Introduction

The rare-earth (RE) doped materials have gained considerable attention owing to their potential applications in many fields, like medicine, optoelectronics, and telecommunication (optical fibers, lasers, and amplifiers) because RE ions exhibit emission transitions in 4f-4f or 4f-5d, additionally their unique electronic configuration from the ultraviolet region to the infrared region makes them to act as an excellent activator to emit sharp luminescence [1,2,3]. In particular, glasses doped with RE ions have gained significant attention for the development of Solid-State Lighting devices (SSL). The SSL technology is used in many lighting applications because of its advantages like durability, energy saving and eco-friendly [4]. In SSL, white light-emitting diodes (wLEDs) are an interesting possible substitute for fluorescent lamps because of their advantageous properties such as transparency, thermal stability, and low cost. Currently, blue or near-ultraviolet LED chips are used to excite phosphors (YAG: Ce3+, for example) in epoxy resin to provide white light. To achieve great brightness, however, the output power of the LEDs must be raised, which raises the chip's temperature. The resin can break down as a result of the temperature rise, which would lower the light's quality and intensity. Since they may be made in the form of a lens, luminescent materials doped with trivalent RE ions can be utilized to replace the phosphor particles to promote direct encapsulation of the LED chip [5].

On the other hand, the RE ions are using to replace the concretes [6] which are opaque and unclear to visible light, as alternative gamma ray shielding materials for various uses in high energy physics applications and nuclear waste management. The gamma rays which may lead to increase the risks for cancer, damage to human cells, and environmental effects. Therefore, the use of reliable shields is fundamental. Radiation shields are the most widely used materials because of their high density, good structural properties, and cost efficiency. Although lead is a very efficient shielding material but it is highly toxic and harmful to the environment; therefore, the present research is focused on non-toxic alternatives [7]. Numerous studies have been reported to replace the lead-based glass with different types of glass matrices like borates [8], silicates [9], phosphates [10], tellurites [11], etc., borate glasses are well-suited application for the prepared glasses [12,13,14].Boric acid (B2O3) is one of the excellent glass former in oxide materials because it has a high glass-forming trend and exhibits unique advantages, like minimum dielectric constant, ease of formation, low melting point, low cost, high RE ion solubility, and good transparency. Borate glasses are suitable for a variety of applications in fiberglass as they tend to reduce thermal expansion and resist thermal shock at high temperature. However, the main drawback of borate glasses is that, they possess a phonon energy of approximately 1300 cm−1, which is relatively quite high because the presence of lightweight which possess relatively high phonon energy. Such high phonon energies increase nonradiative loss through the multiphonon relaxation process. Heavy metal oxides like bismuth, tellurite, tungsten, and antimony have attracted attention because of their relatively low phonon energies, high polarizabilities, and high refractive indices [15]. In addition to the this, alkali fluorides such as NaF and LiF in the glass minimizes the non-radiative energy loss and decreases the phonon energy. Such alkali fluorides also help to remove the -OH groups present in the borate glasses. In addition, Aluminum Oxide (Al2O3), as a glass modifier, provides mechanical strength to glass and improves its optical response. The thermal and chemical properties also enhanced the emission properties of the prepared glass samples [16]. By adding the Al2O3 to a borate glass matrix it can form the AlO4 and AlO6 units [17].

Among lanthanides, Dysprosium ions (Dy3+), is a promising ion for white-light devices and visible-laser applications. It has distinct emission bands between the visible and near-infrared regions, which lend themselves to a variety of interesting optical properties. Due to electronic transitions at 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, and 4F9/2 → 6H11/2, Dy3+ ions primarily exhibit two strong emission bands, which are pure magnetic dipole transition at blue (470–500 nm) and pure electric dipole transition at yellow (570–600 nm) regions, as well as one weak red emission band (660–700 nm). Among these, the hypersensitive transition 4F9/2 → 6H13/2 is strongly affected by the environment. Emission of white light at a regulated yellow to blue (Y/B) ratio can be achieved by adjusting the concentration of dysprosium ions in a host matrix and adjusting excitation wavelength. The Y/B ratio also provides information on the Dy3+ -O2− ion environment in the nearby regions of the dysprosium ions, such as the degree of covalence. Both visible and near-infrared solids state lasers can be created through glasses doped with Dy3+ ions [18, 19].

In the present work, we synthesized the Dy3+ ions activated 60B2O3-10Sb2O3-10Al2O3-10NaF-(10-x) LiF-xR.E (OFSbB) glass samples were synthesized and characterized them by using XRD, FT-IR and optical properties such as absorption, luminescence spectra and decay time measurements. Evaluation of Judd-Oflet (J-O) intensity parameters and their trends, as well as physical parameters, were investigated with respect to Dy3+ concentration. The optical bandgap energy was estimated using Tauc’s plot for the indirect and direct transitions from the absorption data. Under excitation at 351 nm, the yellow-blue (Y/B) intensity ratio results in the application of white-light-emitting devices. The PSD software was used to investigate OFSbBDy glasses gamma-ray shielding parameters, including the Effective Atomic Number, Linear Attenuation Coefficient, Half Value Layer, Tenth Value Layer, Mean Free Path, Mass Attenuation Coefficient, and Exposure Buildup Factor.

