Enhanced Emission Properties of Dysprosium Ions Doped Lead Borophosphate Zinc Barium Glasses for White Light Luminescent Applications

Abstract

Lead borophosphate zinc barium glass systems doped with different concentrations of Dy₂O₃ (0.5–2.0 mol%) were fabricated using the traditional melt-quenching method. The non-crystalline nature of the synthesized glass samples was verified through X-ray diffraction (XRD) analysis, which exhibited the characteristic absence of sharp diffraction peaks. Morphological, structural, and vibrational properties were analyzed using scanning electron microscopy (SEM) and Fourier infrared transmission (FTIR) spectroscopy. Optical absorption, emission, and decay lifetime observations were recorded to evaluate the luminescence behavior of Dy³⁺ ions. Judd–Ofelt parameters (Ω₂, Ω₄, and Ω₆) were evaluated from the optical absorption spectra of all the prepared glass samples. The emission spectra revealed three dominant transitions in the visible region corresponding to the ⁴F_9/2 ⟶ ⁶H_15/2 (blue ~ 484 nm), ⁴F_9/2 ⟶ ⁶H_13/2 (yellow ~ 574 nm), and ⁴F_9/2 ⟶ ⁶H_11/2 (~663 nm) transitions. Radiative characteristics, including radiative transition probability (A_R), radiative lifetime (τ_R), and branching ratio (β_R), were calculated from the emission spectra. Among the investigated compositions, the host glass embedded with 1.0 mol% Dy₂O₃ demonstrated the maximum emission intensity was observed along with superior quantum efficiency (η = 91.68%). The chromaticity coordinates for this composition (x = 0.33, y = 0.41) are positioned close to the white-light region in the CIE 1931 chromaticity diagram. These findings suggest that incorporating 1.0 mol% of Dy₂O₃ yields the highest luminescence efficiency, making the present glass system a promising candidate for white-light-emitting and photonic device applications.

1. Introduction

Glasses incorporating dysprosium oxide (Dy₂O₃) are commonly utilized as white-light-emitting materials due to their distinctive emission transitions, which are well recognized. Especially, these glasses exhibit blue and yellow emission transitions, viz., ⁴F_9/2 → ⁶H_15/2 (electronic dipole) and ⁴F_9/2 → ⁶H_13/2 (magnetic dipole). The emission intensity ratio (Y/B) is different for different materials and significantly influences white-light generation. Moreover, Dy³⁺ ions exhibit emission bands at about 3.02 μm (⁶H_13/2 → ⁶H_15/2) and 1.34 μm (⁶H_11/2 → ⁶H_13/2) for optical fiber amplifier applications [1,2,3,4,5,6].

Dysprosium (Dy³⁺)-doped glasses have garnered significant attention due to their versatile luminescent properties arising from characteristic ⁴F_9/2 → ⁶H_15/2 (blue, ~480 nm) and ⁴F_9/2 → ⁶H_13/2 (yellow, ~570 nm) transitions, enabling white-light emission when these bands are balanced appropriately. This makes Dy³⁺-activated materials promising for solid-state lighting and display technologies. However, their utility spans beyond this, into fields like optical amplifiers, sensors, and radiation shielding, depending on the glass host and co-dopants used [7].

Compared to other rare earth ions such as Er³⁺, Nd³⁺, and Yb³⁺, which are predominantly used in optical amplifiers and telecommunication devices, and Eu³⁺ and Tb³⁺ ions, which exhibit red and green emissions suitable for display technologies, Dy³⁺ ions doped glasses are relatively less explored in commercial applications. However, Dy³⁺ ions offer distinctive advantages through their simultaneous emission (blue) ⁴F_9/2 → ⁶H_15/2 and (yellow) ⁴F_9/2 → ⁶H_13/2, respectively, enabling near-white-light generation from a single activator. Furthermore, Dy³⁺-activated glass possesses superior chemical stability, lower fabrication cost, and easier processability compared to conventional YAG: Ce phosphors. The strong sensitivity of Dy³⁺ emissions to local field symmetry and temperature also makes these materials promising candidates for optical thermometry and pressure sensing applications.

For these reasons, the current Dy³⁺ ions doped glass system is not merely an extension of known applications but an attempt to converge multiple functionalities of white-light generation, shielding, and optical sensing into a single platform. While other rare-earth systems may outperform Dy³⁺ ions in specialized roles, this ion offers a unique combination of optical characteristics and structural adaptability, especially in low-phonon glass hosts like PBPZBa. This broader perspective situates the study in the context of multifunctional rare-earth-doped materials, and the manuscript can benefit from including such a review to justify the material choice.

