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Article

Preparation of Glass-Ceramic Materials by Controlled Crystallization of Eu2O3-Doped WO3-B2O3-La2O3 Glasses and Their Luminescent Properties

by
Aneliya Yordanova
1,
Margarita Milanova
1,*,
Lyubomir Aleksandrov
1,
Reni Iordanova
1,
Peter Tzvetkov
1,
Pavel Markov
1 and
Petia Petrova
2
1
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, G. Bonchev, Str., bld. 11, 1113 Sofia, Bulgaria
2
Institute of Optical Materials and Technologies “Acad. Jordan Malinowski”, Bulgarian Academy of Sciences, blvd. Akad. G. Bonchev 109, 1113 Sofia, Bulgaria
*
Author to whom correspondence should be addressed.
Molecules 2025, 30(4), 832; https://doi.org/10.3390/molecules30040832
Submission received: 30 December 2024 / Revised: 2 February 2025 / Accepted: 8 February 2025 / Published: 11 February 2025
(This article belongs to the Section Materials Chemistry)
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Abstract

:
In this paper, the crystallization behavior of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass has been investigated in detail by XRD and TEM analysis. The luminescent properties of the resulting glass-ceramics were also investigated. By XRD and TEM analysis, crystallization of β-La2W2O9 and La2WO6 crystalline phases has been proved. Photoluminescent spectra showed increased emission in the resulting glass-ceramic samples compared to the parent glass sample due to higher asymmetry of Eu3+ ions in the obtained crystalline phases, where the active Eu3+ ions are incorporated. Also, in the glass-ceramics, the crystalline particles are embedded in the amorphous matrix and more of them are separated from each other which improves the light scattering intensity from the free interfaces of the nanocrystallites, resulting in the enhancement of the PL intensity. It was established that the optimum emission intensity is registered for glass-ceramic samples obtained after an 18 h heat treatment of the parent glass. After 21 h of glass crystallization, the amount of crystallite particles is high enough, and they are in close proximity to each other, and hence, the average distance between europium ions decreases, resulting in quenching of Eu3+ and a decrease in the emission intensity. Additionally, at 21 h of glass crystallization, formation of new crystalline phase—La2WO6 is established. A redistribution of Eu3+ ions in the different crystalline compounds is most likely taking place, which is also not favorable for the emission intensity.

1. Introduction

In recent years, rare earth-based tungstates have gathered increased attention as host materials due to their distinct crystal structure, remarkable emission properties, strong near-ultraviolet (NUV) absorption, thermal and chemical stability, low hygroscopicity, environmental friendliness, and self-activating luminescence properties. In addition, tungstates exhibit a broad charge transfer band (CTB) in the range of 200–350 nm. The CTB can transfer energy to rare earths, making them ideal for UV excitations [1]. In fact, rare earth tungstates are a big family including various compounds of RE2W3O12, RE2WO6, RE6WO12, RE2W2O9, RE10W22O81, and so forth, according to W/RE stoichiometry, and can be viewed as pseudo-binary compositions between RE2O3 and WO3 [2,3]. Among the rare earth tungstates, the compounds of La and tungsten are of great potential for luminescent host materials. For example, La2W2O9:Eu3+ shows promising photoluminescence and has a quantum yield as high as 77% [3,4,5,6]. La2(WO4)3:Tb3+ phosphors were successfully synthesized via an optimized microwave-assisted co-precipitation technique [7]. The luminescence characteristics and structural analyses of Sm3+-activated La10W22O81 microphosphors were also reported [1]. Eu3+:La10W22O81 (LWO) microphosphor rods with intense red emission were synthesized using a hydrothermal-assisted solid-state method [8]. To the best of our knowledge, there are no data for the preparation of lanthanum tungstate glass-ceramics by controlled glass crystallization. In recent years, a great deal of attention has been paid to rare earth-doped glass-ceramic materials, which play a crucial role in many optical applications such as up-conversion fibers, solid-state lasers, medical sensors, optical electronic chips, luminescence labels, optical amplifiers, 3D displays, etc. [9,10]. Glass-ceramics possess excellent characteristics found in both glasses and crystals and have none of the disadvantages of these two materials. Similar to glasses, glass-ceramics have a large capacity for accommodating an active rare earth dopant, are isotropic, and have evenly distributed activators within their bodies. Similar to single crystals, glass-ceramics contain rare earth ions within strictly ordered ligand surroundings. As a result, the presence of a crystalline environment around a rare earth ion allows for high absorption and emission cross-section reduction in the non-radiative relaxation process because of the lower phonon cut-off energy and tailoring of the ion–ion interaction by control of the rare earth ion partition [9,11]. The glass-ceramic materials are usually obtained by subsequent thermal treatment of a glass, which is first melted and annealed as usual. This conventional method relies on thermally induced phase separation and in situ crystallization processes, which are, however, very complex to experimentally control [11]. The choice of an appropriate glass composition is very important for luminescent glass-ceramics elaboration. The search for more efficient glass compositions and guiding structures for rare earth-doped glass-ceramics continues. In our earlier paper, we determined the glass formation region in the ternary La2O3-B2O3-WO3 system. It was established that transparent colorless glasses are obtained in the central part of the system between 20 and 35 mol% La2O3 [12]. We have also studied their structure and crystallization behavior. The main crystallization mechanism in the glasses is the surface crystallization, and the glass in mol % of 50WO3:25La2O3:25B2O3 is crystallized as a single phase LaBWO6 [13]. The luminescence properties of an Eu3+ doped glass, glass-crystalline product, and polycrystalline sample with the same composition of 50WO3:25La2O3:25B2O3 have been verified [12]. It was found that the intensity of emission increases drastically in the glass-crystalline sample consisting of LaBWO6:Eu3+ nanocrystals compared with the glass and polycrystalline samples. These results provoked our interest in continuing the investigation into an La2O3-B2O3-WO3 system. The purpose of the present study is to investigate the crystallization behavior of one selected glass composition from the isothermal section LaBWO6-La2W2O9 of the phase diagram [14] in order to check for the possibility of obtaining lanthanum tungstate glass-ceramics doped with Eu3+ ions and to study their photoluminescence properties. The crystallization behavior of glass-ceramics was characterized by X-ray diffraction and transmission electron microscopy. Emission spectra were measured, and color coordinates of the materials were determined.

