Enhanced Emission of Tellurite Glass Doped with Pr3+/Ho3+ and Their Applications

The shielding and spectroscopic properties of Pr+3 and Pr3+/Ho3+-codoped tellurite glass were investigated. The intensity parameters (Ω2 = 3.24-, Ω4 = 1.64-, Ω6 = 1.10 × 10−20 cm2) as well as the radiative lifetimes of 3F4 + 5S2 and 5I6 excited states of Ho3+ ions were equal to 301 μs and 3.0 μs, respectively. The former value appears to be much higher than that obtained from the lifetime measurement, indicating the presence of various energy transfer processes. The NIR spectrum of Pr3+/Ho3+-co-doped tellurite glass is dominated by strong Ho3+: 5I6 emission at around 1200 nm, being the result of the energy transfer from Pr3+ to Ho3+ ions. The shielding effectiveness of the prepared glasses showed good performance against high-energy photons. These findings suggest that the prepared glasses could be used in laser technology such as photodynamic therapy (PDT) treatment procedures and as shielding for radiation protection.


Introduction
Tellurite glasses with rare earth (RE) doping are promising materials for photonic applications such as solid-state lasers and lighting, optical amplifiers, and medical and sensing technologies. The applications of tellurite glasses are connected with their high transmittance from the visible to mid-infrared ranges (0.4-6 µm), high refractive index (n > 2), and low maximal phonon energy (~750 cm −1 ) [1,2]. One of the most frequently used dopants for tellurite glasses is the Ho 3+ ion, which exhibits both visible and infrared emissions due to its unique energy level structure [3]. In particular, these materials are expected to show an emission in the IR region at 1.2 µm, corresponding to the 5 I 6 → 5 I 8 transition. In addition, the emissions are also observed at 1.38 and 1.46 µm, for the 5 F 4 + 5 S 2 → 5 I 6 and 5 F 5 → 5 I 6 transitions, respectively. Emission from levels 5 I 6 → 5 I 8 and 5 F 4 + 5 S 2 → 5 I 5 of Ho 3+ ions may be promising for obtaining a signal band gain of 1.2-1.4 µm [4][5][6].
Ho 3+ ions can induce interesting emission and luminescence decays. Therefore, glasses doped with Ho 3+ ions exhibit visible green and red emissions at exited level ( 5 F 4 , 5 S 2 )→ 5 I 8 ,

Experimental Work
The core six tellurite glass samples were prepared by melting 25 g batches of highly pure (99.99%) chemicals in gold crucibles at 850 • C in an ambient atmosphere. The resulting material has the molar composition 78TeO 2 -10Nb 2 O 5 -5PbO-1PbF 2 -5Li 2 O-1La 2 O 3 . To prevent vaporization losses, a platinum plate was placed on top of the crucibles. While melting, the melts were periodically agitated to prevent inhomogeneity. The melts were then placed onto plates that had been warmed to 400 • C, generating layers that were a few mm thick, and these layers were then annealed between 320 and 340 • C. The concentrations of lanthanide ions (N Ln ) of Pr 2 O 3 and Ho 2 O 3 incorporated into the host matrix have been calculated by the equation reported in Ref [23]. The density of the prepared glasses was determined using Archimedes' law [23]. The glass samples were sliced and polished to a size of around 5'5'2 mm 3 for spectroscopic measurements. The M-2000 Woollam ellipsometer was used to collect the ellipsometric data, and the Perkin Elmer Lambda 900 spectrophotometer was used to capture the transmittance and reflectance spectra. The luminescence decay curves were obtained after a short pulse stimulation delivered by an optical parametric oscillator powered by a third harmonic of a Nd:YAG laser [24]. The photoluminescence spectra were measured using an Optron Dong Woo fluorometer system. Table 1 shows the sample code, composition, molar mass, density, and concentrations of lanthanide ions. The shielding parameters of the prepared samples such mass and linear attenuation coefficients (MAC and LAC), half-value layer (HVL), and mean free path (MFP), were investigated using MIKE software [25].