The luminescent behavior of rare earth Dy³⁺ ions doped lead borophosphate zinc barium glasses in the UV, visible, and NIR spectral regions. These glass materials are particularly applicable for applications in the white-light-emitting diodes, optical amplifiers, fiber optics, radiation shielding, and optical sensing. The presence of P₂O₅ and B₂O₃ promotes the formation of linkages B-O-P between PO₄ and BO₄ structural units. Such linkages contribute to a more interconnected glass network [8,9]. Incorporating lead oxide (Pb₃O₄) enhances the physical attributes like density and refractive index, and improves resistance to devitrification, as well as moisture degradation. Incorporating BaO and ZnO is essential for optimizing luminescence performance, structural robustness, and strong resistance to thermal degradation, which makes them promising candidates for advanced optical, photonic, and radiation shielding applications as mentioned [10,11].

In recent years, significant efforts have been devoted to understanding the incorporation mechanism and photoluminescence behavior of Dy³⁺ ions in various amorphous glass matrices, particularly borophosphate, borosilicate, tellurite, and lead-phosphate systems. Previous studies have demonstrated that the local structural environment, site symmetry, and covalency around Dy³⁺ ions strongly influence the intensity ratio of the ⁴F_9/2 → ⁶H_15/2 (blue) and ⁴F_9/2 → ⁶H_13/2 (yellow) transitions, which governs white-light generation. Judd–Ofelt analysis has been widely employed to evaluate the radiative properties and to correlate Ω₂ values with structural asymmetry in rare-earth-doped glasses. Furthermore, concentration quenching, cross-relaxation, and energy migration processes have been identified as key factors limiting emission efficiency at higher dopant levels. In multicomponent glass systems, network formers such as B₂O₃ and P₂O₅ and modifiers like PbO, ZnO, and BaO play a crucial role in tailoring the phonon energy, non-bridging oxygen content, and local crystal field strength, thereby directly affecting Dy³⁺ luminescence performance. Therefore, a systematic investigation of Dy³⁺ incorporation in Pb–B–P–Zn–Ba-based amorphous matrices is essential for optimizing white-light emission and enhancing photonic device applicability.

The present study investigates the impact of varying Dy³⁺ ion concentrations (0.5, 1.0, 1.5, and 2.0 mol%) in PbO-B₂O₃-P₂O₅-ZnO-BaO glasses on white-light luminescence. Among these, Dy10 glass exhibits the maximum luminescence intensity compared to other concentrations of Dy³⁺-doped glasses. This enhanced luminescence is attributed to lower non-radiative losses in the glass matrix. To better understand, the structural morphological investigations were carried out through X-ray diffraction, SEM, and FTIR studies.

2. Experimental

The detailed glass sample composition in the present study is as follows:

PBPZBaDy₅: 10PbO-20B₂O₃-49.5 P₂O₅-10ZnO-10BaO-0.5 Dy₂O₃;

PBPZBaDy₁₀: 10PbO-20B₂O₃-49.0 P₂O₅-10ZnO-10BaO-1.0 Dy₂O₃;

PBPZBaDy₁₅: 10PbO-20B₂O₃- 48.5 P₂O₅-10ZnO-10BaO-1.5 Dy₂O₃;

PBPZBaDy₂₀: 10PbO-20B₂O₃-48.0 P₂O₅-10ZnO-10BaO-2.0 Dy₂O₃.

High-purity chemical reagents, including PbO, H₃BO₃, P₂O₅, ZnO, BaCO₃, and Dy₂O₃, were weighed with precision and uniformly blended with an agate mortar. The uniform powder mixture was melted in a silica crucible at 1350 °C for one hour using a PID-controlled furnace. After obtaining a homogeneous melt, the liquid was poured into a preheated brass mold and subjected to annealing at 450 °C to relieve residual internal stresses within the prepared samples. Synthesized glass samples exhibited an amorphous nature, which was verified through XRD analysis carried out using a Rigaku D/Max ULTIMA III diffractometer (Rigaku Corporation, Tokyo, Japan) utilizing CuKα radiation. The prepared glass samples were optically polished to dimensions of approximately 1.0 × 0.2 cm², and their densities were measured using Archimedes’ principle with o-xylene employed as the liquid medium. Refractive index values were calculated using an Abbe refractometer with mono-bromonaphthalene as the contact medium, utilizing a sodium light source (589.3 nm wavelength). Optical absorption spectra of the fabricated samples were recorded at room temperature over the wavelength range 200–1800 nm using a UV-Vis-NIR spectrophotometer (JASCO Corporation, Tokyo, Japan). Emission spectra for all the glasses were obtained at room temperature using a (Lumina) Thermo Scientific luminescence spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA) operating within a wavelength range of 200 to 900 nm. The lifetime decay measurements are performed following methodologies outlined in previous studies [12,13].