2. Results and Discussion

2.1. XRD Data and DTA Analysis

The DTA curves for the bulk and powder samples of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass at a heating rate of 10 K/min are shown in Figure 1. An endothermic dip for the glass transition and exothermic peak for crystallization are clearly observed in both samples. The values of the glass transition and crystallization peak temperatures are Tg = 610 °C and Tc = 700 °C for the bulk sample, and Tg = 600 °C and Tc = 720 °C for the powder glass sample. The difference in the Tc values of bulk and powder 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass implies that a surface crystallization is taking place in this glass. The glass-ceramics (GCs) have been prepared by heat treatment of the precursor glass 52WO3:22B2O3:26La2O3:0.5Eu2O3 at 680 °C, which is the temperature at the beginning of the glass crystallization peak in the DTA curve of the bulk glass sample for 3 h, 6 h, 9 h, 15 h, 18 h, and 21 h.
Figure 2 shows the powder diffraction patterns after crystallization of glass with composition 52WO3:22B2O3:26La2O3:0.5Eu2O3 at a temperature of 680 °C and a crystallization time of 3, 6, 9, 12, 15, 18, and 21 h, respectively. The glass-ceramics obtained after heat treatment of the parent glass for different lengths of time are designated as GC-3 h, GC-6 h, GC-9 h, GC-12 h, GC-15 h, GC-18 h, and GC-21 h, respectively.
From the phase analysis performed, the best match was found to be β-La2W1.7Mo0.3O9 (PDF # 01-073-9174), which is isostructural to the high-temperature polymorphic modification of La2Mo2O9 and crystallizes in cubic space group P213 with parameter a = 7.1327 Å [15]. After 21 h of glass crystallization, the appearance of an additional crystalline phase of orthorhombic La2WO6 was observed. To the best of our knowledge, no La2W2O9 with a cubic structure at room temperature has been reported so far.
Lanthanum molybdate is known to have two polymorphic modifications: an α-La2Mo2O9 low-temperature monoclinic form that is stable below 580 °C and a β-La2Mo2O9 cubic phase that is stable above this temperature [16]. Similarly, lanthanum tungstate also exhibits a reversible polymorphic transition at 1070 °C: a triclinic low-temperature α-La2W2O9 form and a cubic high-temperature β-La2W2O9 polymorph [17]. It is assumed that cubic lanthanum tungstate is isostructural to β-La2Mo2O9. According to our literature review, a crystal structure for β-La2W2O9 has not yet been published. Generally, the stabilization at room temperature of the high-temperature polymorphic modification of La2Mo2O9 and La2W2O9 is carried out with suitable cationic substitutions [18], and only β-La2W1.7Mo0.3O9 is reported as a single stable phase at room temperature without a reversible phase transition [15]. Based on this, we suggest that in our study, the isomorphous substitution of La3+ by Eu3+ has an influence on the stabilization of the cubic symmetry phase of La2W2O9. Moreover, in the chemical composition of the resulting glass, there are no other possibilities for isomorphic substitutions in the structure of β-La2W2O9.
Table 1 presents the calculated unit cell parameters and crystallite size for all stages of the crystallization of cubic β-La2W2O9. No significant change in unit cell parameters as a function of crystallization time is observed from the data. The small variations observed are most likely due to the conditions during powder pattern collection. This study was conducted on a bulk sample of initial glass, which inevitably has some surface irregularities and leads to systematic errors during X-ray diffraction. The calculated crystallite size also remains within narrow limits, between 27.8(6) nm and 22.1(4) nm, regardless of the crystallization time. The reasons for this are most likely kinetic, with the limiting factor in this case being the relatively low crystallization temperature of 680 °C.