Shielding Properties
The possibility of photons interacting with a barrier is characterized as the mass attenuation coefficient (MAC) of a shielding material, and it is expressed as follows for a combination of elements or any chemical molecule [26].
where w i represents the fractional weight of individual components in each compound, and ρ indicate the density of material, µ/ρ is mass attenuation of the individual components. The LAC can then be estimated by using the following relationship: The average distance a photon can go through the barrier without interacting is known as the mean free path (MFP), and it is determined by the reciprocal of the linear attenuation [27]: The thickness of the interaction target at which the attenuated intensities account for 50% of the narrow photon beam intensity is defined by the half-value layer (HVL). The necessary thickness of shielding material is inversely proportional to the HVL value. The HVL can be calculated using the following equation [27]: Figure 1 shows the net absorption bands of Pr 3+ and Ho 3+ ions, obtained by subtraction of the monotonic background absorption of the glass matrix (shown for sample T0 in [28]) from the total absorption determined for samples TPr and TPrHo.

Absorption Spectra and Judd-Ofelt Analysis
As seen in Figure 1, the spectra of samples TPr and TPrHo show the existence of several single absorption bands attributed to transitions from the ground states of both ions, Pr 3+:3 H 4 and Ho 3+:5 I 8 , to subsequent excited states, as indicated elsewhere [29].
In addition, the spectra of sample TPrHo show overlapping absorption bands associated with transitions to excited levels of Ho 3+:5 I 7 and Pr 3+:3 F 2 in the NIR region as well as transitions to levels of Ho 3+:5 G 6 and Pr 3+:3 P 2 in the visible region.
One can see in Figure 1 five Ho 3+ absorption bands, that do not overlap with Pr 3+ bands allowing one to perform the standard J-O analysis for the former ion. However, it appears that such an analysis results in a negative, unphysical value of the Ω 2 J-O intensity parameter, due to the neglect of the strong Ho 3+ : 5 G 6 absorption band. In order to include this band, we have subtracted from the sample TPrHo absorption a contribution from the Pr 3+ absorption, which is equal to half of that measured for sample TPr, considering the difference in Pr 3+ ion concentrations between the two samples as shown in Table 1. For completeness' sake, we have also extracted the Ho 3+:5 I 7 absorption band, and both bands are shown in Figure 2. As seen in Figure 1, the spectra of samples TPr and TPrHo show the existence of several single absorption bands attributed to transitions from the ground states of both ions, Pr 3+:3 H4 and Ho 3+:5 I8, to subsequent excited states, as indicated elsewhere [29].
In addition, the spectra of sample TPrHo show overlapping absorption bands associated with transitions to excited levels of Ho 3+:5 I7 and Pr 3+:3 F2 in the NIR region as well as transitions to levels of Ho 3+:5 G6 and Pr 3+:3 P2 in the visible region.
One can see in Figure 1 five Ho 3+ absorption bands, that do not overlap with Pr 3+ bands allowing one to perform the standard J-O analysis for the former ion. However, it appears that such an analysis results in a negative, unphysical value of the Ω2 J-O intensity parameter, due to the neglect of the strong Ho 3+ : 5 G6 absorption band. In order to include this band, we have subtracted from the sample TPrHo absorption a contribution from the Pr 3+ absorption, which is equal to half of that measured for sample TPr, considering the difference in Pr 3+ ion concentrations between the two samples as shown in Table 1. For completeness' sake, we have also extracted the Ho 3+:5 I7 absorption band, and both bands are shown in Figure 2. It appears that the extracted absorption bands from Figure 2 are very similar to those determined for a single Ho 3+ -doped tellurite glass [30], justifying the extraction procedure.
Finally, we have applied the standard Judd-Ofelt theory to six electric dipole transi- It appears that the extracted absorption bands from Figure 2 are very similar to those determined for a single Ho 3+ -doped tellurite glass [30], justifying the extraction procedure.