In the present glass compositions, Dy₂O₃ was incorporated by partially substituting P₂O₅ while maintaining the total molar percentage at 100 mol%. P₂O₅ acts as a primary glass former in the borophosphate network; therefore, its gradual reduction compensates for the introduction of Dy³⁺ ions without significantly disturbing the overall glass-forming ability. The substitution strategy ensures compositional consistency across all samples and enables a systematic investigation of the influence of Dy³⁺ concentration on structural and luminescence properties. The incorporation of Dy³⁺ ions in place of P₂O₅ is expected to modify the local network connectivity by generating non-bridging oxygens (NBOs) and altering the P–O–P and B–O–P linkages, which in turn affects the optical and radiative characteristics of the prepared glasses.

3. Results and Discussion

Physical properties of the prepared glass samples with different Dy³⁺ ion concentrations were evaluated using established formulas [14,15], measured molecular weight (M), density ($\mathrm{\rho }$), refractive index (n_d), and the experimentally determined parameters. The related physical properties were summarized in

Table 1. Physical parameters of Dy³⁺ ions doped PbO-B₂O₃-P₂O₅-ZnO-BaO glasses.

Glass Sample	Avg. Mo. Wt. M	Density d (g/cm3)	Dy3+ Ion Conc. Ni (1019/cm3)	Inter Ionic Distance of Dy3+ Ions Ri (nm)	Refractive Index, nd	Optical Band Gap (Eo)
PBPZBaDy5	248.37	3.75	4.55	2.80	1.613	3.78
PBPZBaDy10	248.82	3.82	9.15	2.21	1.635	3.73
PBPZBaDy15	249.27	3.81	1.38	1.93	1.619	3.85
PBPZBaDy20	249.71	3.80	1.85	1.75	1.626	3.88

.

The density of each glass sample was determined based on Archimedes principle using o-xylene as the immersing liquid, following the relationship [13,16]:

$$\mathrm{\rho }(\mathrm{gm}/{\mathrm{cm}}^3) = \left[{\displaystyle \frac{\mathrm{W}\mathrm{a}}{\mathrm{W}\mathrm{a}-\mathrm{W}\mathrm{b}}}\right]\times {\mathrm{\rho }}_{\mathrm{b}}$$

(1)

the weight of the glass sample in air is denoted by W_a, while W_b represents the weight of the glass sample when submerged in o-xylene. The density of o-xylene is given as ρ_b = 0.86 g/cm³. The molar volume (V_m) of the glass samples was determined using the following formula:

$${\mathrm{V}}_{\mathrm{m}} = \mathrm{MT}/\mathrm{\rho }$$

(2)

Here $\mathrm{\rho }$ represents the density of the samples, and MT denotes the total molecular weight of the multi-component of the glass system, determined using the following relation:

MT = XPbO + XB₂O₃ + XP₂O₅ + XZnO + XBaO

(3)

where X is molar fraction of the chemical component.

The refractive index (n_d) of the samples was determined directly using an Abbe refractometer.

Figure 1 illustrates variation in density ($\mathrm{\rho }$) and refractive index (n_d) as a function of Dy³⁺ ion concentration. The results indicate that increasing Dy³⁺ from 0.5 to 1.0 mol% enhances both density and refractive index. At lower Dy₂O₃ concentrations (0.5–1.0 mol%), the high field strength and relatively large atomic mass of Dy³⁺ enhance Dy–O bond strength and improve local structural compactness without significantly disrupting the glass network. The FTIR spectra support this interpretation. For the 1.0 mol% sample, the bands corresponding to asymmetric P–O–P and B–O–P linkages (around ~1080–910 cm⁻¹) show relative strengthening, indicating improved cross-linking between BO₄ and PO₄ units and reduced structural disorder. This enhanced network connectivity and compact packing explain the observed increase in density (3.75 → 3.82 g/cm³) and refractive index (1.613 → 1.635).