2.2. Luminescent Properties

To investigate the effect of heat treatment (level of crystallinity) on luminescent properties, we compared the excitation and emission spectra of 0.5% Eu3+-doped 52WO3:22B2O3:26La2O3 glass with those of the corresponding glass-ceramic (GC) samples obtained at different times of heat treatment at 680 °C. The excitation spectrum (Figure 3) monitored at a 612 nm wavelength (5D0 → 7F2 transition of Eu3+ ions) contains a continuous excitation band below 350 nm and several sharp peaks in the range from 350 nm to 600 nm at 361 nm, 374 nm 381 nm, 392 nm, 413 nm, 462 nm, 523 nm, 530 nm, and 576 nm, which corresponds to characteristic 4f—4f transitions of the Eu3+ ion from 7F0 → 5D4, 7F0 →5G2, 7F0 → 5L7, 7F0 → 5L6, 7F0 → 5D3, 7F0 → 5D2, 7F0 → 5D1, 7F1 → 5D1, and 7F0 → 5D0, respectively [19].
Among the above transitions, the 7F0 → 5L6 one, centered at 392 nm, stands out as the most prominent. Therefore, subsequent emission spectrum measurements were conducted under excitation at 392 nm. The wide band peaking at about 290 nm is assigned to the ligand-to-metal charge transfer states (LMCT) which appeared due to the combined effect of the electronic transition from the 2p orbital of O2− ions to the vacant 4f energy level of the central Eu3+ ions in the Eu—O polyhedral and O2- → W6+ in the WOn groups (WOn = WO4 and WO6) [20,21,22,23,24].
The presence of WOn groups’ excitation band, recorded at the characteristic Eu3+ emission wavelength of 612 nm, suggests that non-radiative energy transfer from the glass matrix to the active rare-earth ion is occurring [24,25]. This mechanism is called host-sensitized luminescence.
As can be seen from Figure 3, the excitation gradually increases with the increase in heat treatment time and reaches a maximum at 18 h and then decreases at 21 h. The same trend is observed in the emission spectra (Figure 4). This enhancement is most likely attributed to the progressive increase in the amount of the crystalline phase in the samples, which alters the crystal field environment inside the matrix, and hence, more efficient excitation of Eu3+ can be expected in the glass-ceramic samples.
Additionally, when comparing the intensity of LMCT and the f-f transitions, it is evident that the intensity is stronger for narrow Eu3+ bands. This is helpful for attaining proper excitation by near-UV and blue LED chips, as the intensity of these Eu3+ transitions is generally weak because they are forbidden by Laporte’s selection rule [26]
The emission spectra in Figure 4 show the conventional emission lines of Eu3+, which corresponds to the transitions from the 5D0 excited energy level towards the 7F0, 7F1, 7F2, 7F3, and 7F4 ground states at about 578, 592, 612, 651, and 700 nm, respectively.
The glass sample possesses the lowest emission intensity, and after obtaining glass-ceramic samples by heat treatment at 680 °C and crystallization of the La2W2O9 phase, the intensity increases up to 18 h of thermal treatment. This enhancement is most likely attributed to the increase in the crystallinity of the sample and due to the incorporation of Eu3+ in the obtained crystal phase.
It is well known that the distorting of the local environment around Eu3+ ions in the host lattice can improve the emission. In particular, the increased photoluminescence emission in glass-ceramics samples compared to the glass is related to the covalency and structural changes in the vicinity of Eu3+ ions (short range effect) [27]. The enhancement of the emission intensity is one proof that site symmetry around the active ion modifies with the glass → crystal transition. On the other hand, in the glass-ceramics, the crystalline particles are embedded in the amorphous matrix and more of them are separated from each other which improves the light scattering intensity from the free interfaces of the nanocrystallites [13], resulting in the increase in the PL intensity.
Additionally, when holding the heat treatment time from 6 h to 9 h, the emission intensity increased by approximately twofold, which is a result of the significant increase in the amount of crystalline phase on the surface (see Figure 2).
After 21 h of glass crystallization, the amount of crystallite particles is high enough and they are in close proximity to each other, and hence, the average distance between europium ions decreases, resulting in quenching of Eu3+ luminescence. As a result of the reduced amount of the amorphous phase on the surface, the effect of light scattering is also reduced, leading to a decrease in emissions. Additionally, at 21 h of glass crystallization, the formation of the new crystalline phase, La2WO6, is established. A redistribution of Eu3+ ions in the different crystalline compounds is most likely taking place, which is also not favorable for the emission intensity. The X-ray structural data and TEM analysis support these observations.
It is established that the ratio of 5D0 → 7F2 to 5D0 → 7F1 transitions may provide structural hints about the distortion of the crystal field environment around the rare earth ions. The 5D0 → 7F1 transition is a magnetic dipole (MD) transition among Eu3+ emission spectra and is permitted by Jude–Offelt theory. Its intensity is not influenced by the environment near Eu3+ ions. In contrast, the 5D0 → 7F2 transition is an electric dipole transition (ED), and its intensity is strongly dependent on the ligand environment. The dominance of the 5D0 → 7F2 transition over the 5D0 → 7F1 transition in the emission spectra (Figure 4) is an indication that the environment surrounding Eu3+ in the samples is non-centrosymmetric. In particular, the site symmetry of Eu3+ can be evaluated by using the integrated emission intensity ratio (R) of these two transitions 5D0 → 7F2/5D0 → 7F1. Higher values of R indicate more site asymmetry of the rare-earth ion, high covalency between Eu3+ and O2- ions, increased emission intensity, and, hence, greater potential for optical applications [16,17,28].
The calculated intensity ratios R (from 4.88 to 6.12) of the Eu3+-doped 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and glass-ceramics (Table 2) are mostly higher than other reported Eu3+ oxide compositions [29,30,31,32,33,34,35,36]. It is also evident from Table 2 that the asymmetry ratio of the glass-ceramics is higher than that of glass and progressively rises with increasing heat treatment time of the samples up to 18 h (GC-18 h), which demonstrates that the degree of symmetry of Eu3+ ions decreases, and a strong Eu-O covalence is formed at a higher level of crystallinity. The larger the asymmetry, the greater the luminous intensity, and this fact is directly related to the higher emission intensity of glass-ceramics. This result is consistent with the intensity trend in PL spectra, where the intensity increases with an increase in the crystallinity level. At 21 h of heat treatment (CG-21), a decrease in the R value is observed, which agrees with the decrease in the emission intensity of this specimen.
Additionally, the appearance of the sensitivity to the crystal field and the forbidden 5D0 → 7F0 transition based on the standard Judd–Ofelt theory [37] indicates that the Eu3+ ion occupies non-centrosymmetric sites with C2ν, Cn, or Cs symmetry [38].
The Commission International de I’Eclairage (CIE) 1931 chromatic diagram is a standardized method for characterizing colors of emission. The chromaticity coordinates of Eu3+-doped 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and glass-ceramics in Table 3 are calculated from the emission spectra by using the color calculator software SpectraChroma Version 1.0.1. (CIE coordinate calculator) [39] and are illustrated in Figure 5. It can be observed that they are located in the red region of the diagram. The estimated coordinates of glass-ceramic samples with average values of 0.650 and 0.345 are represented in the diagram as one point, as the values are almost identical and are very similar to the CIE coordinate of the commercial red phosphor Y2O2S:Eu3+ (0.658; 0.340) [40]. The obtained results show that the investigated glass and glass-ceramics have the potential to be used as red-emitting materials.