Finally, we have applied the standard Judd-Ofelt theory to six electric dipole transitions specified in Table 2, calculating their oscillator strengths by numerical integration of the corresponding absorption bands; in order to minimize the root-mean-square deviation, the transition 5 I 8 → 5 I 7 has been omitted in the analysis due to a significant, magnetic dipole contribution to the oscillator strength and uncertainty connected with the extraction procedure [31]. The oscillator strength values of the prepared glass were calculated using Equation reported in Ref [23].  [28] The refractive index dispersion of samples T0 and TPr, obtained from ellipsometric data, is presented in our previous work [28], as being very well described by the Sellmeier model of the form n(λ) = [A + Bλ 2 /(λ 2 − C 2 ) − Dλ 2 ] 1/2 , where A, B, C, and D are the fitting parameters. Adopting the same procedure for sample TPrHo, the values of the fitting parameters have been found as A = 2.729, B = 1.764, C = 244.16 nm, and D = 2.52 × 10 −9 nm −2 . As for the reduced matrix elements for the electric dipole transitions, we have used the data from Ref. [32]. Table 2 shows the calculated Judd-Ofelt parameter values along with the root-mean square deviation (δ rms ).
The obtained values of the Ω i (I = 2,4,6) parameters follow the same pattern as those observed for different Ho 3+ -doped tellurite glasses and follow the same sequence, namely Ω 2 > Ω 4 > Ω 6 [29]. On the other hand, the sequence is different with Tellurite glasses doped with Pr +3 [24,28].
The J-O parameters have been used to estimate the transition probability W r of 5 I 6 (323 s −1 ), 5 S 2 (4549 s −1 ) and 5 F 4 (2060 s −1 ) excited states of Ho 3+ ions and subsequently the total radiative lifetimes τ rad = 1/W r . The levels 5 S 2 (lower) and 5 F 4 (higher) are very close to each other, leading to one absorption band, as shown in Figure 1. The occupation of these levels is governed by the Boltzmann factor, exp(-∆E/k B T), where ∆E is the energy separation between the levels, k B is the Boltzmann constant, and T is temperature. To calculate ∆E, we have fitted two Gaussians to the ( 5 S 2 + 5 F 4 ) absorption band, which yields ∆E = 128 cm −1 . The common transition probability for these levels is given by [33] where J = 2 and J = 4 are the total momenta of 5 S 2 and 5 F 4 excited levels, respectively.

Emission Spectra
In addition, the PL signal of both samples (in arbitrary units) has been divided by N Pr ; to illustrate the impact of Pr 3+ ion concentration (N Pr ) on the emission spectra as shown in Table 1. Emission spectra were obtained under identical conditions, permitting comparison of their relative intensities.
A significant number of excited states of Pr 3+ and Ho 3+ ions and their relatively high concentrations in the investigated samples create many possible radiative and non-radiative energy transfer (ET) processes between the Pr-Pr, Ho-Ho, and Pr-Ho pairs as discussed below. Figure 3 shows the visible PL spectrum for samples TPr and TPrHo under 445 nm (22,472 cm −1 ) excitation, corresponding to Pr 3+ : 3 H 4 → 3 P 2 and Ho 3+ : 5 I 8 → 5 G 6 absorption bands, as shown in Figure 1. When comparing the emission spectra from Figure 3, it is clear that the spectrum of sample TPrHo consists of many Pr 3+ emission bands that are completed with two Ho 3+ bands, namely with a relatively strong ( 5 F 4 + 5 S 2 )→ 5 I 8 emission at 18,290 cm −1 and a weak ( 5 F 4 + 5 S 2 )→ 5 I 7 emission at 13,250 cm −1 . With the exception of the 3 P 0 → 3 H 6 and 3 P 0 → 3 H 4 bands, many Pr 3+ emission bands are generally proportional to NPr, indicating that the concentration has been quenched by cross-relaxation and energy migration processes [30,34]. Similar cross-relaxation pathways result in numerous transitions between the energy levels of this ion in glasses doped exclusively with Ho 3+ ions [30,[35][36][37][38]. The energy level diagram of Ho +3 /Pr +3 ion codoped in the present host matrix were shown in Figure 4. Figure 5 displays the NIR emission spectra of the samples TPr and TPrHo, normalized as scale from the visible spectra in Figure 3.
