in these glasses which would result in an increased local basicity (spectral shift) due to the high optical basicity of cerium oxide (0.65 ) and increased concentration quenching (non-proportional intensity increase) at the cerium sites. However, further work is needed to fully understand this effect. A further increase in the cerium concentration to 5∙1020 ions per cm3 (about 2 mol% CeO2) results in a drastic decrease of the emission intensity. At this point, the concentration of cerium exceeds the concentration of metallic aluminum in the batch necessary to reduce all Ce4+ and hence a fairly high concentration of Ce4+ is still present. This is supported by the color of the glass samples. While the samples with low cerium concentrations are colorless, samples of higher cerium concentration tend to be yellow/brownish. The sample with 5∙1020 cerium ions per cm3 even appears light brown. The coloring is due to the broad charge transfer absorption band of Ce4+ which extends far into the visible part of the spectrum as shown earlier. Concentration quenching might play an additional role in the intensity decrease at cerium concentrations above 2∙1020 ions per cm3.
The effect of the glass composition, optical basicity and melting conditions on the Ce3+/Ce4+ ratio and the spectral properties and intensity of the Ce3+ fluorescence was studied in aluminosilicate glasses. In samples of high optical basicity, the Ce3+ excitation and emission peak positions shift towards longer wavelengths while the Ce3+/Ce4+ ratio decreases. Increasing amounts of Ce4+ can efficiently hinder the excitation of Ce3+ due to their broad and very intensive charge transfer absorption. The application of strongly reducing melting conditions can counteract this effect. High intensity blue emission matching the spectroscopic requirements for potential quantum cutting in Ce3+/Yb3+ codoped glasses could be achieved with a barium aluminosilicate glass. The molar extinction coefficients of Ce3+ and Ce4+ at their respective absorption peaks were calculated to be around 807 and 4,735 l∙mol−1∙cm−1, respectively.
This work was supported by the European Social Fund (ESF) through the Thuringian Ministry of Economy, Employment and Technology (project number 2011 FGR 0122).
References and links
1. J. Chen, H. Guo, Z. Li, H. Zhang, and Y. Zhuang, “Near-infrared quantum cutting in Ce3+, Yb3+ co-doped YBO3 phosphors by cooperative energy transfer,” Opt. Mater. 32(9), 998–1001 (2010). [CrossRef]
2. H. Zhang, J. Chen, and H. Guo, “Efficient near-infrared quantum cutting by Ce3+-Yb3+ couple in GdBO3 phosphors,” J. Rare Earths 29(9), 822–825 (2011). [CrossRef]
3. S. F. Zou, Z. L. Zhang, F. Zhang, and Y. L. Mao, “High efficient quantum cutting in Ce3+/Yb3+ co-doped oxyfluoride glasses,” J. Alloy. Comp. 572, 110–112 (2013). [CrossRef]
4. T. Förster, “Experimentelle und theoretische Untersuchung des zwischenmolekularen Übergangs von Elektronenanregungsenergie,” Z. Naturforschung 4a, 321–327 (1949).
5. D. L. Dexter, “A theory of sensitized luminescence in solids,” J. Chem. Phys. 21(5), 836–850 (1953). [CrossRef]
6. P. Vergeer, T. J. H. Vlugt, M. H. F. Kox, M. I. den Hertog, J. P. J. M. van der Eerden, and A. Meijerink, “Quantum cutting by cooperative energy transfer in YbxY1-xPO4:Tb3+,” Phys. Rev. B 71(1), 0141901 (2005). [CrossRef]
7. D. L. Dexter, “Cooperative optical absorption in solids,” Phys. Rev. 126(6), 1962–1967 (1962). [CrossRef]
8. M. Tiegel, A. Herrmann, S. Kuhn, C. Rüssel, J. Körner, D. Klöpfel, R. Seifert, J. Hein, and M. C. Kaluza, “Fluorescence and thermal stress properties of Yb3+-doped alumino silicate glasses for ultra high peak power laser applications,” Laser Phys. Lett. 11(11), 115811 (2014). [CrossRef]
9. H. Scholze, Glass - Nature, Structure, and Properties (New York, 1991).
10. A. Herrmann, S. Kuhn, M. Tiegel, C. Rüssel, J. Körner, D. Klöpfel, J. Hein, and M. C. Kaluza, “Structure and Fluorescence Properties of Ternary Alumino Silicate Glasses doped with Samarium and Europium,” J. Mater. Chem. C 2(21), 4328–4337 (2014). [CrossRef]
11. J. E. Ritter Jr and C. L. Sherburne, “Dynamic and Static Fatigue of Silicate Glasses,” J. Am. Ceram. Soc. 54(12), 601–605 (1971). [CrossRef]
12. M. Tiegel, A. Herrmann, C. Rüssel, J. Körner, D. Klöpfel, J. Hein, and M. C. Kaluza, “Magnesium aluminosilicate glasses as potential laser host material for ultrahigh power laser systems,” J. Mater. Chem. C 1(33), 5031–5039 (2013). [CrossRef]
13. A. Paul and R. W. Douglas, “Cerous Ceric Equilibrium in Binary Alkali Borate and Alkali Silicate Glasses,” Phys. Chem. Glasses 6, 212–215 (1965).