Experimental Approach

Synthesis

The Melt-quenching method was used to synthesize the Dy3+ ions-doped glass with a 60B2O3-10Sb2O3-10Al2O3-10NaF-(10-x) LiF-xDy2O3 composition (where, x = 0.1, 0.5, 1.0, 1.5, 2.0, 2.5 mol %). The prepared glasses are referred to as OFSbBDy0.1, OFSbBDy0.5, OFSbBDy1.0, OFSbBDy1.5, OFSbBDy2.0, and OFSbBDy2.5, depending on the Dy-ion concentration from 0.1 to 2.5mol% respectively. All the chemicals were weighed using an electrical weighing balance with an appropriate molecular weight. After weighing, the chemical composition was ground into a fine powder using an agate mortar and pestle. The batch materials, which were placed in silica crucibles and heated for ten minutes at 1200 °C in an electric furnace, had a stoichiometric composition of approximately 8 g. The melt was kept homogeneous by being stirred every three minutes. To eliminate the internal thermal stress caused by the quenching process, the melt was quenched in a brass mold and plates that had been preheated and then annealed for two hours at 500 °C. The prepared glasses had a 2 mm thickness and were transparent.

Sample Characterization

Using Cu K (λ = 1.5405Å) radiation, an XRD analysis of the prepared glasses amorphous nature was performed on PANalytical EMPRYREAN diffractometer. The densities and refractive index of the glass samples were measured using Archimedes rule and Brewster’s angle method respectively. FT-IR spectra of the glass samples were recorded using a JASCO FT/IR- 4700 spectrometer. A JASCO V-670 UV–vis-NIR spectrometer was utilized for the recording of the absorption spectra. Using a JASCO FP-8300 spectrofluorometer, excitation, PL spectra and PL decay curves of the as prepared glass samples were recorded at room temperature. The characteristics of photon shielding for the OFSbBDy glasses were computed using the PSD/Phy-X software [20].

Results and Discussion

Structural Analysis

X-ray Diffraction

Figure 1 shows the patterns of X-Ray Diffraction at the different concentrations of Dy3+ ions-activated OFSbB glass samples recorded in the 2θ range of 20–80˚ on a PANalytical EMPYREAN diffractometer with Cu Kα (λ = 1.5405Å) radiation. In general, non-crystalline materials do not exhibit sharp peaks because of the nonperiodic arrangement of atoms in these solids, which does not satisfy the diffraction condition [21]. The prepared glass samples exhibited a broad hump at approximately 27°, indicating the presence of the BO3 group [5].

Fig. 1
figure 1

The X-Ray Diffraction patterns of the undoped and doped OFSbBDy glass samples

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Fourier Transform Infrared Spectroscopy

FT-IR plays an important role in determining the structural properties of the as prepared glass samples. Figure 2 represents the FT-IR spectra of Dy3+ ions-doped and un-doped OFSbB glass samples, which were recorded in the wavelength range from 450 to 3500 cm−1. The BO3 group is present, as an evidenced by the peak at 512cm−1. The bending vibrations of the BO – O– BO4 bonds is attributed due to the peak at 688cm−1. The peak at 891 cm-1 corresponds to the stretching vibrations of the tetrahedral BO4−1 units. The peak at 1047 cm−1 indicates the pentaborane group. The peaks at 1209 cm−1 represent the B-O-B bending vibrations in the tetrahedra corresponding to boron-tetrahedral units. The peak at 1335 cm−1 represents the stretch vibration between Boron-Oxygen bonds of the BO3 unit, which also results about the link between oxygen and different connecting diverse groups like orthoborate, metaborate and pyroborate. The peak at 2345 cm−1 indicates the presence of hydrogen bonds in the prepared glasses. The peak at 3057 cm−1 indicates the presence of the OH group [22,23,24,25].

Fig. 2
figure 2

The Fourier transform infrared (FTIR) spectra of the Dy3+ ions doped into the OFSbB glass samples

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Physical Parameters

Table 1 describes Physical parameters of Dy3+ ions doped OFSbB glasses like refractive index(n), density, RE ion concentration(N), average molecular weight(M), polaron radius(rp), inter-ionic distance(ri), and field strength(F) of the prepared glasses. The OFSbB glasses density increased with an increase in Dy3+ ions concentration. The density increased because of the increase in the molar mass and modifications of the BO3 triangles in to BO−4 tetrahedra. The density depends on the alkali type and alkali earth modifier, which occupy the interstitial positions in the glass network. The Li+ ion connects with the glass former cations, that is with B3+ ions, and enhances ring-type structures and coordination numbers, which also leads to a increase in density because of the presence of Non-Bridging Oxygen (NBO) atoms in dysprosium oxide. The refractive indices of the glasses increased with increasing Dy3+ ions concentration because the polarizability of oxide increase with rare earth ions and also related to the density. The prepared glasses result the low molar electronic polarizability value results the increase in the glass network stability because the molar polarizability connected to macro and micro, physical, chemical properties like UV absorption, chemical stability [14, 26].