( 5 F4+ 5 S2)→ 5 I7 emission at 13,250 cm -1 . With the exception of the 3 P0→ 3 H6 and 3 P0→ 3 H4 bands, many Pr 3+ emission bands are generally proportional to NPr, indicating that the concentration has been quenched by cross-relaxation and energy migration processes [30,34]. Similar cross-relaxation pathways result in numerous transitions between the energy levels of this ion in glasses doped exclusively with Ho 3+ ions [30,[35][36][37][38]. The energy level diagram of Ho+3/Pr+3 ion codoped in the present host matrix were shown in Figure  4.    concentration has been quenched by cross-relaxation and energy migration processes [30,34]. Similar cross-relaxation pathways result in numerous transitions between the energy levels of this ion in glasses doped exclusively with Ho 3+ ions [30,[35][36][37][38]. The energy level diagram of Ho+3/Pr+3 ion codoped in the present host matrix were shown in Figure  4.     Table 3 includes the lifetimes of the 3 P 0 excited state of the Pr 3+ ions as well as the predicted lifetime values and experimental data in order to compute the ET efficiency from these ions to Ho 3+ ions. The 3 P 0 Lifetimes of TPr are taken from our previous work [28]. The ( 3 F 4 + 5 S 2 ) lifetime of TPrHo was measured and calculated as shown in Table 3. The 5 I 6 lifetime is only calculated in the present study. Figures 6 and 7, respectively, show the excited levels of Ho 3+ :( 5 F 4 + 5 S 2 ) and Pr 3+ : 3 P 0 's PL decays. Since the decay data are non-exponential, we have established that the experimental lifespan is equal to the effective lifetime, which is defined as follows:   There are numerous potential energy transfer mechanisms between the ions when Pr 3+ and Ho 3+ ions are present in sample TPrHo at relatively high and comparable concentrations. As a result, the measured lifetime of Ho 3+ :( 5 F4 + 5 S2) emission is significantly   There are numerous potential energy transfer mechanisms between the ions when Pr 3+ and Ho 3+ ions are present in sample TPrHo at relatively high and comparable concentrations. As a result, the measured lifetime of Ho 3+ :( 5 F4 + 5 S2) emission is significantly shorter (5.49 μs) than that predicted from the J-O analysis (301μs; Table 3).  There are numerous potential energy transfer mechanisms between the ions when Pr 3+ and Ho 3+ ions are present in sample TPrHo at relatively high and comparable concentrations. As a result, the measured lifetime of Ho 3+ :( 5 F 4 + 5 S 2 ) emission is significantly shorter (5.49 µs) than that predicted from the J-O analysis (301µs; Table 3).

Lifetime
As was mentioned before while describing the sample's emission spectra, sample TPr has a high concentration of Pr 3+ ions, which results in an effective cross-relaxation (CR). When compared to the J-O radiative lifetime (9.43 µs [28]), the Pr 3+ : 3 P 0 effective lifetime is significantly reduced by the CR mechanism, going down to τ eff = 2.47 µs. The concentration of Pr 3+ ions in sample TPrHo is two times lower than in sample TPr, so one would expect that τ eff would be significantly higher and equal to 3.92 µs [28]. However, when the former sample is codoped with Ho 3+ ions, an additional energy transfer (ET) occurs between the two ions, which reduces the Pr 3+ : 3 P 0 lifetime to 2.75 µs.
The ET efficiency (η) from Pr 3+ to Ho 3+ ions can be estimated using the following equation, calculated as [29] where τ Pr-Ho and τ Pr are the effective lifetimes with and without Ho 3+ co-doping, respectively, for the same concentration of Pr 3+ ions. Using the value τ Pr = 3.92 µs, corresponding to N Pr =3.16×10 20 cm −3 , we have obtained the ET efficiency η = 29% that can be compared with the values 19 and 32.3% found for tellurite glasses doped with 1 mol% of Pr 3+ ions, and codoped with 0.5 and 1 mol% of Ho 3+ ions, respectively [28]. The observed increase of ET efficiency with the increasing N Ho /N Pr ratio is in accordance with the theoretical modeling of quantum cutting via a two-step ET [39].

