Judd–Ofelt Analysis and Spectroscopy Study of Tellurite Glasses Doped with Rare-Earth (Nd3+, Sm3+, Dy3+, and Er3+)

A series of glasses based on (80-y) TeO2-20 BiCl3-y RE2O3 (y = 0, 0.6 mol%; RE = Nd, Sm, Dy, and Er) were prepared. The thermal stability of the glass was determined by differential scanning calorimetry (DSC). The density and optical energy values of the prepared glass increased in the order of Sm2O3, Nd2O3, Dy2O3, and Er2O3. In addition, the glass doped with Er2O3 had the highest refractive index values compared to the other samples. Subsequently, Judd–Ofelt parameters (Ω2, Ω4, and Ω6) were obtained for the family of RE3+ trivalent rare-earth ions introduced as dopants in a tellurite glass. These parameters were calculated from the absorption spectra for each RE3+. The structures were studied by Raman spectroscopy deconvolution, which determined that TeO4, TeO3, TeO3+1, BiO6, and BiCl6 units had formed. In addition, the structural changes in the glass are related to the intensity ratio of TeO4/TeO3, depending on the type of rare-earth. For the optics and Judd–Ofelt parameters, the ray spectroscopy results of the prepared glass show that it is a good candidate for nonlinear optics fibers, a solid laser material.


Introduction
Nd, Sm, Dy, and Er are examples of rare-earth (RE) elements that have several multilateral uses in innovative technology [1].Due to the fact that it is utilized to make optoelectronic components, including planar waveguides, optical detectors, fluorescent display technology, visible lasers, optical fibers, and optical amplifiers, rare-earth (RE) ion-doped glass has recently attracted interest [2].
Tellurite oxide-based glasses offer special physical characteristics features such as high linear and nonlinear indices of refraction, low melting points, simple forming and dimensions, high transparency, chemical resistance, high thermal stability, and infrared transmittance [3].Glasses including TeO 2 have potential applications in the fields of photonics; optoelectronics; and optical instrumentation, including laser technology, telecommunications, amplifiers, and electrical storage devices [4].
Additionally, tellurium dioxide is convertible with other glass materials, enabling the incorporation of several compositions inside tellurate glass.These glasses are thought to be effective hosts, enhancing the luminescence characteristics of a number of lanthanide ions.Therefore, it is interesting to peer into the tellurate glass's structure, particularly when the glass is doped with rare-earth ions.An asymmetrical TeO 4 trigonalbipyramidal (tbp), which contains two axials, two different kinds of sites, and three equatorial positions, is the distinctive structural unit of crystalline TeO 2 .An individual pair of electrons is present in one of the latter.There are two distinct types of fundamental structural units in TeO 2 -based glasses, namely TeO 4 tbp and TeO 4 tbp with a lone pair electron, which makes their structure interesting.
The addition of bismuth chloride (BiCl 3 ) as a second glass forming helps in the creation of superior structural units, which have an impact on the physical and optical characteristics of the glass system.Tellurite glass research has attracted a lot of attention.Due to its potential applications in various industries, this has changed recently.Doped with appropriate rare-earth (RE) ions, tellurite glass is a candidate for use in optical fibers, nonlinear optics, lasers, solar cells, and sensors [5].Sm 2 O 3 -doped glass exhibits and produces an intense orange-red luminescence in the visible region related to the 4 G 5/2 and 6 H 9/2 transitions, depending on the excitation wavelength.Glass that has Er 2 O 3 is thought to be a potential material for optical amplifier production (EDFAS) and the application of optical communications.
The J-O intensity characteristics also reveal the glass bonding type, according to a number of scientists, in order to know more about the optical and physical characteristics of Nd 3+ , Sm 3+ , Dy 3+ , and Er 3+ ions in the glass matrix, as well as the radiative lifetimes of erbium doped in tellurite glasses.Research has also looked into determining the feasibility of applying this glass system in optical glasses for photonics and lasers.
A reliable approach for determining estimated radiative properties such as the rate of spontaneous emission, duration, and branching ratio is the Judd-Ofelt analysis.Furthermore, the computation of the gain and quantum efficiency includes a few Judd-Ofelt spectroscopic parameters [6,7].When choosing a vitreous matrix, several glasses' chemical compositions have been adjusted.Low phonon energy considerably increases the probabilities of radiative transition in glasses such as fluoro-zirconate and heavy metal oxide-based glasses (HMOGs), making these glasses the best candidates for photoluminescence [8].
The current work uses the Judd-Ofelt method to investigate the radiative characteristics of tellurate glasses (TeO 2 -BiCl 3 ) doped with lanthanide ions (Nd 3+ , Sm 3+ , Dy 3+ , and Er 3+ ).In order to investigate whether these rare-earth ions influence the structural characteristics of the TB glass system, we provide general physical and optical characteristics.The structure of these glasses has been extensively studied using the Raman technique.