Table 1 Physical parameters of Dy3+ ions doped OFSbB glasses
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Absorption Spectral Analysis

Figure 3 shows the absorption spectral data of the Dy3+ ions-doped OFSbB glasses, which were recorded at room temperature from the ultraviolet–visible to near-infrared region. The absorption spectra show twelve peaks that are arising due to f-f transition from the ground energy state 6H15/2 to various higher energy states of the doped dysprosium ions. The twelve electronic transitions of the absorption bands from 6H15/2 ground state are 4M15/2, 6P5/2, 4I13/2, 4G11/2, 4I15/2, 4F9/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2, 6F11/2, 6H11/2 with the energies 350, 364, 387, 426, 451, 473, 683,753, 802, 901, 1092, 1275 and 1684 nm respectively. All electronic transitions were identified according to a report available in literature [27]. The resultant band peak intensity exhibiting high energy in the UV region is weak because of less absorption, and the low-energy near-infrared region (NIR) exhibits a strong absorption titled host matrix. The Dy3+ ions electronic configuration is 4f9, which results in a ground state multiplet (6H), a high-intensity band at 1275 nm in the near-infrared region, and free ions in the ultraviolet region because of the overlapping of different 2S+1LJ levels. The spectra exhibited high intensity because of the hypersensitive nature of the 6H15/2 → 6F11/2 electronic transition, and obeyed the selection rules |∆S|= 0, |∆L|≤ 2, and |∆J|≤ 2 [28]. The electronic transition between the ground state (6H15/2) and excited states (6H, 6F) exhibited sharp and intense bands, owing to their spin-allowed nature.

Fig. 3
figure 3

The absorption spectra Dy3+ ions doped OFSbB glass samples

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Nephelauxetic Effects and Bonding Parameters

From the optical absorption spectra, the bonding nature of Dy-O in the OFSbB glass was determined. The nephelauxetic ratio (β) and the bonding parameter (δ) studies were used to determine the Dysprosium ion ligand’s bonding nature. The following equations are used to determine the Nephelauxetic ratio:

$$\upbeta =\frac{{\mathrm{\vartheta }}_{{\text{c}}}}{{\mathrm{\vartheta }}_{{\text{a}}}}$$
(1)

where, \({\mathrm{\vartheta }}_{{\text{c}}}\) is the wavenumber (cm−1) of a specific shift of the rare earth ions & \({\mathrm{\vartheta }}_{{\text{a}}}\) stands the wavenumber (cm−1) for the similar shift of an aqua ion. The δ is calculated by the following equation.

$$\updelta =\frac{1-\overline{\upbeta } }{\overline{\upbeta } }$$
(2)

Here, \(\overline{\upbeta }\) is the average of β value. `based upon the environment of δ results either positive or negative which indicates the covalent or ionic nature if bonding. The bonding parameter of the prepared Dy3+ ions-doped OFSbB glass was negative, -0.936, -0.932, -0.930, -0.929, -0.924, and -0.923 for 0.1,0.5,1.0,1.5,2.0 and 2.5 mol% indicating ionic bonding. It indicates that when the concentration of RE ions increases, the ligand network surrounding the RE ions changes. The number of NBO’s in the glass matrix, which are reason for the large changes in bonding parameter values, is also influenced by the doping concentration. The prepared glass samples, a decrease in ionicity corresponds to a reduction of bonding defects.

Optical Bandgap Analysis

Optical bandgap analysis was used to determine the bandgap between the conduction and valence bands in the oxide glasses. The nature of the glass structure and chemical bonding can be explored by analyzing the optical absorption spectral transitions [27, 29, 30]. By calculating the absorption coefficient α(ν), information about the induced transitions, such as direct and indirect allowed transitions, can be obtained. From the Davis and Mott theory, the following expression is used to evaluate the absorption coefficient [31].

$$\mathrm{\alpha h\nu }={\text{B}}{\left(\mathrm{h\nu }-{{\text{E}}}_{{\text{g}}}\right)}^{{\text{n}}}$$
(3)

where B is the band tailing parameter, Eg is the bandgap energy & n = 1/2 or 2, depends upon either indirect allowed transition or direct allowed transition, respectively. By using Tauc plot ((αhν)1/n vs. hν) the Eg values of the OFSbBDy glasses were determined through extrapolating the linear portion of the curve. Figure 4 represents the Tauc plot for indirect (n = 1/2) and direct (n = 2) transitions of the prepared glasses.

Fig. 4
figure 4

The indirect band gap of Dy3+ ions doped OFSbB glass samples. The inset shows direct band gap of Dy3+ ions doped OFSbB glass samples

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Estimation of Oscillator Strengths and Judd–Ofelt Intensity Parameters

The oscillator strengths are determined using the J–O theory, which explains the strength of the absorption peaks of RE ions. This determines the integration of the area under the curve of each observed band. Using the equation given below, the experimental oscillator strength(fexp) was calculated as follows:

$${f}_{exp}=4.318\times {10}^{-9}\int \varepsilon \left(v\right)dv$$
(4)

Here, Ɛ(ν), ν addresses the molar absorption of the peak(cm−1), frequency of specific band.