5 I 8 → 5 I 6 Transition
The absorption cross-section (ACS) and emission cross-section (ECS) of the 5 I 8 ↔ 5 I 6 transition are the key characteristics for use in optoelectronics, thus we will focus on them.
The absorption cross-section (ACS; σ abs ) of the 5 I 8 → 5 I 6 transition was determined in the range of 1100-1250 nm by dividing the absorption coefficient by the Ho 3+ ion concentration. This makes it possible to use the McCumber formula to determine the emission cross-section (ECS; τ em ) of the 5 I 6 → 5 I 8 transition [40].
where h is the Planck constant., E mt is the mean transition energy between the 5 I 8 and 5 I 6 levels, which can be calculated by averaging the barycenter energies of the absorption and emission spectra. This results in E mt = 8519 cm −1 . As for the measured 5 I 6 → 5 I 8 emission, it is given in arbitrary units in Figure 5. To scale this emission, we have used the equation for ECS following the Füchtbauer-Ladenburg (F-L) approach and given by (see Ref [9]) with the branching ratio β = 0.91 and W r = 323 s −1 that were calculated for 5 I 6 → 5 I 8 emission from the J-O analysis. The ACS and ECS spectrums were calculated using Equations (8) and (9). The calculated spectrum is shown in Figure 8.
As shown in Figure 8, there is a relatively small shift (107 cm −1 ) between the peak value of ACS at 1167 nm (10,246 cm −1 ) and that of ECS at 1181 nm (10,163 cm −1 ). The McCumber and Füchtbauer-Ladenburg (F-L) curves are quite similar in shape but very different in magnitude; the peak value of σ F−L em (4.63 × 10 −21 cm 2 ) is about two times greater than that of σ MC em (2.18 × 10 −21 cm 2 ), suggesting effective ET from Pr 3+ to Ho 3+ ions, since the MC curve reflects emission of Ho 3+ ions in the absence of Pr 3+ ions, while the F-L curve represents the emission enhanced by codoping with the latter ions [39,40].
As shown in Figure 8, there is a relatively small shift (107 cm −1 ) between the peak value of ACS at 1167 nm (10,246 cm −1 ) and that of ECS at 1181 nm (10,163 cm −1 ). The McCumber and Füchtbauer-Ladenburg (F-L) curves are quite similar in shape but very different in magnitude; the peak value of (4.63×10 −21 cm 2 ) is about two times greater than that of (2.18 × 10 −21 cm 2 ), suggesting effective ET from Pr 3+ to Ho 3+ ions, since the MC curve reflects emission of Ho 3+ ions in the absence of Pr 3+ ions, while the F-L curve represents the emission enhanced by codoping with the latter ions [39,40].

Shielding Properties
Over a broad energy range, ranging from 0.5 to 15 MeV, the shielding effectiveness of the produced glasses was examined. Using MIKE software, the radiation parameters of the investigated glasses were estimated. The mass attenuation coefficient and linear attenuation coefficients were investigated in the intermediate and high photon energy ranges, ranging between 500 keV and 15 MeV. The results of the mass attenuation coefficient and linear attenuation coefficients of the prepared glasses were compared to those of commercially available standard materials coded RS-253 G18, RS-520, and RS-360 [41], as shown in Figure 9a,b. As illustrated in Figure 9, the values of MAC and LAC decrease slowly as the photon energy increases. This trend is in fact due to the dominance of Compton scattering, which is directly proportional to the atomic number and inversely proportional to the photon energy [42]. As the photon energy increases above 5 MeV, a slight increase in the MAC and LAC is observed. This trend is mainly due to the contribution of the pair production process, which is directly proportional to the square of the atomic number and directly proportional to the photon energy [43]. For example, as shown in Table 4, the prepared glasses' recoded LAC values at 6 MeV are 0.19588, 0.20125, and 0.20195 for T0, TPr, and TPrHo, respectively. As recoded, there is a slight increase in MAC and LAC values using different dopants; sample TPrHo recorded the highest values among the other prepared samples. In comparing the LAC values of the prepared glasses with some of the standard materials, namely RS-253 G18, RS-360, and RS-520, significant shielding performance was observed for the prepared glasses over the standard materials RS-253 G18 and RS-360 (0.069071 and 0.146893 at 6 MeV). On the other hand, the prepared glasses show

Shielding Properties