Glass Synthesis
With a chemical formula of (80-y) TeO 2 -20 BiCl 3 -y RE 2 O 3 (y = 0, 0.6% mol; RE = Nd, Sm, Dy, and Er), glass samples from Sigma Aldrich (St. Louis, MO, USA) were created with a high purity of 99.9%.To remove adsorbed water, all chemical compositions were preheated in a furnace at 200 • C for 3 h.The glass sample code and material composition are shown in Table 1.Each of the components was weighed and combined in a mortar using a weight (about 5 g), and the mixtures were melted at a temperature of 750 • C in the air under flame heat for 10 min until a homogeneous liquid was obtained.Then, the melt was cast on a mold brass, maintained at a temperature lower than the glass transition (T ≈ T g − 10 • C).The obtained glasses were annealed for 6 h at T g -20 • C in an electric furnace to eliminate the stresses induced during quenching.The photography of the samples is presented in the Figure 1.The samples were polished and cut to a few millimeters thick.The current study investigates the radiative properties of tellurate glasses (TeO 2 -BiCl 3 ) doped with lanthanide ions (Nd 3+ , Sm 3+ , Dy 3+ , and Er 3+ ) using the Judd-Ofelt method.We present general physical and optical features to evaluate whether these rareearth ions affect the structural properties of the TB glass system.The Raman method has been used for considerable research on the structure of these glasses.method.We present general physical and optical features to evaluate whether these ra re-earth ions affect the structural properties of the TB glass system.The Raman method has been used for considerable research on the structure of these glasses.

Characterization
By utilizing CuKα radiation at 40 kV and 100 mA during XRD studies SHIMADZU XRD 6000 (Chiyoda-ku, Tokyo, Japan) the materials' amorphous natures are confirmed The 2θ range had a step size of 0.04° per second and a range of 0-60°.Glass density measurements were taken with a precision of 0.001 g/cm 3 utilizing the Archimede method.The TA Instrument DSC Q20 model (New Castle, DE, USA) which has a greate sensitivity of 0.1 °C and a heating rate of 10 K/min, was used to record the samples thermal properties.The Tg value was judged to be 2 K, whereas the Tx and Tp value were 1 K.The Tx-Tg stability factor demonstrated the outstanding stability of our glasses A Scienta Omicron R3000 spectrometer (Danmarksgatan 22, Uppsala, Sweden) oper ating between 100 and 1000 cm −1 was used for the Raman spectroscopy.Measurements o the optical transmissions in the UV-Visible band between 400 and 800 nm were per formed using an Agilent Technologies Cary 5000 spectrometer (Santa Clara, CA,USA) .

X-ray Diffraction Analysis
The X-ray diffraction patterns of a system glass made of (80-y) TeO2-20 BiCl3-y RE2O (y = 0, 0.6% mol; RE = Nd, Sm, Dy, and Er) are depicted in Figure 2. A broad peak curve was seen between 20° and 30° of the 2θ.The absence of diffraction peaks confirms the amorphous structure of these glasses [9].

Characterization
By utilizing CuKα radiation at 40 kV and 100 mA during XRD studies SHIMADZU XRD 6000 (Chiyoda-ku, Tokyo, Japan) the materials' amorphous natures are confirmed.The 2θ range had a step size of 0.04 • per second and a range of 0-60 • .Glass density measurements were taken with a precision of 0.001 g/cm 3 utilizing the Archimedes method.The TA Instrument DSC Q20 model (New Castle, DE, USA) which has a greater sensitivity of 0.1 • C and a heating rate of 10 K/min, was used to record the samples' thermal properties.The Tg value was judged to be 2 K, whereas the Tx and Tp values were 1 K.The Tx-Tg stability factor demonstrated the outstanding stability of our glasses.A Scienta Omicron R3000 spectrometer (Danmarksgatan 22, Uppsala, Sweden) operating between 100 and 1000 cm −1 was used for the Raman spectroscopy.Measurements of the optical transmissions in the UV-Visible band between 400 and 800 nm were performed using an Agilent Technologies Cary 5000 spectrometer (Santa Clara, CA, USA).

X-ray Diffraction Analysis
The X-ray diffraction patterns of a system glass made of (80-y) TeO 2 -20 BiCl 3 -y RE 2 O 3 (y = 0, 0.6% mol; RE = Nd, Sm, Dy, and Er) are depicted in Figure 2. A broad peak curve was seen between 20 • and 30 • of the 2θ.The absence of diffraction peaks confirms the amorphous structure of these glasses [9].