2.3. TEM Investigations

A glass-ceramic sample obtained after an 18 h thermal treatment of the parent glass, which exhibited the most intensive luminescent emission, was analyzed using TEM and HRTEM techniques. Morphological studies (Figure 6, Figure 7 and Figure 8) revealed that the sample contains spherical and rectangular nanosized particles. The inset in Figure 7 illustrates the particle size distribution. The nanosized particles range between 10 and 80 nanometers, with the majority falling within the 20–40 nm range, although some larger particles were also observed. The average particle size of the glass-ceramic sample was determined to be 22 nm.
The HRTEM results align well with those obtained from X-ray phase analysis. HRTEM analysis (Figure 6 and Figure 7) identified the presence of cubic LaW2O9 and orthorhombic La2WO6 phases in the sample. The cell parameters were measured as a = 7.33 Å for the cubic phase and a = 8.886 Å, b = 16.555 Å, and c = 5.521 Å for the orthorhombic phase. The corresponding interplanar distances were determined to be d = 3.2 Å and d = 4.4 Å, respectively.

3. Materials and Methods

3.1. Samples Preparation

Glass with the nominal composition 52WO3:22B2O3:26La2O3:0.5Eu2O3 was obtained by applying the conventional melt-quenching method, using commercial powders of reagent-grade WO3 (Merck KGaA, Darmstadt, Germany), H3BO3 (SIGMA-ALDRICH, St. Louis, MO, USA), La2O3 (SIGMA-ALDRICH, St. Louis, MO, USA), and Eu2O3 (SIGMA-ALDRICH, St. Louis, MO, USA) as starting materials. The homogeneous batch (10 g) has been melted for 20 min in air in a platinum crucible at 1240 °C. The glass was obtained by press quenching between two copper plates (cooling rate 102 K/s). To prepare the glass-ceramics (GCs), the precursor glass 52WO3:22B2O3:26La2O3:0.5Eu2O3 was subjected to heat treatment at 680 °C for 3 h, 6 h, 9 h, 15 h, 18 h, and 21 h.

3.2. Samples Characterization

The glass transition (Tg) and crystallization (Tc) temperatures of the glass were determined using differential thermal analysis (Setaram, Labsys Evo 1600, Caluire-et-Cuire, France). The heating rate was 10 K/min in air atmosphere under an air flow of 20 mL/min. X-ray powder patterns of crystallized La2W2O9 glass ceramics were collected on a Bruker D8 Advance diffractometer, Karlsruhe, Germany equipped with a CuKa X-ray source. Monochromatization of the diffracted beam was achieved using a nickel filter in front of a Bruker LynxEye silicon-strip detector. During data collection, a spinner with a rotation speed of 15 rpm was used to average the measurement over the entire volume of the sample. The powder patterns were measured in the angular range of 5.5–80 degrees 2theta with a step of 0.04 degrees 2theta and an acquisition time of 0.4 sec/step per one detector channel. The phase composition of the samples was determined using the Match! v.3.16 program [41] and the ICDD PDF-2 database (2021) [42] as referent files. The program Topas v.4.2 [43] and Pawley fit procedure were used to determine the crystallite size and unit cell parameters of the collected patterns. The TEM observations were carried out using a transmission electron microscope JEM 2100 (JEOL, Tokyo, Japan) with a GATAN Orius 832 SC1000 CCD camera (AMETEK, Berwin, PA, USA) at an accelerating voltage of 200 kV. The specimen for TEM investigation was prepared by grinding the sample in an agate mortar and then disintegrating it in the form of an ethanol suspension by ultrasonic treatment for 6 min. A droplet of the suspension was coated on a standard carbon film on a Cu grid. The size distribution of the particles was performed with the image-processing program ImageJ, and the measurements of the interplanar distances were performed with the specialized software Digital Micrograph (Version 2.31.734). Photoluminescence (PL) excitation and emission spectra at room temperature for all studied samples were measured with a FluoroLog3-22 spectrofluorometer, 2014 (Horiba Jobin-Yvon, Longjumeau, France).

