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A Novel Eu3+ Doped Glasses in the MoO3‐WO3‐La2O5‐ B2O3 System: Preparation, Structure and Photoluminescent Properties

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30 August 2024

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03 September 2024

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Abstract
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.
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Subject: Chemistry and Materials Science  -   Electronic, Optical and Magnetic Materials

1. Introduction

Trivalent europium doped materials are usually considered as good red-emitting phosphor candidates for LEDs. Its characteristic energy transfer generates a strong emission with a high color purity [1]. Unfortunately,Eu3+-doped materials cannot be efficiently excited by the present LED chips, because its excitation peaks are weak in nature due to parity-forbidden f–f transitions [2]. The use of the inorganic host matrices with strong absorption in the ultraviolet (UV) region, which occurs commonly via excitation under Ligand-to-Metal Charge Transfer (LMCT) absorption bands, is a usual approach to improve the luminescence intensities from the Eu3+ materials [3]. Among many inorganic compounds, molybdates and tungstate phases are widely studied for decades as hosts for lanthanide doping due to their absorption in the mid ultraviolet region via O(2p) → W(5d)/Mo(4d) charge transfer and subsequent transfer of the energy to the low-lying emissive states of trivalent lanthanide ions [3,4]. At the present, the reports are mainly focused on the preparation of the crystalline molybdate and tungstate host structures, while data for the molybdate and tungstate glass and glass ceramic rare earth hosts are limited [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. Compared with bulk crystalline hosts, glasses have the advantages of easy fabrication, low cost, high mechanical strength, and high chemical durability. Therefore, it is meaningful to prepare molybdate and tungstate glass compositions doped with rare earth activators and to investigate their luminescence.
In our previous works we have reported the preparation of Eu3+ doped glasses and glass ceramics with a high WO3 content in the systems WO3:La2O3:B2O3 and WO3:La2O3:B2O3:Nb2O5 possessing strong 613 nm red luminescence with excitation at 390 nm, that is an indication they could be promising materials for red-light source. [17,18]. In our more recent works, we have obtained tungsten-containing ZnO–B2O3 glasses doped with Eu3+ active ion and we have studied their luminescent properties [19,20,21]. The obtained results from glass structure, physical, thermal, and optical properties indicate the suitability of the 50ZnO:40B2O3:10WO3 glass network for the luminescence performance of Eu3+ ions. The positive effect of the addition of WO3 on the luminescence intensity is proven by the stronger Eu3+ emission of the zinc–borate glass containing WO3 compared to the WO3-free zinc–borate glass, a phenomenon engendered mainly by the energy transfer from tungstate groups to the Eu3+ ions (sensitizing effect). The most intense luminescence peak observed at 612 nm and the high-integrated emission intensity ratio (R) of the 5D0 → 7F2/ 5D0 → 7F1 transitions at 612 nm and 590 nm of 5.77 suggest that the glasses have the potential for red emission materials. We have also prepared a homogeneous optically transparent ternary MoO3-La2O3-B2O3 and WO3-La2O3-B2O3 glasses containing a large amount of MoO3 (10-50 mol%) and WO3 (15 – 50 mol% ) and as well as quaternary glasses with nominal compositions of (50-x)MoO3:xWO3:25La2O3:25B2O3, x = 0, 10, 20, 30, 40, 50 mol% and we have investigated their structure and crystallization behavior [22,23,24]. It was proposed that the glass structure of ternary and quaternary glasses is built up mainly from tetrahedral (MoO4)2- and (WO4)2- units and BO3 and BO4 groups. The main crystalline phases in the crystallized MoO3-La2O3-B2O3 glasses were found to be LaMoBO6 and LaB3O6. The formation of LaMox-1WxO6 solid solutions was confirmed in the crystallized samples from MoO3-WO3-La2O3-B2O3 system.
In this paper we continue our investigations over glasses in the MoO3-WO3-La2O3-B2O3 system. The purpose is to obtained Eu3+ doped glasses with nominal compositions of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x = 0, 10, 20, 30,40,50 mol% and to study their thermal behavior, structure and luminescent properties.