Thermal Properties
Figure 3 displays the differential scanning calorimetry (DSC) patterns for each of the investigated glass samples: the glass transition temperature (Tg), the onset crystallization peak temperature (Tx), the peak of the crystallization temperature (Tp), the thermal sta-

Thermal Properties
Figure 3 displays the differential scanning calorimetry (DSC) patterns for each of the investigated glass samples: the glass transition temperature (T g ), the onset crystallization peak temperature (T x ), the peak of the crystallization temperature (T p ), the thermal stability factor ∆T = T x -T g [10], and Hruby's parameter H = (T x -T g )/T g .

Thermal Properties
Figure 3 displays the differential scanning calorimetry (DSC) patterns for each of investigated glass samples: the glass transition temperature (Tg), the onset crystallizat peak temperature (Tx), the peak of the crystallization temperature (Tp), the thermal bility factor ΔT = Tx -Tg [10], and Hruby's parameter H= (Tx -Tg)/ Tg .Table 2 lists the glasses' thermal stability of anticrystallization or resistance to cr tallization [11].The Tg, Tx, Tp, ΔT, H, and S are in the range of 285-333 °C, 390-439 430-477 °C, 116-127 °C, 0.32-0.44,and 7.54-15.63°C, respectively, according to Tabl The rigidity of the network is what causes an increase in the Tg with the addition of mol% of Nd2O3, Sm2O3, Dy2O3, and Er2O3 in the glass system.Glass is considered th mally stable if the difference ∆T, which is used to calculate thermal stability, is larger t 100 °C.The ΔT was greater than 100 °C for all glass samples.TB4 had the highest g stability (127 °C) [12].
Glass stability can be shown by Hruby's parameters; a greater H denotes an proved degree of glass formation stability.The highest value of H is displayed by T glass, with a value of 0.44 signifying the highest glass-forming potential.Because ther a significant correlation between the stability of the glass and exothermic broadness, thermal stability, S, given by Saad and Bolin, stands out [13].The resistance is reflected the parameter S. The value at TB2 was the greatest, and the value at TB4 was the low The alteration in solid-state bond formation in complex matrices is related to change the material's thermal characteristics.Table 2 lists the glasses' thermal stability of anticrystallization or resistance to crystallization [11].The T g , T x , T p , ∆T, H, and S are in the range of 285-333 • C, 390-439 • C, 430-477 • C, 116-127 • C, 0.32-0.44,and 7.54-15.63• C, respectively, according to Table 2.The rigidity of the network is what causes an increase in the Tg with the addition of 0.6 mol% of Nd 2 O 3 , Sm 2 O 3 , Dy 2 O 3 , and Er 2 O 3 in the glass system.Glass is considered thermally stable if the difference ∆T, which is used to calculate thermal stability, is larger than 100 • C. The ∆T was greater than 100 • C for all glass samples.TB4 had the highest glass stability (127 • C) [12].
Table 2.The glass transition temperature T g , onset crystallization temperatures T x , crystallization temperatures T p , thermal stability factor ∆T, Hruby parameter, and glass stability range S of the (80-y) TeO 2 -20 BiCl 3 -y RE 2 O 3 (y = 0, 0.6% mol; RE = Nd, Sm, Dy, and Er) glass system.Glass stability can be shown by Hruby's parameters; a greater H denotes an improved degree of glass formation stability.The highest value of H is displayed by TB4 glass, with a value of 0.44 signifying the highest glass-forming potential.Because there is a significant correlation between the stability of the glass and exothermic broadness, the thermal stability, S, given by Saad and Bolin, stands out [13].The resistance is reflected in the parameter S. The value at TB2 was the greatest, and the value at TB4 was the lowest.The alteration in solid-state bond formation in complex matrices is related to changes in the material's thermal characteristics.
where u a and u b are the weights of the glass sample in air and in immersion liquid, respectively, and ρ wat is the water density.The calculated density value of the prepared glass decreased from 5.506 g/cm 3 to 5.468 g/cm 3 , which corresponded to TB and TB4 glass.Table 3 presents the results.Rare-earth compounds are ranked according to their molecular weights (M wt ) as follows: TB1 < TB2 < TB3 < TB4, with respective M wt values of 191.879, 191.953, 192.098, and 192.156 g/mol.Erbium-doped glass is denser and more compact than undoped glass.Using Equations ( 2) and ( 3), find out how much glass there is in the sample and how much oxygen there is in the sample.Table 2 lists the density of the glass samples used to carry out these calculations.
where M i is the molecular weight, and X i is the fraction ratio of every oxide.The oxygen molar volume, V OXG , can be calculated using the relationship below.
where n i is the number of individual oxide oxygen atoms [11].From 35.10 cm 3 /molto 35.01 cm 3 /mol, corresponding to TB1 and TB4, the molar volume, V mol , decreased.From 45.86 cm 3 /mol, V O decreased to 45.74 cm 3 /mol.In addition, it is possible that the reduction in V O reflected an increase in the synthesis of NBO atoms, given that the OPD was determined using Equation ( 4) [2].