4. Conclusions

Glass-ceramic materials with enhanced photoluminescence emissions were obtained by controlled crystallization of the 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass sample. Structural characterizations, i.e., TEM and XRD, verify the crystalline nature of the resulting glass-ceramics. X-ray studies show that during the heat treatment of the glass, the main crystalline phases are the La2W2O9 cubic phase and orthorhombic La2WO6. Morphological studies revealed that the sample contains spherical and rectangular nanosized particles. The majority of the particles are in the range of 20–40 nm. Photoluminescence spectra revealed that the obtained glass-ceramics can emit red light under excitation at 392 nm originating from the dominant dipole transition 5D0 → 7F2 of Eu3+ ions. Based on the results from the emission spectra, it was established that the formation of La2W2O9:Eu3+ nanocrystals and the appropriate degree of crystallinity are decisive factors for improving the luminescence properties of the samples. Formation of a second crystalline phase, La2WO6, leads to a drop in the emission intensity, because of the redistribution of Eu3+ ions in different crystalline phases. The optical properties confirm that the obtained glass-ceramics are suitable hosts for the incorporation of Eu3+ ions and have potential applications in the field of red light-emitting diodes.

Author Contributions

Conceptualization, R.I., A.Y., and L.A; methodology, A.Y. and L.A.; software, A.Y., L.A., P.T., and P.M.; validation, R.I.; formal analysis, A.Y., L.A., and R.I.; investigation, A.Y., P.T., P.M., P.P., and L.A.; resources, L.A.; data curation, R.I.; writing—original draft preparation, R.I., M.M., L.A., and A.Y.; writing—review and editing, R.I.; visualization, R.I., A.Y., and L.A.; supervision, R.I.; project administration, L.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within this article.