2. Results and Discussion

2.1. Thermal analysis

The DTA curves of the (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses are shown on Figure 1.
The endothermic dips corresponding to the glass transition temperature (Tg) and the exothermic peaks due to the crystallization temperature (Tc) are observed. The values of Tg and Tc estimated are pointed out on the figure. As it is seen the glass transition temperature increase from 577 °C to 616 °C with the substitution of WO3 for MoO3 because of the replacement of weaker Mo-O bonds with a stronger W-O bonds [24]. In the DTA curves of glasses with a higher MoO3 content (x = 0 and x = 10) two broad exothermic peaks are observed, while glasses with a higher WO3 content (x = 50 and x= 40) are characterized with one sharp and intensive exothermic effect, evidencing different crystallization behavior depending on the compositions. The x = 0 glass has higher thermal stability against crystallization i. e. ΔT = Tc-Tg = 125 °C compared to the ΔT of x =50 glass (83°C) evidencing better glass forming ability of molybdate than tungstate glass. On the other hand glasses containing higher amount of MoO3 and lower WO3 content up to 20 mol% have the highest ΔT values (145°C for glass x = 10 and 137°C for glass x= 20), indicating that the addition of a small amount WO3 into the molybdate glass improves glass formation tendency of the compositions.

2.2. Structural investigations

2.2.1. Raman analysis

Raman spectra of (50-x) MoO3:xWO3:25La2O5:25B2O3:3Eu3+ (x=0, 10, 20, 30, 40, 50 mol%) glasses are shown in Figure 2. All spectra consist of broad Raman bands at around 317 cm-1, 341-352 cm-1, 832-820 cm-1 and 928-935 cm-1. The spectra obtained are similar with the spectra of four component glasses (50-x)MoO3:xWO3:25La2O5:25B2O3 , x=10, 20, 30, 40, 50 and three component xMoO3:25La2O3:(75-x)B2O3, x= 10-50 and xWO3:25La2O3:(75-x)B2O3, x=15, 25, 50 glasses previously reported and discussed by us in detail in the ref [22,23,24].
Based on these former data, we can assigned the Raman bands obtained as follows. The most intense band at 928-935 cm-1 is ascribed to the symmetric stretching vibration mode ν1 of isolated (MoO4)2- and (WO4)2- tetrahedral units. As it is seen from the Figure 2, this band became broader with an increasing WO3 content. Spectral deconvolution performed in ref. [22,23,24] has shown the presence of weak band at 980-996 cm-1 related to WO6 octahedral groups in WO3-containing glasses. The band at 832-820 cm-1 is due to the asymmetric ν3 stretching vibration of (MoO4)2- and (WO4)2- groups. Two Raman bands at low frequency spectral region at 315 cm-1and 341-352 cm-1are interpreted as the symmetric bending mode ν2 of (MoO4)2- and (WO4)2- tetrahedral units, that overlap with the Eu-O vibration and vibration of LnOn units respectively [20,22,23,24]. In the Raman spectra obtained there are no any peaks in the region of 1000-1500 cm-1, where Raman bands of the boron oxygen groups are situated [20]. However, having in mind our previous works over similar glass compositions [22,23,24], it could be suggested that BO3 and BO4 groups and B-O-B bonds are also present in the structure of the investigated glasses. The spectral results obtained suggest that the structure of (50-x)MoO3:xWO3:25La2O5:25B2O3:3Eu3+ (x=0, 10, 20, 30, 40, 50 mol%) glasses consists of mainly (MoO4)2- and (WO4)2- tetrahedral units which fraction changes continuously with the substitution of WO3 for MoO3. At the same time with the replacement of MoO3 with WO3 some amount of WO6 octahedra are produced, which number increases with the increasing WO3 content.