Over a broad energy range, ranging from 0.5 to 15 MeV, the shielding effectiveness of the produced glasses was examined. Using MIKE software, the radiation parameters of the investigated glasses were estimated. The mass attenuation coefficient and linear attenuation coefficients were investigated in the intermediate and high photon energy ranges, ranging between 500 keV and 15 MeV. The results of the mass attenuation coefficient and linear attenuation coefficients of the prepared glasses were compared to those of commercially available standard materials coded RS-253 G18, RS-520, and RS-360 [41], as shown in Figure 9a,b. As illustrated in Figure 9, the values of MAC and LAC decrease slowly as the photon energy increases. This trend is in fact due to the dominance of Compton scattering, which is directly proportional to the atomic number and inversely proportional to the photon energy [42]. As the photon energy increases above 5 MeV, a slight increase in the MAC and LAC is observed. This trend is mainly due to the contribution of the pair production process, which is directly proportional to the square of the atomic number and directly proportional to the photon energy [43]. For example, as shown in Table 4, the prepared glasses' recoded LAC values at 6 MeV are 0.19588, 0.20125, and 0.20195 for T0, TPr, and TPrHo, respectively. As recoded, there is a slight increase in MAC and LAC values using different dopants; sample TPrHo recorded the highest values among the other prepared samples. In comparing the LAC values of the prepared glasses with some of the standard materials, namely RS-253 G18, RS-360, and RS-520, significant shielding performance was observed for the prepared glasses over the standard materials RS-253 G18 and RS-360 (0.069071 and 0.146893 at 6 MeV). On the other hand, the prepared glasses show a slightly lower performance compared with RS-520, this is obviously due to the higher lead oxide content in the RS-520 (70%) compared to 5% lead oxide in sample TPrHo (5%) in Table 4. The recoded MAC and LAC values of the prepared glasses at different energies range between 500 keV and 15 MeV. The good performance of the prepared glasses in terms of good optical, physical, and shielding properties such as good thermal stability, chemical durability, high values of linear and nonlinear refractive index, and shielding effectiveness are all due to the fact that the tellurite-based glass doped with suitable metal oxides and rare earths can form a high-efficiency glass material that can be used in different applications. [2,12,14]. range between 500 keV and 15 MeV. The good performance of the prepared glasses in terms of good optical, physical, and shielding properties such as good thermal stability, chemical durability, high values of linear and nonlinear refractive index, and shielding effectiveness are all due to the fact that the tellurite-based glass doped with suitable metal oxides and rare earths can form a high-efficiency glass material that can be used in different applications. [2,12,14].  The HVL represents the absorbance thickness necessary to halve the photon intensity. The mean free path (MFP) is the average distance a photon travels before colliding with a particle in a medium. The HVL and MFP values show how well the gamma radiation is slowed down by the shielding glass material. The HVL and MFP are inversely proportional to the shielding material's linear attenuation coefficient (LAC); the lower the value, the more effective the material as a shield. The HVL and MFP of the prepared glasses are illustrated in Figure 10a,b. As shown in Figure 10a, there are two fundamental features of the HVL: First, the HVL of all prepared glasses increases with the increasing energy until reaching 6 MeV, it then decreases slowly with the increasing photon energy. For instance, as shown in Table 4, the recorded values at 6 MeV are equal to 3.54, 3.44, 3.43, 10.0, 4.71, and 3.08 cm for T0, TPr, TPrHo, RS254G18, RS360, and RS520, respectively. The recorded increase in HVL is caused by the decrease in the probability of interaction with high-energy photons, which increases the probability of penetrating the samples and necessitates a thicker sample to absorb the same amount of radiation. The second property of the HVL is that it decreases as the absorber density increases; at 6 MeV, the order of the HVL results is