Acknowledgments

Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National roadmap for research infrastructures) supported by the Bulgarian Ministry of Education and Science.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Kumar, K.N.; Vijayalakshmi, L.; Lee, G.; Kang, G.; Lim, J.; Choi, J. Robust color purity of reddish-orange emission from Sm3+-activated La10W22O81 biocompatible microphosphors for solid state lighting and anticancer applications. J. Rare Earths 2023, 41, 1850–1859. [Google Scholar] [CrossRef]
  2. Patout, L.; Jacob, D.; Arab, M.; Pereira de Souza, C.; Leroux, C. Monoclinic Superstructure in Orthorhombic Ce10W22O81 from Transmission Electron Microscopy. Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater. 2014, 70, 268–274. [Google Scholar] [CrossRef] [PubMed]
  3. Pier, T.; Jüstel, T. Application of Eu(III) activated tungstates in solid state lighting. Opt. Mater. 2024, X22, 100299. [Google Scholar] [CrossRef]
  4. Cheng, Q.; Ren, F.; Lin, Q.; Tong, H.; Miao, H. High quantum efficiency red emitting alpha-phase La2W2O9: Eu3+phosphor. J. Alloys Compd. 2019, 772, 905–911. [Google Scholar] [CrossRef]
  5. Song, K.; Li, G. Electrospinning synthesis, characterization and luminescence properties of La2W2O9: Eu3+ nanofibers. J. Mater. Sci. Mater. Electron. 2015, 27, 1227–1231. [Google Scholar] [CrossRef]
  6. Zhang, J.; Yang, Y.; Yu, F.; Liu, Y.; Han, B.; Chao, M.; Liu, L. Synthesis and Luminescence Properties of La2W2O9:Eu3+ Micron-Crystals. J. Nanosci. Nanotechnol. 2016, 16, 3852–3856. [Google Scholar] [CrossRef]
  7. Baby, B.; Thomas, S.; Jose, J.; Gopinath, M.; Biju, P.R.; Joseph, C. Spectroscopic analysis of La2(WO4)3:Tb3+ phosphor and the delayed concentration quenching of 5D4 →7FJ emission. J. Lumin. 2025, 277, 120895. [Google Scholar] [CrossRef]
  8. Naveen Kumar, K.; Vijayalakshmi, L.; Hwang, P.; Wadhwani, A.; Choi, J. Bright red-luminescence of Eu3+ion-activated La10W22O8 microphosphors for noncytotoxic latent fingerprint imaging. J. Alloys Compd. 2020, 840, 155589. [Google Scholar] [CrossRef]
  9. Fedorov, P.P.; Luginina, A.A.A.; Popov, I. Transparent oxyflouride glas ceramics. J. Fluor. Chem. 2015, 172, 22–50. [Google Scholar] [CrossRef]
  10. Erth, D. Photoluminescenec in Glass and Glass Ceramics. IOP Conf. Ser. Mater. Sci. Eng. 2009, 2, 012001. [Google Scholar]
  11. Ferrari, M.; Righini, G.C. Glass-ceramic materials for guided-waste optics. Int. J. Appl. Sci. 2015, 6, 240–248. [Google Scholar]
  12. Aleksandrov, L.; Iordanova, R.; Dimitried, Y.; Geogiev, N.; Komatsu, T. Eu3+ doped 1La2O3:2WO3:1B2O3 glass and glass-ceramic. Opt. Mater. 2014, 26, 1366–1372. [Google Scholar] [CrossRef]
  13. Aleksandrov, L.; Komatsu, T.; Iordanova, R.; Dimitried, Y. Raman spectroscopic study of structure of WO3-La2O3-B2O3 glasses with no color and crystallization of LaBWO6. Opt. Mater. 2011, 34, 201–206. [Google Scholar] [CrossRef]
  14. Jurinski, B.; Lisanova, G. Compounds of rare earth elements with mixed oxyanions: Synthesis, structure, boundaries of existence in the series La-Lu. J. Inorg. Chem. 1998, 43, 2064–2074. [Google Scholar]
  15. Collado, J.A.; Aranda, M.A.G.; Cabeza, A.; Olivera-Pastor, P.; Bruque, S. Synthesis, structures, and thermal expansion of the La2W2− xMoxO9 series. J. Solid State Chem. 2002, 167, 80–85. [Google Scholar] [CrossRef]
  16. Goutenoire, F.; Isnard, O.; Retoux, R.; Lacorre, P. Crystal Structure of La2Mo2O9, a New Fast Oxide−Ion Conductor. Chem. Mater. 2000, 12, 2575–2580. [Google Scholar] [CrossRef]
  17. Yoshimura, M.; Rouanet, A. High temperature phase relation in the system La2O3-WO3. Mater. Res. Bull. 1976, 11, 151–158. [Google Scholar] [CrossRef]
  18. Marrero-López, D.; Peña-Martínez, J.; Ruiz-Morales, J.C.; Núñez, P. Phase stability and ionic conductivity in substituted La2W2O9. J. Solid State Chem. 2008, 181, 253–262. [Google Scholar] [CrossRef]
  19. Binnemans, K. Interpretation of europium (III) spectra. Coord. Chem. Rev. 2015, 295, 1–45. [Google Scholar] [CrossRef]
  20. Blasse, G.; Grabmaier, B.C. Luminescent Materials, 1st ed.; Springer: Berlin/Heidelber, Germany, 1994; pp. 18–29. [Google Scholar]
  21. Hoefdraad, H.E. The charge-transfer absorption band of Eu3+ in oxides. J. Solid State Chem. 1975, 15, 175–177. [Google Scholar] [CrossRef]
  22. Parchur, A.K.; Ningthoujam, R.S. Behaviour of electric and magnetic dipole transitions of Eu3+, 5D0-7F0 and Eu-O charge transfer band in Li+ co-doped YPO4:Eu3+. RSC Adv. 2012, 2, 10859–10868. [Google Scholar] [CrossRef]
  23. Mariselvam, K.; Liu, J. Synthesis and luminescence properties of Eu3+ doped potassium titano telluroborate (KTTB) glasses for red laser applications. J. Lumin. 2021, 230, 117735. [Google Scholar] [CrossRef]
  24. Dutta, P.S.; Khanna, A. Eu3+ activated molybdate and tungstate based red phosphors with charge transfer band in blue region. ECS J. Solid State Sci. Technol. 2013, 2, R3153–R3167. [Google Scholar] [CrossRef]
  25. Thieme, C.; Herrmann, A.; Kracker, M.; Patzig, C.; Hoche, T.; Russel, C. Microstructure investigation and fluorescence properties of Europium-doped scheelite crystals in glass-ceramics made under different synthesis conditions. J. Lumin. 2021, 238, 118244. [Google Scholar] [CrossRef]
  26. Bunzli, J.C.G. Lanthanide luminescence: From a mystery to rationalization, understanding, and applications. In Handbook on the Physics and Chemistry of Rare Earths; Elsevier: Amsterdam, The Netherlands, 2016; Volume 50, pp. 141–176. [Google Scholar]
  27. Fu, J.; Kobayashi, M.; Sigimoto, S.; Parker, J.M. Scintillation from Eu2+ in Nanocrystallized Glass. J. Am. Ceram. Soc. 2009, 92, 2019–2021. [Google Scholar] [CrossRef]
  28. Shigeo, S.; William, M. Phosphor Handbook; CRC Press: Washington, DC, USA, 1998. [Google Scholar]
  29. Iordanova, R.; Milanova, M.; Yordanova, A.; Aleksandrov, L.; Nedylkov, N.; Kukeva, R.; Petrova, P. Structure and Luminescent Properties of Niobium Modified ZnO-B2O3: Eu3+ Glass. Materials 2024, 17, 1415. [Google Scholar] [CrossRef]
  30. Milanova, M.; Aleksandrov, L.; Yordanova, A.; Iordanova, R.; Tagiara, N.S.; Herrmann, A.; Gao, G.; Wondraczek, L.; Kamitsos, E.I. Structural and luminescence behavior of Eu3+ ions in ZnO-B2O3-WO3 glasses. J. Non-Cryst. Solids 2023, 600, 122006. [Google Scholar] [CrossRef]
  31. Aleksandrov, L.; Milanova, M.; Yordanova, A.; Iordanova, R.; Nedyalkov, N.; Petrova, P.; Tagiara, N.S.; Palles, D.; Kamitsos, E.I. Synthesis, structure and luminescence properties of Eu3+-doped 50ZnO.40B2O3.5WO3.5Nb2O5 glass. Phys. Chem. Glas. Eur. J. Glass Sci. Technol. B 2023, 64, 101–109. [Google Scholar]
  32. Narro-García, R.; Desirena, H.; López-Luke, T.; Guerrero-Contreras, J.; Jayasankar, C.K.; Quintero-Torres, R.; De la Rosa, E. Spectroscopic properties of Eu3+/Nd3+ co-doped phosphate glasses and opaque glass–ceramics. Opt. Mater. 2015, 46, 34–39. [Google Scholar] [CrossRef]
  33. Aleksandrov, L.; Yordanova, A.; Milanova, M.; Iordanova, R.; Tzvetkov, P.; Markov, P.; Petrova, P. Glass Ceramic Materials with Luminescent Properties in the System ZnO-B2O3-Nb2O5-Eu2O3. Molecules 2024, 29, 3452. [Google Scholar] [CrossRef]
  34. Dwivedi, A.; Joshi, C.; Rai, S.B. Effect of heat treatment on structural, thermal and optical properties of Eu3+ doped tellurite glass: Formation of glass-ceramic and ceramics. Opt. Mater. 2015, 45, 202–208. [Google Scholar] [CrossRef]