2.2.2. Physical parameters

A structural information of glasses was also gain by density (ρg) measurement on which base the values of several physical parameters as: molar volume (Vm), oxygen molar volume (Vo) and oxygen packing density (OPD) are evaluated, using the following relations:
V m = ∑ x i M i ρ g
V o = V m × 1 ∑ x i n i
O P D = 1000 × C × ρ g M
where xi is the molar fraction of each component i, Mi the molecular weight, ρg the glass density and ni is the number of oxygen atoms in each oxide, C is the number of oxygen per formula units, and M is the total molecular weight of the glass compositions. The values obtained are listed in Table 1. As it is seen from the table, the density increases with the increasing WO3 content at the expense of MoO3 because of the replacement of lighter MoO3 (molecular weight 143.94 g/mol) with heavier WO3 (molecular weight 231.84 g/mol). The Vm and Vo values of glasses decrease, while their OPD values become greater with the gradual replacement of MoO3 with WO3 evidencing better packing and bonding in the glass network, with the introduction of WO3 [25].
It was found in our earlier paper that WO6 and W-O-W bridging bonds are formed in the glass network of (50-x)MoO3:xWO3:25La2O3:25B2O3 , x=10, 20, 30, 40, 50 and xWO3:25La2O3:(75-x)B2O3, x= 15, 25, 50 glasses [23,24]. The presence of bridging oxygens generates more connected glass structure, resulting in increase in the density and OPD and decrease in molar volume observed. The almost linear relationship between the density, physical parameters established and WO3 content suggests an increasing number of WO6 and their gradual polymerization (i. e. formation of W-O-W bonds) with WO3 loading.

2.2.3. Optical studies

The optical absorption spectra at room temperature of (50-x) MoO3:xWO3:25La2O5:25B2O3:3Eu3+ (x=0, 10, 20, 30, 40, 50 mol%) glasses are shown in Figure 3. The absorption edge of ternary glasses, containing only MoO3 or WO3 (x = 0 and x = 50 respectively) shifts to the lower wavelength value in the UV range as compared with glasses containing both MoO3 and WO3. For instance, the absorption edge of glass x = 50 is 334. 7 nm, while for x = 10 the value of the absorption edge shifts to the 364.2 nm.
The refractive index (n) for the presented glasses is also established from the optical absorption spectra. It is found that the refractive index increases with the increasing WO3 content indicating the more densely packed structure in the presence of tungsten [26].
Some structural information also can be obtained from the optical band gap values (Eg) evaluated from the UV-Vis spectra with the Tauc method by plotting (F(R∞) hν)n , where n = 0.5 or 2 for direct or indirect transition versus hν (incident photon energy), as shown in Figure 4, a, b and in Table 1 [27]. As it is seen from the Table 1, the Eg values of glasses containing both MoO3 and WO3, increases with the increasing WO3 content due to an increase of the bridging W – O – W bonds concentration as a result of the accumulation of WO6 structural units and their gradual polymerization [28]. This result coincide well with the variation in the physical parameters established. On the other hand Eg value of the molybdate glass x= 0 is lower than that of tungstate glass x = 50 evidencing the higher number of non-bridging oxygen species in the structure of glass x = 0 since it is accepted that in metal oxides, the creation of non-bonding orbitals with higher energy than bonding ones shifts the valence band to higher energy, which results in Eg decreasing [29].
To summarize this section,the Raman data obtained and as well as the established values of the structurally sensitive physical parameters demonstrate that the structure of (50-x) MoO3:xWO3:25La2O5:25B2O3:3Eu3+ (x=0, 10, 20, 30, 40, 50 mol%) glasses consists of mainly (MoO4)2- and (WO4)2- tetrahedral units which fraction changes continuously with the substitution of WO3 for MoO3. BO3, BO4 groups and B-O-B bonds also exist in the glass networks. Also with the replacement of MoO3 with WO3 some amount of WO6 octahedra are produced, which number increases with the increasing WO3 content. The WO6 octahedra gradually polymerase forming W-O-W bonds with the increasing WO3 content. Thus with the substitution of MoO3 with WO3 more disordered and connected glass structure is formed which is favorable for doping with Eu3+ active ions. DTA analysis also shows the increasing values of glass transition temperatures with the increasing WO3 concentration confirming the formation of more connected and stable glass networks.