The value of OPD reduced from 21.87 to 21.65 g atom/l as the rare-earth ions in the glass matrix were doped.
The polaron radius r pl (A • ), inter ionic distance r in (A • ), and field strength Fs (×10 17 cm −2 ) were calculated from Equations ( 5)-( 8) [15].The concentration of ions: where (N RE ) is the concentration of rare-earth ions, (N AVG ) is the Avogadro's number, (ρ g ) is the density of the glass sample, A is the atomic mass of the rare-earth ions, (r in ) is the mean distance between the RE 3+ ions, (r pl ) is the polaron radius, and (F s ) is the field strength of TB glass that has been doped.Table 3 displays the results of the calculations.The estimated results show that, for RE +3 ions, ri and rp are identical.As a result, the field strength (F) surrounding Er +3 ions is enhanced, and the RE-O bond becomes more stable.When taken together with the intensity results, these values prove that the addition of Er 3+ ions causes the glass structure to compress, which, in turn, reduces the degree of electron delocalization by increasing the number of donor centers in the glass matrix, which reduces the optical band gap [9].Using Davis's and Mott's relation and Equation (9), the Eopt for amorphous material was calculated [16]. (αhυ For every value of r between 1/2 and 2, where B is a constant, allowable indirect transitions have an r value of 1/2, whereas direct transitions have an r value of 2 in Equation (10).The values of indirect Eopt were calculated by extrapolating the linear fit on the x-axis of the plot of (αhν) 1/2 against photon hν, as shown in Figure 4. ( ) ( ) The Eopt value ranges from 2.75 to 2.99 eV, depending on the kind of glass and it was manufactured.Table 3 displays   With the change in the doping RE 3+ ion concentration in the produced glass, value rises from 2.39 to 2.47.The molar mass, electron density, and ion polarity a factors.Strong polarization of non-bridged oxygen production (NBO) in the glass is responsible for the enhancement of the refractive index.The polarizability is incr due to the greater refractive index resulting from the creation of non-bridging o when compared to covalent oxygen bridging bonds.
The calculation of the molar refraction (Rmol, cm 3 /mol) is carried out by usin Lorentz-Lorenz Equation ( 12) [11]:  ( ) ( ) The Eopt value ranges from 2.75 to 2.99 eV, depending on the kind of glass and how it was manufactured.Table 3 displays the values of Eopt for each sample, with TB having the highest value and TB4 the lowest.
The index of refraction n is one of the most important characteristics of optical glasses.The refractive index values of prepared glass samples were obtained using the Dimitrov and Sakka relation, as depicted in Equation (11) [17] and tabulated in Table 3.
With the change in the doping RE 3+ ion concentration in the produced glass, the n value rises from 2.39 to 2.47.The molar mass, electron density, and ion polarity are all factors.Strong polarization of non-bridged oxygen production (NBO) in the glass lattice is responsible for the enhancement of the refractive index.The polarizability is increased due to the greater refractive index resulting from the creation of non-bridging oxygen when compared to covalent oxygen bridging bonds.
The calculation of the molar refraction (Rmol, cm 3 /mol) is carried out by using the Lorentz-Lorenz Equation ( 12) [11]: The calculation of the molar polarizability (αmol) can be determined using Equation The Eopt value ranges from 2.75 to 2.99 eV, depending on the kind of glass and how it was manufactured.Table 3 displays the values of E opt for each sample, with TB having the highest value and TB4 the lowest.
The index of refraction n is one of the most important characteristics of optical glasses.The refractive index values of prepared glass samples were obtained using the Dimitrov and Sakka relation, as depicted in Equation (11) [17] and tabulated in Table 3.
With the change in the doping RE 3+ ion concentration in the produced glass, the n value rises from 2.39 to 2.47.The molar mass, electron density, and ion polarity are all factors.Strong polarization of non-bridged oxygen production (NBO) in the glass lattice is responsible for the enhancement of the refractive index.The polarizability is increased due to the greater refractive index resulting from the creation of non-bridging oxygen when compared to covalent oxygen bridging bonds.
The calculation of the molar refraction (R mol , cm 3 /mol) is carried out by using the Lorentz-Lorenz Equation ( 12) [11]: The calculation of the molar polarizability (α mol ) can be determined using Equation ( 13): Table 3 presents the values of polarizability (α mol ) and molar refraction (R mol ) for the glass samples doped with rare-earth ions.The dielectric constant (ε) and refraction loss (R L ) are determined using Equations ( 14) and (15), respectively [11].
The increase in the R mol , α mol , ε, and R Loss can be attributed to an increase in the (NBO) and RE 3+ ions in the glasses' network structure.