However, beyond 1.0 mol% Dy₂O₃, excessive incorporation of Dy³⁺ leads to the formation of additional non-bridging oxygens (NBOs) and partial disruption of P–O–P/B–O–P linkages, as indicated by the relative enhancement of bands associated with PO₂⁻ and BO₃ units in the FTIR spectra. Furthermore, possible Dy³⁺-Dy³⁺ clustering at higher concentrations reduces network connectivity and structural compactness. This increased depolymerization explains the slight decrease in density and refractive index for 1.5 and 2.0 mol% samples. Thus, the non-linear trend reflects an initial network strengthening effect followed by depolymerization and ion clustering at higher Dy³⁺ content.

Figure 2 presents the X-ray diffractogram pattern for all the glass samples, confirming their amorphous structure within the glasses. Figure 3 shows the SEM image of PBPZBaDy₁₀ glass, revealing microscale surface features. These grain formations likely originated during the melting and annealing stages.

Figure 4 shows the FTIR spectra of PBPZBaDy₁₀ glass, which exhibits distinct vibrational bands corresponding to different structural units present in the borophosphate glass network. The bands observed at ~1280 cm⁻¹ and 1240 cm⁻¹ are associated with trigonal BO₃ and P=O bonds of PO₂⁻ stretching vibrations, respectively. These high-frequency bands arise from strong B-O and P=O bonds present in the network. The peak around 1080 cm⁻¹ corresponds to the symmetric stretching vibrations of tetrahedral BO₄⁻ and PO₄³⁻ units. Another band near 910 cm⁻¹ is assigned to asymmetric stretching vibrations of bridging P–O–P linkages, confirming the formation of a connected phosphate network. Additional bands at 780 cm⁻¹ and 690 cm⁻¹ indicate symmetric P–O–P and B–O–B band vibrations, which further support the presence of a mixed borophosphate structural framework. The low-frequency band around 500 cm⁻¹ is attributed to Pb-O and Zn-O vibrations, indicating the participation of PbO₄ and ZnO₄ structural units acting as network modifiers. All the assigned bands are tabulated in

Table 2. Characteristic FTIR vibrational bands and their assignments for structural units in borophosphate glass systems.

Observed Region (cm−1)	Assignment
~1280–1240	BO3/P=O and PO2− Stretching
~1080	BO4− and PO43− symmetric stretching
~910	Asymmetric P–O–P vibrations
~780	Symmetric P–O–P stretching
~690	B–O–B linkages
~500	PbO4/ZnO4 structural units

. Notably, the asymmetric vibration bands of the highest intensity and slightly broadened in 1.0 mol% of Dy³⁺-doped glasses suggest increased network disruption [17,18,19,20,21].

Figure 5a,b presents the absorption spectra of the labeled glass samples measured over a 200–2000 nm range. The spectra have exhibited the bands in the UV-vis-NIR region corresponding to 4f electron transitions of Dy³⁺ ions: ⁶H_{15/2 →} ⁴G_11/2 + ⁴M_21/2, ⁴I_15/2, ⁴F_9/2, ⁴G_9/2 + ⁴I_11/2, ⁶F_1/2, _3/2, _5/2, _7/2 (UV-vis region), and ⁶F_9/2, ⁶F_11/2+⁶H_9/2, and ⁶H_11/2 (NIR region). Among these, the transitions ⁶H_{15/2 →} ⁴G_11/2 + ⁴M_21/2,⁶F_1/2 (vis), and ⁶F_11/2 NIR region exhibit greater intensity than other transitions.

In the visible–NIR region, several weaker Dy³⁺ absorption features accompany the dominant bands. A shoulder between 570 and 600 nm is assigned to the ⁶H_15/2 → ⁴G_9/2 transition, with possible contribution from nearby ⁴I_11/2. In the 760–795 nm range, the spectral structure results from overlapping ⁶H_15/2 → ⁶F_3/2 (≈760–780 nm) and ⁶H_15/2 → ⁶F_5/2 (≈790–800 nm) transitions, whose Stark components are partially resolved in the glass host. Additional weak bands observed between 1400 and 1600 nm are attributed to higher Stark levels within the ⁶F_9/2–⁶H_7/2 group, and their evolution with Dy³⁺ content reflects changes in the local crystal field rather than any sample-mixing artifact.

The slight variation in the absorption profile observed at different Dy³⁺ concentrations is attributed to concentration-induced modifications in the local field environment and Stark splitting effects within the glass network. These systematic spectral changes correlate well with the trends observed in density, refractive index, Judd–Ofelt parameters, and lifetime measurements, confirming that the variations arise from structural effects rather than any sample misidentification.