2.3. Luminescent properties

The photoluminescence excitation (PLE) spectra of the Eu3+ doped glasses are displayed in Figure 5. All data were obtained at room temperature by monitoring the most intensive characteristic emission of Eu3+ ions at 613 nm wavelength, corresponding to 5D0 → 7F2 transition. From Figure 5 it can be observed that the PLE spectra consist of broad continuous band ranging from 220 to 350 nm and narrow - peaks in 350 - 600 nm wavelength range. Generally, the excitation broadband in the ultraviolet region arises due to the ligand - to - metal charge transfer (LMCT) from O2– ligand to W6+/Mo6+ ions in WOn groups (WOn = WO4 and WO6) and MoOn groups (MoOn = MoO4) of the glass matrix as well as from O2– ions to Eu3+ ions, i.e. electron transfer from the 2p orbital of O2– to the empty 4f orbital of Eu3+ [30,31,32,33,34]. As it is seen from the Figure 5, in the PLE spectrum of the glass x = 50, two maxima of the LMCT band are observed – one at about 260 nm and the other at about 325 nm. Considering the previous assignements of PLE peaks of Eu3+ ions [34,35], the bands at around 260 nm and 325 nm in the excitation spectra obtained would be assigned mainly to the O2–→ Eu3+ and O2–→W6+/Mo6+ LMCT transitions, respectively.The stronger intensity of the band at around 260 nm compared to the band at around 325 nm suggests that the O2–→ Eu3+ LMCT is taking place largely in the glass x = 50.
The presence of the excitation band of MoOn and WOn groups, recorded at the emission wavelength of Eu3+ at 613 nm suggests the existence of non - radiative energy transfer from glass matrix to the active rare earth ion [34,36]. As can be seen, the intensity of this band highly depends on the WO3 concentration and increases with the increasing of WO3 content, suggesting that the energy transitions O2– → W6+, in comparison to O2– → Mo6+, largely influence the intensity of the charge transfer absorption band of host matrix. Thus, it can be assumed that WO3 will contribute predominantly to the non - radiative energy transfer to the Eu3+ active ions and the glasses containing significant tungsten oxide concentrations will exhibit the most intense emission. This process is known as host sensitized luminescence.
The excitation spectra also show several peaks between 350 - 600 nm wavelength range, assigned to the f - f intra - configurational forbidden transitions of Eu3+ from the ground state (7F0) and from the first excited state (7F1): 7F0 → 5D4 (363 nm), 7F1 → 5L7 (383 nm), 7F0 → 5L6 (395 nm), 7F0 → 5D3 (412 nm), 7F0 → 5D2 (463 nm), 7F0 → 5D1 (523 nm), 7F1 → 5D1 (531 nm) and 7F0 → 5D0 (577 nm) [37], of which the 7F0 → 5L6 (395 nm) transition is the most intensive and was considered as an excitation wavelength to record the emission spectra. Compared to the LMCT, the f - f transitions are stronger and their intensity increases, as the concentration of WO3 increases, which is advantageous for achieving appropriate excitation by near - UV and blue LED chips, since in general the intensity of these Eu3+ transitions is weak due to the fact that they are forbidden by the Laporte`s selection rule [38].
The photoluminescence emission (PL) spectra of Eu3+ - doped glasses, recorded under the most intensive Eu3+ excitation at 395 nm light are shown in Figure 6. The characteristic emission peaks originated from the radiative transitions of Eu3+ ions from the 5D0 excited state to the lower - lying 7F0, 7F1, 7F2, 7F3, 7F4 ground states are observed at 580 nm, 593 nm, 613 nm, 652 nm and 702 nm, respectively. The dominant luminescent band is located at 613 nm. From Figure 6 it is clear that the emission intensity strongly depends on the WO3 concentration and increases considerably as its content increases. This observation may be due to the occurring non-radiative charge transfer from glass host to the active Eu3+ ion. Evidence for the existence of the energy transfer is the absence of the characteristic broad emissions of WO3 and MoO3 in the spectral range 400 - 600 nm [39,40] arising from the fact that the energy absorbed by the tungstate and molybdate groups has transferred non - radiatively to the active Eu3+ ion.