Judd-Ofelt Analysis
Laser action and optical amplification are two phenomena for which the J-O theory is often utilized to make predictions.Bands of absorption were seen in this research, and it was shown that they were most often connected with transitions involving induced electric dipoles [7,18].Oscillator strength was defined as the intensity of the absorption spectral lines.Furthermore, Equation ( 16) [8,14] was utilized to calculate the experimental oscillator strength ( f exp ) for each absorption band.
where ε(υ) = 1 Ck • log I 0 I represents the molar extinction coefficient in cm −1 , k represents the optical path length in cm, C represents the concentration of RE 3+ in mol.L −1 , and ε(υ)dυ represents the area under the absorption curve.The transition frequency ( f cal ) between RE 3+ 's ground state (aJ) and excited state (aJ') was calculated.Equation (17) was used to determine the ionization transition.
The variables X ed and X md represent Lorentz-localized field corrections that are accountable for the dipole transitions, and h is the Planck's constant.They are written using the refractive index n as n is the glass sample's determined refractive index.The line strength for both electric and magnetic dipoles, S ed and S md , respectively, can be calculated as follows.
S ed aj, aj = e 2 ∑ λ=2,4,6 Ω λ aj 2 (20) The values of the doubly reduced matrix elements of order Ω λ (λ = 2, 4, 6) between the manifold states of | aj | 2 and | aJ | 2 were obtained from [14,19].The J-O intensity parameters were calculated using the least squares fitting method.The root mean square (RMS) deviation was used to assess the quality of fitting between f cal and f exp .
ε represents the total number of observed transitions.The probability of spontaneous transition A(aJ, bJ ) is given by The average magnetic and electric dipole contributions are denoted by A md and A ed , respectively.Expression (24) yields the branching ratio (β R ) for the upper state J.
The radiative lifetime (τ) of the emitting state is related to the global spontaneous probabilities A(aJ, bJ ) [19] for the overall transitions.
The upper state's total angular momentum is denoted by J.

Spectra of Absorption and Judd-Ofelt Analysis
We provide data for the full RE 3+ series, including experimental and calculated oscillator strength for the corresponding transitions, absorption spectra, J-O parameters, and root mean square (RMSE) error of the oscillator strength calculations.

Neodymium (Nd 3+ )
From 350 to 1200 nm, Figure 5 displays the absorption bands that were produced when Nd 3+ ions were doped into glass.The spectral lines from the lowest level, 4 I 9/2 , to the highest, the excited levels, are clearly visible.Table 4 [20].The experimental and calculated oscillator strengths for the Nd 3+ ions agreed with the J-O calculations for the most part, but there were some challenges in determining the oscillator strength in the UV region due to the overlapping bands of the following transitions: 4 I 9/2 ( 2 P 1/2 ), ( 2 K 15/2 , 2 G 9/2 , 2 D 3/2 , 2 G 11/2 ), and ( 2 K 13/2 , 4 G 7/2 , 4 G 9/2 ).Other authors have suggested that the most effective transition is the hypersensitive 4 ).These findings follow the same quadrupole selection rules ( |∆S| ≤ 0, |∆L|, |∆J| ≤ 2) as those found in bismuth borated glasses and other fluorophosphate glasses [21,22].Visible range absorption spectra were assigned, as seen in Figure 6.Considerin intricacy of the total of the 2S+1 LJ transitions, it was not surprising that calculating th parameters was complex.The oscillator strengths at the ground level 6 H5/2 and the ex levels 6 H13/2, 6 F1/2 + 6 H15/2, 6 F3/2, 6 F5/2, 6 F7/2, 6 F9/2, and 6 F11/2 were measured experimentall computed [23].As shown in Table 5, there was a high agreement between the ex mental and calculated oscillator strengths and the J-O parameters, proving the acc of the J-O predictions.Consistent with previous research by authors such R. Van De al. [18], the findings show that the strongest transitions occur in the near-infrared spectrum between 950 nm and 1600 nm.