  35. Laia, A.S.; Maciel, G.S.; Rodrigues, J.J., Jr.; Dos Santos, M.A.; Machado, R.; Dantas, N.O.; Silva, A.C.A.; Rodrigues, R.B.; Alencar, M.A. Lithium-boron-aluminum glasses and glass-ceramics doped with Eu3+: A potential optical thermometer for operation over a wide range of temperatures with uniform sensitivity. J. Alloys Compd. 2022, 907, 164402. [Google Scholar] [CrossRef]
  36. Muniz, R.F.; De Ligny, D.; Sandrini, M.; Zanuto, V.S.; Medina, A.N.; Rohling, J.H.; Guyot, Y. Fluorescence line narrowing and Judd-Ofelt theory analyses of Eu3+-doped low-silica calcium aluminosilicate glass and glass-ceramic. J. Lumin. 2018, 201, 123–128. [Google Scholar] [CrossRef]
  37. Smentek, L.; Kȩdziorski, A. f ↔ f electric dipole transitions; old problems in a new light. J. Alloys Compd. 2009, 488, 586–590. [Google Scholar] [CrossRef]
  38. Binnemans, K.; Gorller-Walrand, C. Application of the Eu3+ ion for site symmetry determination. J. Rare Earths 1996, 14, 173–180. [Google Scholar]
  39. Paolini, T.B. SpectraChroma, Version 1.0.1, Computer Software; Zenodo: Geneva, Switzerland, 2021. Available online: https://zenodo.org/records/4906590 (accessed on 7 June 2021).
  40. Trond, S.S.; Martin, J.S.; Stanavage, J.P.; Smith, A.L. Properties of Some Selected Europium—Activated Red. J. Electrochem. Soc. 1969, 116, 1047–1050. [Google Scholar] [CrossRef]
  41. Putz, H.; Brandenburg, K. Match!—Phase Analysis Using Powder Diffraction, Version 4; Crystal Impact—GbR: Bonn, Germany. Available online: https://www.crystalimpact.de/match (accessed on 9 September 2024).
  42. International Centre for Diffraction Data. Available online: www.ICDD.com (accessed on 9 September 2024).
  43. Bruker AXS.TOPAS V4. General Profile and Structure Analysis Software for Powder Diffraction Data—User’s Manual; Bruker AXS: Karlsruhe, Germany, 2008. [Google Scholar]
Molecules 30 00832 g001
Figure 1. DTA curves of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass.
Figure 1. DTA curves of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass.
Molecules 30 00832 g001
Molecules 30 00832 g002
Figure 2. XRD patterns of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass ceramics crystallized at 680 °C with different durations. Indexed peaks represent the La2W2O9 cubic phase. For comparison, vertical red bars correspond to Bragg peaks of β-La2W1.7Mo0.3O9. Asterisk (*) represents the most intensive (312) peak of orthorhombic La2WO6 (PDF # 00-057-1075).
Figure 2. XRD patterns of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass ceramics crystallized at 680 °C with different durations. Indexed peaks represent the La2W2O9 cubic phase. For comparison, vertical red bars correspond to Bragg peaks of β-La2W1.7Mo0.3O9. Asterisk (*) represents the most intensive (312) peak of orthorhombic La2WO6 (PDF # 00-057-1075).
Molecules 30 00832 g002
Molecules 30 00832 g003
Figure 3. Excitation spectra of 0.5% Eu3+-doped 52WO3:22B2O3:26La2O3 glass and glass-ceramic samples.
Figure 3. Excitation spectra of 0.5% Eu3+-doped 52WO3:22B2O3:26La2O3 glass and glass-ceramic samples.
Molecules 30 00832 g003
Molecules 30 00832 g004
Figure 4. Emission spectra of 0.5% Eu3+-doped 52WO3:22B2O3:26La2O3 glass and glass-ceramic samples.
Figure 4. Emission spectra of 0.5% Eu3+-doped 52WO3:22B2O3:26La2O3 glass and glass-ceramic samples.
Molecules 30 00832 g004
Molecules 30 00832 g005
Figure 5. CIE chromaticity diagram of Eu3+-doped 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and corresponding glass-ceramics.
Figure 5. CIE chromaticity diagram of Eu3+-doped 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and corresponding glass-ceramics.
Molecules 30 00832 g005
Molecules 30 00832 g006
Figure 6. Bright field micrograph (a) and HRTEM (b) of nanosized particles of La2W2O9.
Figure 6. Bright field micrograph (a) and HRTEM (b) of nanosized particles of La2W2O9.
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Molecules 30 00832 g007
Figure 7. Bright field micrograph (a) and HRTEM (b) of La2W2O9 and La2WO6.
Figure 7. Bright field micrograph (a) and HRTEM (b) of La2W2O9 and La2WO6.
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Molecules 30 00832 g008
Figure 8. Bright field micrograph (a) and particle size distribution (b) of GC-18 h.
Figure 8. Bright field micrograph (a) and particle size distribution (b) of GC-18 h.
Molecules 30 00832 g008
Table 1. Unit cell parameters and crystallite size of La2W2O9 cubic phase (SG. P213) after thermal treatment at 680 °C.
Table 1. Unit cell parameters and crystallite size of La2W2O9 cubic phase (SG. P213) after thermal treatment at 680 °C.
Crystallized
at 680 °C		Unit Cell
Parameter [Å]		Crystallite
Size [nm]
3 h7.134(1)27.8(6)
6 h7.118(2)17.9(5)
9 h7.132(1)26.6(4)
12 h7.131(1)23.9(3)
15 h7.1187(2)22.1(3)
18 h7.117(1)22.1(4)
21 h7.119(1)23.3(4)
Table 2. Relative luminescent intensity ratio (R) of the two transitions (5D0 → 7F2)/(5D0 → 7F1) for 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and glass-ceramics heat treated at different time durations and of other reported Eu3+-doped oxide glasses and glass-ceramics.
Table 2. Relative luminescent intensity ratio (R) of the two transitions (5D0 → 7F2)/(5D0 → 7F1) for 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and glass-ceramics heat treated at different time durations and of other reported Eu3+-doped oxide glasses and glass-ceramics.
Glass CompositionRelative Luminescent Intensity Ratio, RReference
Glass 52WO3:22B2O3:26La2O3:0.5Eu2O34.88Current work
GC-3 h4.93Current work
GC-6 h5.58Current work
GC-9 h5.83Current work
GC-12 h5.88Current work
GC-15 h5.95Current work
GC-18 h6.12Current work
GC-21 h5.92Current work
Glass 50ZnO:(50-x)B2O3: xNb2O5:0.5Eu2O3:, x = 0, 1, 3 and 5 mol%4.31–5.16[29]
Glass 50ZnO:40B2O3:10WO3:xEu2O3 (0 ≤ x ≤ 10)4.54 ÷ 5.77[30]
Glass 50ZnO:40B2O3:5WO3:5Nb2O5:xEu2O3 (0 ≤ x ≤ 10)5.09 ÷ 5.76[31]
Glass 66P2O5–10.5Al2O3–3.05BaO–16.5K2CO3–0.7NaF–xEu2O3–0.5Nd2O3–(2.75-x) La2O3 (mol.%), where x = 0, 0.25, 0.5, 0.75, 1.5 and 23.72[32]
Glass-ceramic 66P2O5–10.5Al2O3–3.05BaO–16.5K2CO3–0.7NaF–xEu2O3–0.5Nd2O3–(2.75-x) La2O3 (mol.%), where x = 0, 0.25, 0.5, 0.75, 1.5 and 24.72
Glass 50ZnO:47B2O3:3Nb2O5:0.5Eu2O35.16[33]
Glass-ceramic 50ZnO:47B2O3:3Nb2O5:0.5Eu2O35.21–5.49
Glass 74.0 TeO2+25.0 Li2CO3+1.0 Eu2O33.70[34]
Glass-ceramic 74.0 TeO2+25.0 Li2CO3+1.0 Eu2O33.65
Glass 50Li2O·45B2O3·5Al2O3: 2Eu2O33.91[35]
Glass ceramic 50Li2O·45B2O3·5Al2O3: 2Eu2O34.047
Glass 7SiO2-47.4CaO-40.5Al2O3-4.1MgO-1Eu2O34.58[36]
Glass-ceramic 7SiO2-47.4CaO-40.5Al2O3-4.1MgO-1Eu2O31.97
Table 3. CIE chromaticity coordinates of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and glass-ceramics.
Table 3. CIE chromaticity coordinates of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass and glass-ceramics.
Glass CompositionChromaticity Coordinates (x, y)
Glass 52WO3:22B2O3:26La2O3:0.5Eu2O30.629, 0.328
GC-3 h0.650, 0.343
GC-6 h0.648, 0.345
GC-9 h0.651, 0.345
GC-12 h0.651, 0.345
GC-15 h0.650, 0.346
GC-18 h0.650, 0.346
GC-21 h0.651, 0,346
NTSC standard for red light0.670, 0.330
Y2O2S:Eu3+0.658, 0.340
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Yordanova, A.; Milanova, M.; Aleksandrov, L.; Iordanova, R.; Tzvetkov, P.; Markov, P.; Petrova, P. Preparation of Glass-Ceramic Materials by Controlled Crystallization of Eu2O3-Doped WO3-B2O3-La2O3 Glasses and Their Luminescent Properties. Molecules 2025, 30, 832. https://doi.org/10.3390/molecules30040832