Among all the observed emission transitions, 5D0→7F2 transition is identified as electric dipole (ED) and is forced by the crystal field environment in the vicinity of the Eu3+ ions, while 5D0→7F1 transition is allowed magnetic dipole (MD) in nature, independent of host matrix.
When Eu3+ ions are embedded in sites with inversion symmetry, the 5D0→7F1 magnetic dipole transition will dominate; on the contrary, when a Eu3+ ion site is noncentrosymmetric, the 5D0→7F2 electric dipole transitions will be the strongest in the emission. As a result, the luminescence intensity ratio (R) between electric (5D0→7F2) and magnetic (5D0→7F1) dipole transitions can be used as a probe to the nature of the site and symmetry of the coordination sphere and provide valuable information about the local symmetry around the rare earth ion, the strength of covalent bonding between Eu3+ and its surrounding ligands and the emission intensity. The higher the value of R, the more distortion from inversion symmetry is observed, as well as higher covalency between Eu3+ and O2– ions and increased emission intensity [37,41,42]. The calculated intensity ratios R (7.09-7.82) of the obtained glasses (Table 2) are higher than those of previously synthesized by us glasses [20,43,44,45,46] and than other Eu3+ doped oxide glasses reported in literature [47,48,49,50,51,52,53], as well as the commercially available red phosphors Eu3+:Y2O3 [54,55] and Eu3+:Y2O2S [56] suggesting that the synthesized samples are characterized with more asymmetry in the vicinity of Eu3+ ions, stronger Eu - O covalence, and an enhanced emission intensity. From Table 2 it also could be seen that, the value of asymmetric ratio is increasing as the WO3 content increases and as a result stronger luminescence is observed.
Additional evidence of the low site symmetry in the vicinity around the active Eu3+ ions is the presence of the 5D0 → 7F0 transition, which is strictly forbidden and according by Binnemans, appears in emission spectra when Eu3+ ions are located in sites with C2v, Cn or Cs symmetry [37]. To further examine the symmetry of the Eu3+ sites, the 5D0 → 7F1 transition is considered, which displays splittings. This implies that the symmetry of the Eu3+ sites in the studied glasses are C2v or lower [57].
The observed optical properties are discussed on the basis of the glass structural features. The most intensive Eu3+ emission peak, corresponding to the hypersensitive 5D0 → 7F2 transition, along with the high values of the luminescent ratio R, evidence that Eu3+ ions are located in low site symmetry in the host matrix. This emission peak intensity and the R values of investigated glasses increases with the increasing WO3 concentration indicating that the substitution of MoO3 with WO3 contributes to the creation of a more distorted and rigid glass structure that lowers the site symmetry of the rare-earth ion and improves its photoluminescence behavior. Furthemore, the increasing intensity of the band at 613 nm (5D0 → 7F2 transition) with increasing WO3 concentration indicates that the WO3 contributes predominantly to the non - radiative energy transfer to the Eu3+ active ions (host sensitized luminescence). Thus, WO3 is more appropriate component than MoO3 for enhancing the luminescent intensity of the doped Eu3+ ion.