Samarium (Sm 3+ )
Visible range absorption spectra were assigned, as seen in Figure 6.Considering the intricacy of the total of the 2S+1 LJ transitions, it was not surprising that calculating the J-O parameters was complex.The oscillator strengths at the ground level 6 H5/2 and the excited levels 6 H13/2, 6 F1/2 + 6 H15/2, 6 F3/2, 6 F5/2, 6 F7/2, 6 F9/2, and 6 F11/2 were measured experimentally and computed [23].As shown in Table 5, there was a high agreement between the experimental and calculated oscillator strengths and the J-O parameters, proving the accuracy of the J-O predictions.Consistent with previous research by authors such R. Van Deun et al. [18], the findings show that the strongest transitions occur in the near-infrared (NIR) spectrum between 950 nm and 1600 nm.Visible range absorption spectra were assigned, as seen in Figure 6.Considering the intricacy of the total of the 2S+1 L J transitions, it was not surprising that calculating the J-O parameters was complex.The oscillator strengths at the ground level 6 H 5/2 and the excited levels 6 H 13/2 , 6 F 1/2 + 6 H 15/2 , 6 F 3/2 , 6 F 5/2 , 6 F 7/2 , 6 F 9/2 , and 6 F 11/2 were measured experimentally and computed [23].As shown in Table 5, there was a high agreement between the experimental and calculated oscillator strengths and the J-O parameters, proving the accuracy of the J-O predictions.Consistent with previous research by authors such R. Van Deun et al. [18], the findings show that the strongest transitions occur in the near-infrared (NIR) spectrum between 950 nm and 1600 nm.
computed [23].As shown in Table 5, there was a high agreement between the ex mental and calculated oscillator strengths and the J-O parameters, proving the accu of the J-O predictions.Consistent with previous research by authors such R. Van De al. [18], the findings show that the strongest transitions occur in the near-infrared ( spectrum between 950 nm and 1600 nm.Visible range absorption spectra were assigned, as seen in Figure 6.Considering the intricacy of the total of the 2S+1 LJ transitions, it was not surprising that calculating the J-O parameters was complex.The oscillator strengths at the ground level 6 H5/2 and the excited levels 6 H13/2, 6 F1/2 + 6 H15/2, 6 F3/2, 6 F5/2, 6 F7/2, 6 F9/2, and 6 F11/2 were measured experimentally and computed [23].As shown in Table 5, there was a high agreement between the experimental and calculated oscillator strengths and the J-O parameters, proving the accuracy of the J-O predictions.Consistent with previous research by authors such R. Van Deun et al. [18], the findings show that the strongest transitions occur in the near-infrared (NIR) spectrum between 950 nm and 1600 nm.In Figure 7, we see the spectra of TB3 glass, which has many bands concentrated in the 700 to 1900 nm range.The transition from the ground state 6 H 15/2 to the excited states 6 H 11/2 , 6 F 11/2 + 6 H 9/2 , 6 F 9/2 + 6 H 7/2 , 6 F 7/2 + 6 H 5/2 , 6 F 5/2 , and 6 F 3/2 + 6 F 1/2 , respectively, is reflected in absorption bands at 1686, 1279, 1095, 903,803, and 753 nm for Dy 3+ with the 4f 9 electronic configuration [24].Table 6 shows the calculated and experimental oscillator strengths, as well as the J-O parameters.In Figure 7, we see the spectra of TB3 glass, which has many bands concentrate the 700 to 1900 nm range.The transition from the ground state 6 H15/2 to the excited s 6 H11/2, 6 F11/2 + 6 H9/2, 6 F9/2 + 6 H7/2, 6 F7/2 + 6 H5/2, 6 F5/2, and 6 F3/2 + 6 F1/2, respectively, is reflect absorption bands at 1686, 1279, 1095, 903,803, and 753 nm for Dy 3+ with the 4f 9 electr configuration [24].Table 6 shows the calculated and experimental oscillator strength well as the J-O parameters.Visible range absorption spectra were assigned, as seen in Figure 6.Considering the intricacy of the total of the 2S+1 LJ transitions, it was not surprising that calculating the J-O parameters was complex.The oscillator strengths at the ground level 6 H5/2 and the excited levels 6 H13/2, 6 F1/2 + 6 H15/2, 6 F3/2, 6 F5/2, 6 F7/2, 6 F9/2, and 6 F11/2 were measured experimentally and computed [23].As shown in Table 5, there was a high agreement between the experimental and calculated oscillator strengths and the J-O parameters, proving the accuracy of the J-O predictions.Consistent with previous research by authors such R. Van Deun et al. [18], the findings show that the strongest transitions occur in the near-infrared (NIR) spectrum between 950 nm and 1600 nm.Starting with the ground state 4 I 15/2 to the excited states 4 I 13/2 , 4 I 11/2 , 4 I 9/2 , 4 F 9/2 , 4 S 3/2 , 2 H 11/2 , and 4 F 7/2 , the absorption transitions of Er 3+ ions in tellurite glass connect with absorption bands centered about 1529, 974, 796, 652, 544, 522, and 486 nm [14,25], which are presented in Figure 8. Table 7 shows there is no overlap between the spectra and J-O parametrization.The small RMS confirms that the intensities of the experimental and theoretical oscillators are very similar.aterials 2023, 16, x FOR PEER REVIEW 12 metrization.The small RMS confirms that the intensities of the experimental and t retical oscillators are very similar.For the lanthanide series, we now know the J-O parameters.Since the intensiti the f-f transitions in lanthanides are ligand-dependent, the findings indicate the predi trends of the (Ω2, Ω4, Ω6) parameters with the rising of f-f electrons across the rare-e   Visible range absorption spectra were assigned, as seen in Figure 6.Considering the intricacy of the total of the 2S+1 LJ transitions, it was