Additionally, the following formula can be used to estimate the calculated oscillator strength(fcal) during the primary and final state transitions [32, 33]:

$${{\text{f}}}_{{\text{cal}}}=\frac{8{\uppi }^{2}{\text{mc}}}{3{\text{h}}}\frac{{\left({{\text{n}}}^{2}+2\right)}^{2}}{9{\text{n}}}\frac{\upnu }{\left(2{\text{J}}+1\right)}\sum_{\uplambda =\mathrm{2,4},6}{\Omega }_{\uplambda }\left(\mathrm{\psi J}\text{||}{{\text{U}}}^{\uplambda }\text{||}{\uppsi }^{\mathrm{^{\prime}}}{{\text{J}}}^{\mathrm{^{\prime}}}\right)^2$$
(5)

The plank constant, electron mass, refractive index, and wavenumber (in cm−1) are all represented here by h, m, n and ν respectively. The angular momentum from the ground start to the excited state is represented by J (J = L + S); the absorption band’s Lorentz local field correction is (n2 + 2)2/9n; the host-dependent J-O intensity parameters and Uλ are the host-independent elements of the unit tensor square matrix. The following expression is used to evaluate the quality of fitting between the fexp and fcal data using root mean square deviation(δrms). The following expression is used to evaluate the quality of fitting between the fexp and fcal data using δrms.

$${\updelta }_{{\text{rms}}}=\sqrt{\frac{\sum {\left({{\text{f}}}_{{\text{exp}}}-{{\text{f}}}_{{\text{cal}}}\right)}^{2}}{{\text{N}}}}$$
(6)

where N represents the level. Table 2 shows the fexp, fcal and δrms values of the as prepared glass samples. The three calculated J-O intensities Ωλ(λ = 2,4,6) parameters are shown in Table 3. The parameters demonstrate nature of the local arrangement and bonding nature of the RE ions. From the Table 3, the evaluated Ωλ values results the same trend (Ω2 > Ω6 > Ω4) for all the titled glasses. From Jorgensen and Reisfeld theory [34], the covalent valence of the metal–ligand bond and the asymmetry of the ion sites in the ligand field around the Dy3+ ions affect the Ω2 parameter, while Ω4 and Ω6 depend on the viscosity of the medium and rigidity of medium. The Ω6 specifies the rigidity and a lower polarizability. Moreover, the determined Ω6 value indicates strong ionic network coupling and also results merging the opposite similarity energy levels. This remains vital increase to emission intensity the Dy3+ ions and keeps the thermal stresses low in order to achieve the thermal equilibrium of the quantum efficiency. The large value of Ω2 comparing with the Ω6 indicates the large asymmetry around the Dy3+ ions and closes the binding of the ligand ions. Moreover, the Ω2 value highly depends upon the sensitive transitions and provides the information on the nature of the Dy-O bonds. Higher oscillator strengths of hypersensitive transitions lead to maximum values of Ω2. The prepared glasses typically have Ω2 values that lies between in the range of Ω6 and Ω4 for the oxyfluoride glass. As we see that Ω2 increases until OFSbBDy0.5 glass greater and confirming the high asymmetry ligand field around the Dy3+ ions of the prepared glass. The J-O values results are compared with published work which is shown in Table 3 [19, 35,36,37,38].

Table 2 The oscillator strength (fexp and fcal X 10–6), rms deviation (δrms × 10–6) of the OFSbBDy glasses for different absorption bands
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Table 3 Comparison of J-O intensity parameters (Ω2, Ω4, Ω6 × 10–22 cm2) between OFSbBDy glasses and different reported Dy3+ ions doped glasses
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Photoluminescence Spectra

PL spectral studies of the Dy3+ ions doped OFSbB glasses were recorded and which are represented in the Figs. 5 and 6. Figure 5 The excitation spectra were in the range of 320 nm to 500 nm, and the emission spectra (Fig. 6) were in the range of 450 nm to 750 nm. At an emission wavelength of 573 nm, the peaks of the excitation bands located at 325, 338, 351, 364, 387, 427, 452, and 474 nm were related to transitions from 4M17/2, 6P7/2, 6P5/2, 4I13/2, 4G11/2, 4I15/2, and 4F9/2. Amongst these transitions, the 6H15/2 → 6P7/2 band at 351nm was relatively more intense than the other transitions. The results of the two highly intense bands at 480 nm(blue), 575 nm (yellow) and one less intense band at 663nm (red) corresponding to the transitions from the excited level 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 4H11/2 respectively. The Fig. 7 represents the variation of emission intensities of OFSbBDy0.5 glass excited at different excitation wavelengths. From the emission spectra, it is observed that luminescence intensity increases up to 0.5 mol% of Dy2O3 and decreases beyond because of concentration quenching effect. The concentration quenching effect is the result of the Dy-Dy distance, which occurs with increasing Dy2O3 concentration. The reduction in Dy-Dy distance shows resonant energy transfer (RET), which is otherwise called “energy migration” and the cross-relaxation (CR) energy transfer process between Dy3+ donor ions and acceptor ions. In Fig. 8, the Dy3+ ions partial energy level diagram and the RET, which corresponds to the PLE and PL transitions (6H15/2 → 6H15/2: 4F9/2) as well as CR (6H15/2 → 6F5/2: 6F9/2), (4F9/2: 6H15/2 → 6F3/2: 6F11/2) [39].