3. Materials and Methods

The glasses with the nominal compositions of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+ , x=10, 20, 30, 40, 50 (mol%) were prepared using a conventional melt quenching method. Reagent grade commercial powders of MoO3, WO3, La2O3, and H3BO3, were used as starting materials and were mixed in an alumina mortar. The batches (each batch weight:10 g) were melted at 1200-1250°C for 30 min in a platinum crucible in air. The glasses were obtained by pouring the melts onto an iron plate and by pressing with another iron plate (cooling rate ~ 10 K/s). The glass transition (Tg) and crystallization peak (Tc) temperatures were determined using differential thermal analysis (DTA) (Rigaki Thermo Plus TG 8120) at heating rate of 10 K/min (±1). Optical absorption spectra at room temperature of glasses were measured in the wavelength range of 200-800 nm using a spectrometer (Shimadzu U-3120). The uncertainty in the observed wavelength is about ±1 nm. Refractive indices at a wavelength (λ) of 632.8 nm (He–Ne laser) were measured at room temperature with a prism coupler (Metricon Model 2010). Densities of the glasses at room temperature were determined with the Archimedes method using distilled water as an immersion liquid in which measurements were repeated five times and the average value was used (±0.001g/cm3). Raman scattering spectra at room temperature were measuresd with a laser microscope (Tokyi Instruments Co. Nanofinder) operated at Ar+ (λ = 448 nm) laser with resolution of ±1 cm-1. PL spectra at room temperature for the glass samples were measured with a PL spectrometer (JASCO FP-6500).

4. Conclusions

The glasses with nominal composition of (50-x)MoO3:xWO3:25La2O3:25B2O3 :3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) were synthesized by melt quenching method and their structure, thermal behavior and luminescent properties were studied. The glass transition temperature increases with the substitution of MoO3 with WO3. Glasses containing higher amount of MoO3 and lower WO3 content up to 20 mol% have the highest thermal stability (ΔT = 145°C for glass x = 10 and ΔT =137°C for glass x= 20). On the base of Raman analysis and as well as density measurements and values of the structurally sensitive physical parameters it was established that the glass structure is build up mainly from (MoO4)2- and (WO4)2- tetrahedral units. WO6 octahedral groups and W-O-W bonds are also formed in the WO3-containing glasses, increasing in number with an increase of WO3 content. The luminescent properties of the obtained Eu3+ - doped glasses revealed that they could be excited by 395 nm and exhibit pure red emission centered at 613 nm (5D0 → 7F2 transition). The Eu3+ luminescent intensity were found to increase with the WO3 loading. All findings obtained here are favorable for the elaboration of novel red-emitting glass materials.