as follows: RS520 < TPrHo < TPr < T0 < RS360 < RS254G18. As discussed  The HVL represents the absorbance thickness necessary to halve the photon intensity. The mean free path (MFP) is the average distance a photon travels before colliding with a particle in a medium. The HVL and MFP values show how well the gamma radiation is slowed down by the shielding glass material. The HVL and MFP are inversely proportional to the shielding material's linear attenuation coefficient (LAC); the lower the value, the more effective the material as a shield. The HVL and MFP of the prepared glasses are illustrated in Figure 10a,b. As shown in Figure 10a, there are two fundamental features of the HVL: First, the HVL of all prepared glasses increases with the increasing energy until reaching 6 MeV, it then decreases slowly with the increasing photon energy. For instance, as shown in Table 4, the recorded values at 6 MeV are equal to 3.54, 3.44, 3.43, 10.0, 4.71, and 3.08 cm for T0, TPr, TPrHo, RS254G18, RS360, and RS520, respectively. The recorded increase in HVL is caused by the decrease in the probability of interaction with high-energy photons, which increases the probability of penetrating the samples and necessitates a thicker sample to absorb the same amount of radiation. The second property of the HVL is that it decreases as the absorber density increases; at 6 MeV, the order of the HVL results is as follows: RS520 < TPrHo < TPr < T0 < RS360 < RS254G18. As discussed before, the prepared glasses have LAC values higher than standard materials RS360 and RS254G18, which explain the lower values recorded for the prepared glasses compared with the standard materials. Due to the toxicity of lead oxide, the prepared glasses have a better likelihood of being utilized as an alternative shielding material in medical applications such shielding glass windows and shielding materials used directly on patients undergoing X-ray examinations. before, the prepared glasses have LAC values higher than standard materials RS360 and RS254G18, which explain the lower values recorded for the prepared glasses compared with the standard materials. Due to the toxicity of lead oxide, the prepared glasses have a better likelihood of being utilized as an alternative shielding material in medical applications such shielding glass windows and shielding materials used directly on patients undergoing Xray examinations. The shielding effectiveness of the prepared glasses can also be investigated in terms of radiation protection efficiency (RPE) [44]. RPE% = 1 − e (10) Figure 11 shows the RPE percentage of the prepared glasses with a thickness of 10 cm at photon energies ranging between 0.1 and 10 MeV. As shown in Figure 11, the RPE decreases with the increasing energy. For instance, the RPE percent decreased from 100 to 87.2% for T0, 100 to 87.9% for TPr, 100 to 88% for TPrHo, from 100 to 45.4% for RS-253G18, from 100 to 79.3% for RS-360, and from 100 to 91.5% for RS-520. As shown in Figure 11, the prepared glasses have good shielding efficiency compared to RS-254G18 and RS-360 and are slightly lower than RS-520. The 10 cm thickness of the prepared glasses has a shielding efficiency above 90% for energies up to 10 MeV. The shielding effectiveness of the prepared glasses can also be investigated in terms of radiation protection efficiency (RPE) [44]. Figure 11 shows the RPE percentage of the prepared glasses with a thickness of 10 cm at photon energies ranging between 0.1 and 10 MeV. As shown in Figure 11, the RPE decreases with the increasing energy. For instance, the RPE percent decreased from 100 to 87.2% for T0, 100 to 87.9% for TPr, 100 to 88% for TPrHo, from 100 to 45.4% for RS-253G18, from 100 to 79.3% for RS-360, and from 100 to 91.5% for RS-520. As shown in Figure 11, the prepared glasses have good shielding efficiency compared to RS-254G18 and RS-360 and are slightly lower than RS-520. The 10 cm thickness of the prepared glasses has a shielding efficiency above 90% for energies up to 10 MeV.

Conclusions
The spectroscopic properties of Pr 3+ -doped and Pr 3+ /Ho 3+ -co-doped multicomponent tellurite glass were investigated. Analysis of experimental data shows that there is energy transfer (ET) from Pr 3+ to Ho 3+ ions, which increases the emission of the latter ions by a Figure 11. RPE% with photon energy (in MeV) of the prepared glasses.