Fig. 5
figure 5

The excitation spectra of Dy3+ ion doped OFSbB glass samples

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Fig. 6
figure 6

The emission spectra of Dy3+ ion doped OFSbB glass at an excitation wavelength 351 nm. The inset shows the Yellow-blue (Y/B) intensity ratio of Dy3+ ions doped OFSbB glasses

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Fig. 7
figure 7

The emission spectra of Dy3+ ion doped OFSbB glass at an excited at 351 nm,375 nm and 405 nm wavelengths

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Fig. 8
figure 8

The partial energy level diagram of Dy3+ ions doped OFSbB glass samples

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Among all the above-mentioned transitions of the PL spectra, the transition at 4F9/2 → 6H15/2 is allowed magnetic dipole and the transition at 4F9/2 → 6H11/2 is forced electric dipole in nature [40]. The relationship between these two transitions indicates the nature of the dysprosium-oxygen bond by determining the ratio of yellow to blue, the degree of covalence between Dy-O ions increases with its value. In addition, for studying the symmetry shifts in Dy3+ ions, an important parameter is the yellow-to-blue intensity ratio (Y/B) which is shown inset of Fig. 6. The Y/B intensity ratios were 1.11,1.56,1.48,1.38,1.55, and 1.54, corresponding to the OFSbBDy0.1, OFSbBDy0.5, OFSbBDy1.0, OFSbBDy1.5, OFSbBDy2.0 and OFSbBDy2.5 glasses. The increase in the Y/B ratio indicated an increase in the covalent nature of the Dy-O bond. This indicates higher structural disorder around the Dy3+ ions [26, 27].

Radiative Properties

Following the expressions reported in the literature [41].The radiative properties have been calculated using J-O Parameters which includes effective bandwidths, radiative lifetimes (τR), radiative transition probabilities (AR), Stimulated emission cross-sections (σse) and branching ratios (βexp). The AR values influenced by the J-O intensity parameters and the energy gap between the initial and terminal levels, to determine the radiative relaxation of an excited state to all its lower levels

$$\tau {\text{R}}=\frac{1}{{{\text{A}}}_{\uptau }(\mathrm{\psi J})}$$
(7)

where AT denotes the total probability of transition which is the summation of transition probability values for a potential transition. The branching ratio (βR) is the basic parameter for the designing the laser since it portrays the chance of accomplishing the stimulated emission from any specific transition. The value for the potential laser activity must be greater than 0.5. The following expression can be used to determine the value of R from the total transition probability (AT) that corresponds to the emission and excited level to the lower level

$${\upbeta }_{{\text{R}}}= \frac{{{\text{A}}}_{{\text{R}}}(\mathrm{\psi J},{\uppsi }^{\mathrm{^{\prime}}}{{\text{J}}}^{\mathrm{^{\prime}}})}{{{\text{A}}}_{{\text{T}}}(\mathrm{\psi J})}$$
(8)

The higher branching ratio of the 4F9/2 → 6H13/2 shift among the observed emission shifts indicates that it is suitable for its lasing action. From the Table 5, the observed βexp values for each prepared glasses tend to be 6H13/2 > 6H15/2 > 6H11/2 which indicates that yellow emission is predominant. As a result, the prepared glasses are promising materials for visible yellow laser applications. Laser execution is highly dependent upon the σse which lies between the primary level (ΨJ) and the concluding level (Ψ'J’) with possibility AR is calculated as follows

$${\upsigma }_{{\text{se}}}\left(\mathrm{\psi J},{\uppsi }^{\mathrm{^{\prime}}}{{\text{J}}}^{\mathrm{^{\prime}}}\right)=\left(\frac{{\uplambda }_{{\text{p}}}^{4}}{8\mathrm{\pi \sigma }{{\text{n}}}^{2}\Delta {\uplambda }_{{\text{p}}}}\right){{\text{A}}}_{{\text{R}}}(\mathrm{\psi J},{\uppsi }^{\mathrm{^{\prime}}}{{\text{J}}}^{\mathrm{^{\prime}}})$$
(9)

where, \({\uplambda }_{{\text{P}}}\) is the emission lines peak wavelength and \({\Delta }_{\mathrm{\lambda eff}}\) is the effective bandwidth of the emission band, The effective bandwidth is determined by integrating the luminescence line’s intensity and dividing it by the intensity at the peak wavelength. The outcome for the radiative properties is recorded in Table 4. The optical gain bandwidth (σse × Δλp) and optical gain (σse × τR) values fundamental for manufacturing lasers and optical materials [42]. For the 4F9/2 → 6H13/2 transition, OFSbBDy0.5 glass has relatively higher values for gain bandwidth and optical gain parameters than the other prepared glasses which is shown in Table 5, This indicates the suitability of OFSbBDy0.5 glass for the visible laser and fiber amplifiers. [30, 35, 43,44,45,46,47,48,49].

Table 4 The Radiative transition probability (As−1), radiative branching ratios (βR) and stimulated emission cross-section (σse) (10–22 cm2) for the emission transitions of Dy3+ ions doped OFSbB glasses
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Table 5 Emission peak wavelength(λp) (nm), effective band width (Δλp) (nm), stimulated emission cross-section (σse) (10–22 cm2), gain band width (σse x Δλp) (10–28 cm3) and optical gain (σse x τR) (10–25 cm2 s) for the emission transitions of Dy3+ions doped OFSbB glasses
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Photoluminescence Decay Analysis