Author Contributions

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

Funding

This research received no external funding.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. DTA curves of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses.
Figure 1. DTA curves of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses.
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Figure 2. Raman spectra of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses.
Figure 2. Raman spectra of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses.
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Figure 3. Optical absorption spectra at room temperature of (50-x)MoO3:xWO3:25La2O3:25B2O3-3Eu3+, x= 0, 10,20, 30, 40, 50 mol% glasses.
Figure 3. Optical absorption spectra at room temperature of (50-x)MoO3:xWO3:25La2O3:25B2O3-3Eu3+, x= 0, 10,20, 30, 40, 50 mol% glasses.
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Figure 4. Tauc plot of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses: a) for direct transition, b) for indirect transition.
Figure 4. Tauc plot of (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x= 0, 10, 20, 30, 40, 50 mol% glasses: a) for direct transition, b) for indirect transition.
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Figure 5. Excitation spectra of (50–x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) glasses.
Figure 5. Excitation spectra of (50–x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) glasses.
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Figure 6. Emission spectra of (50–x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) glasses.
Figure 6. Emission spectra of (50–x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) glasses.
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Table 1. Values of physical parameters of glasses (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x=10, 20, 30, 40, 50 mol%: density (ρg), molar volume (Vm), oxygen molar volume (Vo), oxygen packing density (OPD), Optical band gap (Eg), absorption edge A, refractive index, n.
Table 1. Values of physical parameters of glasses (50-x)MoO3:xWO3:25La2O3:25B2O3:3Eu3+, x=10, 20, 30, 40, 50 mol%: density (ρg), molar volume (Vm), oxygen molar volume (Vo), oxygen packing density (OPD), Optical band gap (Eg), absorption edge A, refractive index, n.
Sample
ID		 ρg (±0.01)
(g/cm3)		 Vm
(cm3/mol)		 Vo
(cm3/mol)		 OPD
(g atom/l)		 Eg direct
(eV)		 Eg indirect
(eV)		 А
(nm)		 Refractive index, n
x = 0 4.756 38.14 12.34 81.02 3.50 3.31 350.7 1.93144
x = 10 4.992 38.10 12.33 81.10 3.37 3.12 367.2 1.93452
x = 20 5.439 36.58 11.84 84.47 3.39 3.16 364.1 1.94278
x = 30 5.729 36.26 11.73 85.22 3.43 3.19 359.8 1.95236
x = 40 6.064 35.71 11.56 86.53 3.46 3.27 353.7 1.96115
x = 50 6.403 35.19 11.39 87.81 3.66 3.50 334.7 1.97066
Table 2. Relative luminescent intensity ratio (R) of the two transitions (5D0 → 7F2 )/(5D0 → 7F1 ) for (50-x)MoO3:xWO3:25La2O3:25B2O3 :3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) glasses.
Table 2. Relative luminescent intensity ratio (R) of the two transitions (5D0 → 7F2 )/(5D0 → 7F1 ) for (50-x)MoO3:xWO3:25La2O3:25B2O3 :3Eu3+ (x = 0, 10, 20, 30, 40 and 50 mol%) glasses.
Glass composition Relative Intensity Ratio, R reference
50MoO3:25La2O3:25B2O3:3Eu2O3 7.09 Current work
40MoO3:10WO3:25La2O3:25B2O3:3Eu2O3 7.15 Current work
30MoO3:20WO3:25La2O3:25B2O3:3Eu2O3 7.19 Current work
20MoO3:30WO3:25La2O3:25B2O3:3Eu2O3 7.42 Current work
10MoO3:40WO3:25La2O3:25B2O3:3Eu2O3 7.63 Current work
50WO3:25La2O3:25B2O3:3Eu2O3 7.82 Current work
50ZnO:40B2O3:10WO3:xEu2O3 (0≤x≤10) 4.54÷5.77 20
50ZnO:40B2O3:5WO3:5Nb2O5:xEu2O3 (0≤x≤10) 5.09÷5.76 43
50ZnO:(50–x)B2O3:xNb2O5:0.5Eu2O3:, x= 0, 1, 3 and 5 mol% 4.31-5.16 44
50ZnO:(50−x)B2O3:0.5Eu2O3:xWO3, x = 0, 1, 3, 5. 4.34-5.57 45
50ZnO:(49–x)B2O3:1Bi2O3:xWO3; x = 1, 5, 10, 4.61-5.73 46
4ZnO:3B2O3 0.5–2.5 mol % Eu2O3 2.74-3.94 47
60ZnO:20B2O3:(20 − x)SiO2−xEu2O3 (x = 0 and 1) 3.166 48
15PbF2:25WO3:(60–x)TeO2:xEu2O3 x = 0.1, 0.5, 1.0 and 2.0 mol% 2.37-2.78 49
20PbO–5CaO–5ZnO–10LiF–59B2O3–1Eu2O 2.320 50
45SiO2−(20−x)PbF2−20K2O−5Na2O−10LiF−1.0Eu2O3 2.44 51
89.5B2O3–10Li2O–0.5Eu2O3 2.41 52
57GeO2–40K2O–3Eu2O3 3.70 52
73P2O5–25CaO–2Eu2O3 3.95 52
79TeO2−20Li2CO3−1Eu2O3 4.28 53
Eu3+:Y2O3 3.8-5.2 54, 55
Eu3+:Y2O2S 6.45-6.62 56
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