Margarita Milanova

In this study, the influences of WO₃ on the structure, thermal behavior and luminescent characteristics of Eu³⁺-doped borosilicate glasses with compositions (35 − x/2)B₂O₃:(35 − x/2)SiO₂:25La₂O₃:5CaO:0.5Eu₂O₃:xWO₃, x = 0, 5, 10, and 15 mol% have been studied via X-ray and neutron diffraction (XRD, ND) combined with reverse Monte Carlo (RMC) modeling, infrared spectroscopy (IR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy and density measurements. IR and RMC structural modeling reveal that the glass network consists of SiO₄ tetrahedra with non-bridging oxygen (Q²); diborate, pyroborate and metaborate units; [WO₄]²⁻ and WO₆ groups; and Si-O-W, Si-O-B, B-O-B and W-O-W linkages. Structural and density analyses show that incorporating up to 10 mol% WO₃ increases structural disorder, depolymerizes the silicate matrix, and creates non-bridging oxygens (NBOs). In contrast, at 15 mol% WO₃, the network exhibits crosslinking due to the development of interconnected, polymerized WO₆ octahedra. Thermal investigations demonstrate exceptionally high glass transition temperatures (T_g > 700 °C) and notable thermal stability, as no crystallization occurred up to 800 °C in any sample. The slight decrease in T_g to 718 °C at 15 mol% WO₃ validates network “softening” driven by the formation of polymerized WO₆ octahedral structural units. Photoluminescence spectra showed a strong red emission at 612 nm from the ⁵D₀→⁷F₂ transition of Eu³⁺ under near-UV (392 nm) excitation. It was established that the addition of WO₃ to borosilicate glasses leads to improvement of the emission properties of the active ion through structural modification. These results demonstrate that the optimized glass compositions hold potential for use as red phosphor materials.

Glasses with compositions (52.5 − x/2)B₂O₃:(12.5 − x/2)SiO₂:25La₂O₃:5ZnO:5CaO:0.5Eu₂O₃:xWO₃, x = 0, 2.5, 5, 7.5, 10, 20 (mol%) were prepared by conventional melt-quenching method and investigated by X-ray diffraction analysis, DSC analysis, DR-UV-Vis spectroscopy and photoluminescence spectroscopy. Physical parameters like density, molar volume, oxygen molar volume and oxygen packing density were also determined. Their values, as well as DR-UV-Vis spectroscopy results, indicate that the tungstate ions incorporate into the base borosilicate glass as tetrahedral WO₄ and octahedral WO₆ groups. With increasing WO₃ content over 5 mol%, WO₆ units are progressively linked to each other by W-O-W bonds, leading to the formation of a more connected and homogeneous glass network. Glasses are characterized by a high glass transition temperature (over 650 °C) and good thermal stability. The emission intensity of the Eu³⁺ ion increases with the introduction of WO₃ due to the occurrence of non-radiative energy transfer from the tungstate groups to the active ion. The most intense luminescence peak observed at 612 nm suggests that the glasses are potential materials for red emission.

Glasses with compositions 52.5B₂O₃:12.5SiO₂:25La₂O₃:5CaO:5ZnO:0.5Eu₂O₃ and50B₂O₃:10SiO₂:25La₂O₃:5CaO:5ZnO:5WO₃:0.5Eu₂O₃ (mol%) were prepared by conventional melt-quenching method and investigated by X-ray diffraction analyses, DSC analysis, DR-UV-Vis spectroscopy and photoluminescence spectroscopy. Physical properties like density, molar volume, oxygen molar volume and oxygen packing density were also determined. Glasses are characterized with high glass transition temperature (over 650 °C). DR-UV-Vis spectroscopy results indicate that the tungstate ions incorporate into the base borosilicate glass as tetrahedral WO₄ groups. The lower band gap energy values show that the introduction of WO₃ into the base borosilicate glass increases the number of non-bridging oxygen species in the glass structure. The emission intensity of the Eu³⁺ ion increases with the introduction of WO₃ due to the occurrence of non-radiative energy transfer from the tungstate groups to the active ion. The most intense luminescence peak observed at 612 nm suggest that the glasses are potential materials for red emission.

Applying the melt quenching method (cooling rate 10¹–10² K/s), new multicomponent vanadate glasses were synthesized, containing different amounts of MoO₃ at the expense of B₂O₃ with the composition 20Li₂O:(30 − x)B₂O₃:50V₂O₅:xMoO₃, x = 10, 20 mol%. The obtained samples were characterized by X-ray diffraction, infrared spectroscopy, differential scanning calorimetry and impedance spectroscopy. The density of the glasses was measured by the Archimedes method, on the basis of which the physicochemical parameters molar volume, oxygen molar volume and oxygen packing density were calculated. It was found that the replacement of B₂O₃ with MoO₃ leads to changes in electrical conductivity, which are a consequence of the increase in non-bridging oxygen atoms in the amorphous structure. The electrochemical characterization of the 20Li₂O:(30 − x)B₂O₃:50V₂O₅:20MoO₃ glass obtained was performed by assembling an all-solid-state cell, employing 20Li₂O:(30 − x)B₂O₃:50V₂O₅:20MoO₃ glass as a cathode active material. The obtained results show that the studied glass compositions are interesting in view of their potential application as cathode materials in all-solid-state lithium-ion batteries.