AMA Style

Yordanova A, Milanova M, Aleksandrov L, Iordanova R, Tzvetkov P, Markov P, Petrova P. Preparation of Glass-Ceramic Materials by Controlled Crystallization of Eu2O3-Doped WO3-B2O3-La2O3 Glasses and Their Luminescent Properties. Molecules. 2025; 30(4):832. https://doi.org/10.3390/molecules30040832

Chicago/Turabian Style

Yordanova, Aneliya, Margarita Milanova, Lyubomir Aleksandrov, Reni Iordanova, Peter Tzvetkov, Pavel Markov, and Petia Petrova. 2025. "Preparation of Glass-Ceramic Materials by Controlled Crystallization of Eu2O3-Doped WO3-B2O3-La2O3 Glasses and Their Luminescent Properties" Molecules 30, no. 4: 832. https://doi.org/10.3390/molecules30040832

APA Style

Yordanova, A., Milanova, M., Aleksandrov, L., Iordanova, R., Tzvetkov, P., Markov, P., & Petrova, P. (2025). Preparation of Glass-Ceramic Materials by Controlled Crystallization of Eu2O3-Doped WO3-B2O3-La2O3 Glasses and Their Luminescent Properties. Molecules, 30(4), 832. https://doi.org/10.3390/molecules30040832

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