14. H. D. Schreiber, H. V. Lauer Jr, and T. Thanyasiri, “The redox state of cerium in basaltic magmas: an experimental study of iron-cerium interactions in silicate melts,” Geochim. Cosmochim. Acta 44(10), 1599–1612 (1980). [CrossRef]
15. V. Gottardi, G. Paoletti, and M. Tornati, “The ratio Ce3+/Ce4+ in the melting of different glasses and its influence on their properties,“ Advances in Glass Technology, VI International Congress in Glass, Washington D.C. 412–423 (1962).
16. W. D. Johnston, “Oxidation-Reduction Equilibria in Molten Na2O 2SiO2 Glass,” J. Am. Ceram. Soc. 48(4), 184–190 (1965). [CrossRef]
17. A. Paul, M. Mulholland, and M. S. Zaman, “Ultraviolet absorption of cerium(Ill) and cerium(IV) in some simple glasses,” J. Mater. Sci. 11(11), 2082–2086 (1976). [CrossRef]
18. J. Mendham, R. C. Denney, J. D. Barnes, and M. J. K. Thomas, Vogel's Quantitative Chemical Analysis (6th ed.), (Pearson Education Limited: Harlow, 2000).
19. D. J. Smythe, J. M. Brenan, N. R. Bennett, T. Regier, and G. S. Henderson, “Quantitative determination of cerium oxidation states in alkali-aluminosilicate glasses using M4,5-edge XANES,” J. Non-Cryst. Solids 378, 258–264 (2013). [CrossRef]
20. A. M. Efimov, N. V. Nikonorov, A. I. Ignatiev, and E. S. Postnikov, “Quantitative UV–VIS spectroscopic studies of photo-thermo-refractive glasses. II. Manifestations of Ce3+ and Ce(IV) valence states in the UV absorption spectrum of cerium-doped photo-thermo-refractive matrix glasses,” J. Non-Cryst. Solids 361, 26–37 (2013). [CrossRef]
21. H. Ebendorff-Heidepriem and D. Ehrt, “Formation and UV absorption of cerium, europium and terbium ions in different valencies in glasses,” Opt. Mater. 15(1), 7–25 (2000). [CrossRef]
22. S. E. Paje, M. A. García, M. A. Villegas, and J. Llopis, “Cerium doped soda-lime-silicate glasses: effects of silver ion-exchange on optical properties,” Opt. Mater. 17(4), 459–469 (2001). [CrossRef]
23. A. M. Efimov, A. I. Ignatev, N. V. Nikonorov, and E. S. Postnikov, “Spectral components that form UV absorption spectrum of Ce3+ and Ce(IV) valence states in matrix of photothermorefractive glasses,” Opt. Spectrosc. 111(3), 426–433 (2011). [CrossRef]
24. M.-L. Brandily-Anne, J. Lumeau, L. Glebova, and L. B. Glebov, “Specific absorption spectra of cerium in multicomponent silicate glasses,” J. Non-Cryst. Solids 356(44-49), 2337–2343 (2010). [CrossRef]
25. P. Dorenbos, “5d-level energies of Ce3+ and the crystalline environment. III. Oxides containing ionic complexes,” Phys. Rev. B 64(12), 125117 (2001). [CrossRef]
26. P. Dorenbos, “Relating the energy of the [Xe]5d1 configuration of Ce3+ in inorganic compounds with anion polarizability and cation electronegativity,” Phys. Rev. B 65(23), 2351101–2351106 (2002). [CrossRef]
27. J. A. Duffy, “A review of optical basicity and its applications to oxidic systems,” Geochim. Cosmochim. Acta 57(16), 3961–3970 (1993). [CrossRef]
28. V. Dimitrov and T. Komatsu, “An interpretation of optical properties of oxides and oxide glasses in terms of the electronic ion polarizability and average single bond strength,” J. Univ. Chem. Tech. Met. 45, 219–250 (2010).
29. N. J. Weber, “Optical spectra of Ce3+ and Ce3+-sensitized fluorescence in YAlO3,” J. Appl. Phys. 44(7), 3205–3208 (1973). [CrossRef]
30. R. Reisfeld, “Spectra and energy transfer of rare earths in inorganic glasses,” Structure and Bonding 13, 53–98 (1973). [CrossRef]
31. G. Blasse and B. C. Grabmaier, Luminescent Materials (Springer, 1994).
32. A. Herrmann, S. Fibikar, and D. Ehrt, “Time-resolved fluorescence measurements on Eu3+- and Eu2+-doped glasses,” J. Non-Cryst. Solids 355(43-44), 2093–2101 (2009). [CrossRef]
33. G. A. Slack, S. L. Dole, V. Tsoukala, and G. S. Nolas, “Optical absorption spectrum of trivalent cerium in Y2O3, Ba2GdTaO6, ThO2, and related compounds,” J. Opt. Soc. Am. B 11(6), 961–974 (1994). [CrossRef]