not surprising that calculating the J-O parameters was complex.F11/2 were measured experimentally and computed [23].As shown in Table 5, there was a high agreement between the experimental and calculated oscillator strengths and the J-O parameters, proving the accuracy of the J-O predictions.Consistent with previous research by authors such R. Van  For the lanthanide series, we now know the J-O parameters.Since the intensities of the f-f transitions in lanthanides are ligand-dependent, the findings indicate the predicted trends of the (Ω 2 , Ω 4 , Ω 6 ) parameters with the rising of f-f electrons across the rare-earth series.The RMSE measures how well the data fit the model.In addition, we compared the (Ω 2 , Ω 4 , Ω 6 ) calculations in our matrices to those in the scientific literature (Table 8) [8,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39].[39] The molecular nature of metal-ligand bonds has also been connected to the J-O parameters.Due to the matrix structure complex that these ligands are a part of, the Ω 2 is dependent on a hypersensitive transition.Due to the fact that f orbitals are far more insulated from the environment than metal d orbitals, consideration must be taken while inferring the spectroscopic and structural connection.On the other hand, the matrix plays an important role, because it provides a broad compositional field that changes with the glass transition, crystallization temperature, and melting temperature.Consequently, these variables affect the dimensions of intensity in different ways.Therefore, the parameters of intensity are still within the experimentally acceptable range [18].
The J-O parameter trend over the lanthanides in tellurite glasses is well recognized.When the number of f-f electrons is higher, the Ω 2 behavior tendency increases, which is similar to other matrices like fluorohafnate glasses and oxyfluoride glass ceramics.
The high oscillator strengths at the hypersensitive transitions may explain why the Ω 2 values of Nd 3+ and Dy 3+ ions are so large relative to the predicted trend.When the values of the individual matrix's U 2 2  U 2 2 elements are large, the resulting Ω 2 parameter are also large.Furthermore, it is difficult to determine the exact values of Ω 2 due to the overlap of bands in the UV region, as shown in Figures 4 and 6.This is because the observed and theoretical oscillator strengths for Nd 3+ and Dy 3+ are consistent.As a consequence, it is possible to derive many transitions from a single, complicated absorption band.
In fact, the predicted and experimental findings for the oscillator strengths of the hypersensitive transitions were more in agreement than those for the lesser oscillator strength of the UV transitions (i.e., Nd 3+ and Dy 3+ ).According to R. Van Deun et al. [8,18], the absorption spectra of Er 3+ exhibit strong, nonoverlapping absorption bands, equally scattered from the UV area to the NIR region; hence, the Ω 2 values for these spectra do not cause any complications for J-O calculations.The strength of the oscillator may be calculated, and the J-O parameters can be estimated.
For Sm 3+ , the transition spectra and computed modified J-O parameters exhibited good agreement, with low RMSE and non-negative parameter values for the predicted oscillator strengths.
The findings in Table 8 indicate that the trend towards a series that is suitable with the literature [18] decreases for the parameters Ω 4 and Ω 6 .The nuclear charge increased by 4f N causes lanthanide shell contraction, which causes a decrease in the radius integrations in the U 4,6 2  matrix elements, an observable decreasing tendency [22].
Covalence of the RE 3+ -F bond was investigated by comparing the findings to those of previous spectral studies published in the literature (Table 8).There was no obvious correlation between the spectral profile and the glass composition in our data.Therefore, it is not obvious that the spectral profile of the hypersensitive transition is dependent on the tellurite concentration, but the data clearly suggest that the intensity of the oscillator increases with the higher concentration.
The collective modes of local structures and heavy metal ion vibrations, such as the motion of Bi 3+ or Bi +3 cations in BiO 6 octahedral and/or BiO 3 pyramidal units, are responsible for the observed band labeled (A) around 163-188 cm −1 , which was observed when studying the structure of these glasses [5,15].Bi-O-Bi and Bi-O vibrations of BiO 6 octahedral units may be responsible for the band designated (B) at 237-303 cm −1 [40].
The collective modes of local structures and heavy metal ion vibrations, such as motion of Bi 3+ or Bi +3 cations in BiO6 octahedral and/or BiO3 pyramidal units, are resp sible for the observed band labeled (A) around 163-188 cm −1 , which was observed wh studying the structure of these glasses [5,15].Bi-O-Bi and Bi-O vibrations of BiO6 oc hedral units may be responsible for the band designated (B) at 237-303 cm −1 [40].The TeO4 axial bending vibration mode (Oac-Te-Oac) at corner sharing sites, wh combines the structure's equatorial oxygen atoms with axial oxygen atoms, is respons for the band designated (C) around 394-411 cm −1 in the sample.Sample TB4 does not clude a peak around 360 cm −1 , which may be attributed to either TeO3 tp or the E bond; therefore, its presence may have been hidden by the strong Raman response of TeO2 matrix or have been very low.Symmetrical or bending vibrations of Teeq-Oax connections at corner sharing sites in TeO4 [40,45]