With an excitation wavelength of 351nm and an emission wavelength of 575nm, the time decay profile for all the as prepared samples that correspond to the 4F9/2 state was taken into consideration. As can be seen in Fig. 9, the time decay profile of each Dy3+ ions doped glass sample contained only one exponential and the estimated values for the decay time. Due to the concentration quenching effect, it was discovered that the time decay values decreased as Dy3+ ions concentration increased [50]. Using the following the expressions reported in the literature [41], the experimental lifetimes of the as prepared glasses are calculated by fitting the decay profiles by using following equation

$${{\text{I}}}_{{\text{t}}}={{\text{I}}}_{{\text{o}}}{{\text{e}}}^{\frac{{\text{t}}}{{\uptau }_{{\text{exp}}}}}$$
(10)

where It and Io represent the intensities of emission for decay curves at t = 0 and t = t respectively. With an increase in the concentration of the Dy3+ ions, the experimental lifetime values of the 4F9/2 level are 140, 135, 115, 105, 95 and 84(µs) corresponding to OFSbB0.1, OFSbB0.5, OFSbB1.0, OFSbB1.5, OFSbB2.0, and OFSbB2.5, respectively. The determined radiative lifetimes are opposing more from the experimental lifetimes which is due to non-radiative transition in the glass. The quantum efficiency (η) is the ratio of number photons emitted to the photons observed. For RE ions doped glasses, the quantum efficiency is expressed as

Fig. 9
figure 9

The decay curves of Dy3+ ions doped OFSbB glass samples

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$$\upeta =\frac{{\uptau }_{{\text{exp}}}}{{\uptau }_{{\text{R}}}}\mathrm{ x }100$$
(11)

The η values are decrease with increase in Dy3+ ions concentration due to increase of non-radiative transition rates. These rates can be calculated by difference of inverses of experimental and radiative lifetime value:

$${{\text{W}}}_{{\text{NR}}}= \frac{1}{{\uptau }_{\mathrm{exp }}}- \frac{1}{{\uptau }_{{\text{rad}}}}$$
(12)

The determined values of the quantum efficiency and WNR are of prepared glasses are tabulated in the Table 6 and compared with reported values. The WNR values of OFSbBDy0.5 are minimum which is evidently the OFSbBDy0.5 possess higher stimulated emission cross section and quantum efficiency.

Table 6 Experimental lifetimes (τexp), radiative lifetimes (τR), quantum efficiency (η) and non-radiative decay rates (WNR) of 4F9/2 → 6H13/2 transition of OFSbBDy glasses along with reported other glasses.
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Commission Intermediate de I’ Elcairage (CIE) Chromaticity Coordinates.

The combination of two intense emissions (blue and yellow) in the visible region can generate white light, which was analyzed using the Commission Internationale de I'Eclairage (CIE) to obtain color coordinates. Slightly emission color is labeled using color identical function (X, Y, Z) besides the color of the spectral power density P(λ) must match the simulation for each of the three primary colors. The tristimulus values are used to calculate the chromaticity coordinates x and y using the equations.

$${\text{x}}=\frac{{\text{X}}}{({\text{X}}+{\text{Y}}+{\text{Z}})}\cdots ;\cdots =\frac{{\text{Y}}}{\left({\text{X}}+{\text{Y}}+{\text{Z}}\right)}\,{\mathrm{and}}\,{\mathrm{z}}=\,\frac{{\text{Z}}}{({\text{X}}+{\text{Y}}+{\text{Z}})}$$
(13)

As a result, the coordinates for white-light emission are close to the center of the chromaticity diagram. Plots of the CIE chromaticity diagram was made for each prepared glass sample in relation to various excitation wavelengths. Figures 10 and 11 depicts the CIE diagram for the OFSbBDy0.5 sample with various excitations, as well as the CIE diagram for all samples with an excitation wavelength of 351nm. In comparison to the other excitations, the OFSbBDy0.5 sample produce the significant near-white light emission for the 351nm excitation. The emission from Dy3+ ions-doped glasses as depicted by the corresponding CIE coordinates (x,y) in Table 7 which suggests their potential use as materials for w-LEDs applications.

Fig. 10
figure 10

CIE 1931 chromaticity diagram of Dy3+ ions doped OFSbB glass samples

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Fig. 11
figure 11

CIE profile for Dy series at different excitation wavelengths

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Table 7 CIE Chromaticity coordinates (X and Y) and Y/B ratios of Dy3+ ions doped OFSbB glasses excited at 351nm wavelength.
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McCamy proposed a third-order polynomial equation for calculating CCT from CIE 1931 color coordinates in order to examine the quality of any light source in terms of correlated color temperature. This equation reduces the specification of white color from two dimensions (CIE diagram) to one dimension [51].

$${\text{CCT}}= -49{{\text{n}}}^{2}+352{{\text{n}}}^{2}-682{\text{n}}+5520.33$$
(14)

The reciprocal slope is given by \({\text{n}}=({\text{x}}-{{\text{x}}}_{\mathrm{e }})/({\text{y}}-{{\text{y}}}_{{\text{e}}})\) and the convergence epicenter is given by xe = 0.332, ye = 0.186 respectively. In most cases, the CCT values can be used to identify white light. If CCT value ≤ 3700 K, it corresponds to emission which represent warm and the emission color is pure for CCT values between 3700 and 5000K, it is considered as pure and below 5000 K, it is considered cooler. Hence, it is noteworthy that the CCT values estimated in Tables 8 and 9 for the OFSbBDy0.5 sample excited at wavelength of 351nm were found to be pure white light.