Applying the melt quenching method (cooling rate 101-102K/s), new multicomponent vanadate glasses were synthesized, containing different amounts of MoO3 at the expense of B2O3 with the composition 20Li2O:(30-х)B2O3:50V2O5:xMoO3, x = 10, 20 mol%. The obtained samples were characterized by X-ray diffraction, infrared spectroscopy, differential scanning calorimetry and impedance spectroscopy. The density of the glasses was measured by the Archimedes method, on the basis of which the physicochemical parameters molar volume, oxygen molar volume and oxygen packing density were calculated. It was found that the replacement of B2O3 with MoO3 leads to changes in electrical conductivity, which are a consequence of the increase in non-bridging oxygen atoms in the amorphous structure. The electrochemical characterization of the 20Li2O:(30-х)B2O3:50V2O5:20MoO3 glass obtained was performed by assembling an all-solid-state cell, employing 20Li2O:(30-х)B2O3:50V2O5:20MoO3 glass as a cathode active material. The obtained results show that the studied glass composition is interesting in view of their potential application as cathode materials in all-solid-state lithium-ion batteries.

Dy³⁺ single-doped and Dy³⁺/Eu³⁺ co-doped ZnO:B₂O₃:WO₃:Nb₂O₅ glass was successfully synthesized using the melt quenching method. The amorphous character of the prepared samples was confirmed by X-ray diffraction (XRD). The glass transition and crystallization temperatures were examined by differential scanning calorimetry (DSC). Raman spectroscopy was applied to investigate the glass microstructure. Physical properties like the density, molar volume, oxygen molar volume and oxygen packing density of the glass were also determined. The photoluminescence excitation (PLE) and emission (PL) spectra of the resultant glass types were measured. The obtained Dy³⁺ single-doped glass was characterized by strong luminescence at 482 and 574 nm, corresponding to the ⁴F_9/2 → ⁶H_15/2 (blue) and ⁴F_9/2 → ⁶H_13/2 (yellow) transitions, respectively, and weak luminescence at 663 nm and 753 nm due to the ⁴F_9/2 → ⁶H_11/2 (red) and ⁴F_9/2 → ⁶H_9/2 + ⁶F_11/2 (red) transitions. The luminescence results indicate that energy transfer from the Dy³⁺ to Eu³⁺ ions occurs in the proposed glass system. The emitted light from the Dy³⁺ single-doped glass was found to be yellow-orange. The Dy³⁺/Eu³⁺ co-doped samples emitted darker orange light. The obtained results show that the investigated types of glass have the potential to be used as orange light-emitting materials.

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.

In this paper, the crystallization behavior of 52WO3:22B2O3:26La2O3:0.5Eu2О3 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. It was established that the optimum emission intensity is registered for glass-ceramic samples obtained after 18 h heat treatment of the parent glass.

Novel multicomponent glasses with nominal compositions of (50−x)MoO₃:xWO₃:25La₂O₃:25B₂O₃, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % Eu₂O₃ were prepared using a conventional melt-quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. The optical properties of the glasses were investigated by UV–vis absorption spectroscopy and a determination of the refractive index. Physical parameters such as density, molar volume, oxygen molar volume and oxygen packing density were determined. The glasses are characterized by a high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO₄)²⁻ and (WO₄)²⁻ units providing Raman bands of around 317 cm⁻¹, 341–352 cm⁻¹, 832–820 cm⁻¹ and 928–935 cm⁻¹. At the same time, with the replacement of MoO₃ with WO₃ some fraction of WO₆ octahedra are produced, the number of which increases with the increasing WO₃ content. A strong red emission from the ⁵D₀ level of Eu³⁺ ions was registered under near-UV (397 nm) excitation using the ⁷F₀ → ⁵L₆ transition of Eu³⁺. Photoluminescence (PL) emission gradually increases with increasing WO₃ content, evidencing that WO₃ is a more appropriate component than MoO₃. The integrated fluorescence intensity ratio R (⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu³⁺ in non-centrosymmetric sites. All findings suggest that the investigated glasses are potential candidates for red light-emitting phosphors.

A novel multicomponent glasses with nominal compositions of (50-x)MoO3:xWO3:25La2O3:25B2O3, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % Eu2O3 were prepared using a conventional melt quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. Physical parameters as density, molar volume, oxygen molar volume and oxygen packing density were determined. Glasses are characterized with high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO4)2- and (WO4)2- units providing Raman bands of around 317 cm-1, 341-352 cm-1, 832-820 cm-1 and 928-935 cm-1. At the same time with the replacement of MoO3 with WO3 some fraction of WO6 octahedra are produced, which number increases with the increasing WO3 content. A strong red emission from the 5D0 level of Eu3+ ions was registered under near UV (395 nm) excitation using the 7F0 →5L6 transition of Eu3+. PL emission gradually increases with increasing WO3 content evidencing that WO3 is more appropriate component than MoO3. The integrated fluorescence intensity ratio R (5D0 →7F2/5D0 →7F1) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu3+ in non-centrosymmetric sites.