Conclusions
Research on rare-earth ion-doped tellurite glass was performed.It was observed that, when the number of doped ions varied, unbridged oxygen formed, causing a change in density.The glasses we produced had excellent thermal stability (>100 • C), as shown by the thermal inverted.The measurements for the refractive index showed an extremely high value (n = 2.47).

Figure 1 .
Figure 1.Photography of the samples.

Figure 1 .
Figure 1.Photography of the samples.

Figure 4 .
Figure 4. Plot of (αhʋ) 1/2 against the energy of (a) a TB glass sample and (b) of doped glass sa for indirect band gap measurements.
the values of Eopt for each sample, with TB h the highest value and TB4 the lowest.The index of refraction n is one of the most important characteristics of o glasses.The refractive index values of prepared glass samples were obtained usin Dimitrov and Sakka relation, as depicted in Equation (11) [17] and tabulated in Tab

Figure 4 .
Figure 4. Plot of (αhʋ) 1/2 against the energy of (a) a TB glass sample and (b) of doped glass samples for indirect band gap measurements.

) 1 /
2 against the energy of (a) a TB glass sample and (b) of doped glass samples for indirect band gap measurements.

Figure 10 .
Figure 10.Peak deconvolution of Raman spectra of the (80-y) TeO 2 -20 BiCl 3 -y RE 2 O 3 (y = 0, 0.6% mol; RE = Nd, Sm, Dy, and Er) glass system.The TeO 4 axial bending vibration mode (O ac -Te-O ac ) at corner sharing sites, which combines the structure's equatorial oxygen atoms with axial oxygen atoms, is responsible for the band designated (C) around 394-411 cm −1 in the sample.Sample TB4 does not include a peak around 360 cm −1 , which may be attributed to either TeO 3 tp or the Er-O bond; therefore, its presence may have been hidden by the strong Raman response of the TeO 2 matrix or have been very low.Symmetrical or bending vibrations of Teeq-Oax-Te connections at corner sharing sites in TeO 4 [40,45] account for the band designated (D) at 453-503 cm −1 .Anti-symmetrical stretching of the continuous TeO 4 tbps network is responsible for the (E) band seen between 609 and 658 cm −1 [2,42].The (F) band at 757-854 cm −1 is due to Te-O and Te=O bond stretching vibrations in non-bridging oxygen in TeO 3 tps and TeO 3+1 polyhedra or Te 2 O 7 bridged tetrahedra (Te-O-Te antisymmetric stretch) [40,42].

Table 2 .
The glass transition temperature Tg, onset crystallization temperatures Tx, crystalliza temperatures Tp, thermal stability factor ΔT,

Table 4 .
The oscillator strengths and J-O parameters determined from the absorption spec TB1 glass.

Table
The oscillator strengths and J-O parameters determined from the absorption spectra of TB1 glass.

Table 4 .
The oscillator strengths and J-O parameters determined from the absorption spectra of TB1 glass.

Table 5 .
The oscillator strengths and J-O parameters determined from TB2 glass absorption spectra.

Table 4 .
The oscillator strengths and J-O parameters determined from the absorption spectra of TB1 glass.

Table 5 .
The oscillator strengths and J-O parameters determined from TB2 glass absorption tra.

Table 6 .
The oscillator strengths and J-O parameters determined from TB3 glass absorption tra.

Table 6 .
The oscillator strengths and J-O parameters determined from TB3 glass absorption spectra.

Table 4 .
The oscillator strengths and J-O parameters determined from the absorption spectra of TB1 glass.

Table 7 .
The oscillator strengths and J-O parameters determined from TB4 glass absorption tra.

Table 4 .
The oscillator strengths and J-O parameters determined from the absorption spectra of TB1 glass.
The oscillator strengths at the ground level 6
Table 9 lists the Raman band assignments, while Table 10 lists the observed Raman band positions for all compositions.Materials 2023, 16, x FOR PEER REVIEW ure 9).Table 9 lists the Raman band assignments, while Table 10 lists the observed band positions for all compositions.

Table 9 .
Peak positions in cm −1 of the prepared glasses.

Table 10 .
Assignments of deconvoluted Raman bands of the TB glass samples.

Table 9 .
Peak positions in cm −1 of the prepared glasses.