Table 8 CIE Chromaticity coordinates (X and Y) and Y/B ratios of OFSbBDy0.5 glasses at different excitation wavelengths.
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Table 9 Comparison of CIE Chromaticity coordinates (X and Y) and Y/B ratios of OFSbBDy glasses with other reported Dy3+ doped glasses.
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Gamma Radiation Shielding Properties

Web-based software.

Photon shielding and dosimetry (PSD) software is a user-friendly online software program accessible on https://phy-x.net/PSD, which was established used for to calculate the parameters related to shielding and dosimetry. Depending on the number of calculations, it produces results on a NodeJS platform in a reasonable amount of time. The software generates data on radiation shielding parameters by selecting two energies that have been defined in the software namely 0.0015MeV-15MeV & 1keV to 100GeV. In addition, the software includes a number of well-known radioactive sources (22Na, 55Fe, 60Co, 109Cd, 131I, 133Ba, 137Cs, 152Eu, & 241Am), as well as their energies and some characteristic like K-shell X-ray energies for Rb, Mo, Ag, Cu, Ba & Tb elements, which the user can select. The parameters include the mass attenuation coefficient, linear attenuation coefficient, half-value layer, tenth value layer, effective atomic number, mean free path, effective conductivity, electron density, energy absorption, and exposure buildup factor.

Gamma Ray-radiation Shielding Parameters Fundamental Relations:

By following the Beer-Lambert’s law, reduces the intensity of the beam when a material with the thickness “x” is placed in the path of a monoenergetic x-ray and gamma ray beam.

$${\text{I}}={{\text{I}}}_{0}{{\text{e}}}^{-\mathrm{\mu x}}$$
(15)

where I0 and I are the intensities prior to and following attenuation, respectively; x is the thickness of the sample; and µ is the Linear Attenuation Coefficient cm−1 (LAC). LAC is important because it describes the material interaction with radiation and it quantifies how much radiation is absorbed/scattered as it passes through the material.

The mass attenuation coefficient (MAC) is an important parameter for calculating the radiation shielding parameters. Understanding behavior of radiation and developing new applications for radiation-based new technologies require the MAC. It is used to evaluate the probability of interaction of the photons with the glass sample. It is theoretically calculated by using mixture rule [52].

$${{\text{MAC}}}_{\left({\upmu }_{{\text{m}}}\right)}=\mu /\rho ={\Sigma }_{{\text{i}}}{{\text{w}}}_{{\text{i}}}{(\upmu /\uprho )}_{{\text{i}}}$$
(16)

Here, \({(\upmu /\uprho )}_{{\text{i}}}\) and \({{\text{w}}}_{{\text{i}}}\) are the photon mass attenuation coefficient and weight fraction of the element and the “i” is obtained from the aforementioned software.

The material’s thickness level in cm is referred to as the half-value layer (HVL). which can reduce the incoming radiation to half of its initial value [53, 54]. The low HVL value implies many interactions of gamma rays with the sample; thus, the prepared sample has better gamma ray shielding effectiveness. HVL is likewise to another parameter called the Mean Free Path (MFP), which characterizes the typical distance went by a photon in the medium before the interaction happens. The following equations can be used to determine the HVL and MFP:

$${\text{HVL}}=\frac{0.693}{\upmu }$$
(17)

and,

$$\mathrm{MFP }= \frac{1}{\upmu }$$
(18)

where, µ is the Linear Attenuation Coefficient “which is equal to the MAC x density of the prepared sample.”

The effective atomic number (Zeff) was used to calculate the shielding characteristics of the materials. Zeff can be calculated using the following equation [55, 56].

$${{\text{Z}}}_{{\text{eff}}}= \frac{{\upsigma }_{{\text{t}},{\text{a}}}}{{\upsigma }_{{\text{t}},{\text{el}}}}$$
(19)

Here,

$${\upsigma }_{{\text{t}},{\text{a}}}= \frac{\upmu /\uprho }{{{\text{N}}}_{{\text{A}}}{\Sigma }_{{\text{i}}}(\frac{{{\text{W}}}_{{\text{i}}}}{{{\text{A}}}_{{\text{i}}}})}\cdots ;\cdots {\upsigma }_{{\text{t}},{\text{el}}}\frac{1}{{{\text{N}}}_{{\text{A}}}}{\Sigma }_{{\text{i}}}\frac{{{\text{f}}}_{{\text{i}}}{{\text{A}}}_{{\text{i}}}}{{{\text{Z}}}_{{\text{i}}}}(\upmu /\uprho )$$

Where, Ai is atomic weight of the ith element, NA is Avogadro’s number, fi & Zi are fractional abundance & atomic number respectively of the ith element.

In high-energy radiation fields, where the radiation buildup can be significant, exposure buildup factor (EBF) plays crucial role. Also, the EBF is an essential parameter for estimating the distribution of photons in an illuminated medium [57]. The ability of the EBP is to predict the dose rate at a specific point behind a shield. The EBP was calculated using the following steps:

  1. (a)

    Finding the equivalent atomic number (Zeq)

  2. (b)

    Finding the G-P fitting parameters (b,c,a,Xk & d)

  3. (c)

    Finding the exposure buildup factor EBF.

Results

The gamma-ray shielding parameters of the prepared glasses were measured for incident photon energy 0.015-15MeV Figure 12. The variation of MAC, LAC, HVL, TVL and MFP of the prepared OFSbBDy glasses. The decrease with increasing photon energy is owing to attenuators deeper penetration of photons. The fact that the change of the MAC values seen that the swift decrease at the range of 0.02–0.5MeV is due to photoelectric absorption (PE) which becomes dominant process. After a slight decrease in the range of 0.5-3MeV MeV, Compton scattering (CS) becomes the dominant process. Subsequently, the minor increase in the photon energy range of 4-15MeV was due to the pair production process (PP). The linear attenuation coefficient of the prepared glasses, which has a higher value in the lower-energy region and a lower value in the higher-energy region. The LAC results in a trend similar to of that the MAC. Hence, OFSbBDy2.5 glass had a higher shielding effectiveness than the others.

Fig. 12
figure 12

The variation of mass attenuation coefficient, linear attenuation coefficient, half value layer, tenth value layer, Mean free path of the prepared OFSbBDy glasses

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The HVL in the lower region is the same for all the samples; thereafter, an increase in the value, peak is observed in the range of 0.02–0.5MeV for all glass samples. The TVL results which exhibits the same trend as the HVL. The MFP exhibits a behavior similar to that of the HVL and TVL, which are independent in the lower region (0.01MeV) and dependent in the higher region(15MeV). The Mean Free Path values for the prepared glass samples, ordinary concrete [58], and zinc oxide soda-lime silica glass [59] are compared in Fig. 13. This clearly indicates that the prepared glass samples possessed better shielding properties. Furthermore, the results of MAC and HVL at 1173keV are also compared to those of other radiation shielding concretes (ordinary glass, barite, chromite and Ferrite) in order to provide a more conclusive picture of studied glasses attenuation capacity and the results are shown in Fig. 14 the OFSbBDy2.5 glass has a lower value than concrete, indicating that OFSbBDy glasses are better protection form γ-radiation.

Fig. 13
figure 13

Mean Free Path for prepared glass in comparison with ordinary concrete and zinc oxide soda lime silica

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Fig. 14
figure 14

Comparison of Mass Attenuation Coefficient (MAC) (cm2/g) and Half Value Layer (HVL) (cm) at 1173 keV of 2.5 mol% doped OFSbB glass with different concretes

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For all prepared glass samples, the high Zeff value is observed in low region and decreased with increases photon energy. Zeff increases with increase in Dy2O3 content and it results that OFSbBDy2.5 can absorb high photon energy. Figure 15 shows the variation of the effective atomic number (Zeff) with the photon energy for the OFSbBDy glasses. From the Fig. 15 we can observe that high Zeff was observed at 0.04MeV, where the photoelectric effect and predominant scattering is Compton. The interaction of cross-section, which is directly proportional to the atomic(Z) number, is the Compton scattering process. Consequently, it explains the change of the value in the lower region of Zeff. However, Zeff reaches its minimum value in the range of 1MeV to 5MeV. Finally, it remains constant after increase in photon energy hence the prepared glasses are competent shielding materials.

Fig. 15
figure 15

The variation of the effective atomic number (Zeff) with the photon energy for the OFSbBDy glasses

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Figure 16 represents the variation of the Exposure build factor with the photon energy for the OFSbBDy glasses. Figure 17 shows the EBF values in the lower range (0.015–0.3MeV) are most unity for different penetration depths. As we observed that the sharp peak in the EBF values which can be attributed of k-edge absorption of the glass continents. The graph makes it abundantly clear that the prepared glasses' EBF increase with the mean free path. This also results increase of scattering events in target medium. Hence it results in large EBF values.

Fig. 16
figure 16

The variation of the Exposure build factor with the photon energy for the OFSbBDy glasses

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Fig. 17
figure 17

The variation of the Exposure build factor with the photon energy for the OFSbBDy glasses

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Conclusion

A series of Dy3+ ions doped antimony-oxyfluoro-borate glasses with a composition of 60B2O3-10Sb2O3-10Al2O3-10NaF-(10-x) LiF-xDy2O3(x = 0.1,0.5,1.0,1.5,2.0,2.5mol%) were prepared by using the conventional melt quenching method in this study. Various characterization methods, including UV–Vis-NIR, FTIR, luminescence, time decay. The non-metallic nature of NBO and glasses is the result of significant changes in a number of physical parameters brought about by the incorporation of Dy3+ ions into the host. UV–Vis-NIR absorption spectra also reveals the other host-dependent transitions and an intense peak that is associated with a hypersensitive transition. The Judd–Ofelt theoretical calculations were used to determine the radiative parameters and efficiency. From the J-O analysis, it was found that the J-O parameters follow the order(Ω2 > Ω6 > Ω4). The optical bandgap analysis was estimated using Tauc’s method. Emission studies have been analyzed using the excitation wavelengths from 351 to 575nm. The glass containing 0.5mol% of Dy3+ ions produced intense light-like emission when excited at 351nm wavelength. In general, Dy3+ ions incorporated antimony-oxyfluoroborate glasses are potential candidates for white light emission applications. The radiation shielding parameters of the prepared OFSbBDy glasses were studied at various photon energies (0.015MeV-15MeV) using PSD software. The MAC, LAC, HVL, TVL, MFP of the prepared glasses results same trend. The prepared glass OFSbBDy2.5 sample is capable of better radiation absorption glasses than the ordinary concrete and some other glass systems. Hence the prepared glass samples are good for shielding materials as well as optical applications.