The decrease in peak intensities of absorption spectra, with increasing Dy³⁺ ion content more than 1.0 mol% in PbO-B₂O₃-P₂O₅-ZnO-BaO glasses, can be attributed to concentration quenching effects. At lower Dy³⁺ concentrations (1.0 mol%), the ions are uniformly distributed within the glass network, enabling effective optical absorption, whereas higher concentrations (1.5 and 2.0 mol%) promote stronger Dy³⁺–Dy³⁺ interactions that facilitate non-radiative energy transfer through cross-relaxation and energy migration processes, leading to reduced absorption intensity and total optical conversion efficiency.

The optical energy gap (E₀) is a key parameter for understanding the electronic structure and optical response of glass materials. In this study, E₀ values for Dy³⁺-doped samples were determined from the UV–Visible absorption spectra using Tauc’s method (Figure 6). The extracted band gap primarily corresponds to the fundamental absorption edge of the host glass matrix arising from charge-transfer transitions between oxygen ions and network-forming cations. The Dy³⁺, 4f–4f transitions appear as weak and sharp bands superimposed on the broad absorption edge and, owing to their localized and parity-forbidden character, do not affect the linear region used for band gap extrapolation. Hence, the evaluated E₀ values mainly reflect changes in the glass network structure rather than direct contributions from Dy³⁺ electronic transitions. With Dy³⁺ incorporation up to 1.0 mol%, a slight decrease in E₀ is observed, which is attributed to the generation of additional non-bridging oxygens and increased structural disorder. The variation in E₀ values indicates compositional modification of the glass network and confirms the suitability of the material for photonic and luminescent device applications [22,23].

The absorption coefficient α is correlated with the optical band gap energy (E_o), which can be expressed using the following relation:

α (hν) ∝ B (hν − E_opt)^1/2

(4)

Here, B corresponds to the band tailing parameter, while hν represents the photonic energy. The value of E₀ was observed for 1.0 mol% of Dy³⁺-doped glass composition (Table 1), suggesting an increased level of structural disorder within the glass network.

The experimental oscillator strengths (OS) (f_exp) corresponding to various absorption transitions of Dy³⁺ ions in PBPZBa glasses were evaluated from the absorption spectra using the standard equation [23].

$$f_{exp}=4.319\times 10^{-9}\ast \int \epsilon \left(\nu \right)d\nu$$

(5)

The parameters involved in Equation (2) are defined in earlier reports [24,25,26,27,28].

The calculated electric dipole oscillator strengths (f_cal) for Dy³⁺ ions were obtained using Judd–Ofelt theory, as described in Equation (6), following the formulations reported in Refs. [24,25,26,27,28]. A close agreement between f_exp and f_cal values was observed, as evidenced by the root mean square deviation presented in

Table 3. The absorption band energies and the oscillator strengths (f ×10⁻⁶) for the transitions of Dy³⁺ ions in PbO-B₂O₃-P₂O₅-ZnO-BaO glasses.

Glass	PBPZBaDy5			PBPZBaDy10			PBPZBaDy15			PBPZBaDy20
Transition 6H15/2⟶	Barycenter (cm−1)	fexp (×10−6)	fcal (×10−6)	Barycenter (cm−1)	fexp (×10−6)	fcal (×10−6)	Barycenter (cm−1)	fexp (×10−6)	fcal (×10−6)	Barycenter (cm−1)	fexp (×10−6)	fcal (×10−6)
6H11/2	5988	0.051	0.056	5989	0.069	0.054	5990	0.052	0.051	5990	0.053	0.051
6F11/2	7812	0.232	0.216	7815	0.281	0.246	7817	0.241	0.257	7820	0.251	0.257
6F9/2	9095	0.164	0.118	9099	0.163	0.151	9102	0.161	0.167	9100	0.171	0.171
6F7/2	12,165	0.236	0.230	12,173	0.236	0.242	12,177	0.223	0.239	12,180	0.233	0.237
6F5/2	12,484	0.387	0.361	12,475	0.467	0.468	12,479	0.354	0.361	12,481	0.344	0.361
6F3/2	13,333	0.186	0.181	13,324	0.262	0.212	13,329	0.185	0.191	13,330	0.186	0.193
6F1/2	14,619	0.633	0.637	14,630	0.732	0.724	14,637	0.641	0.644	14,640	0.643	0.644
4F9/2	18,796	0.149	0.135	18,811	0.161	0.169	18,825	0.151	0.150	18,828	0.142	0.153
4I15/2	22,050	0.419	0.437	22,075	0.549	0.546	22,075	0.424	0.437	22,079	0.414	0.427
4G11/2	23,419	0.305	0.271	23,446	0.366	0.391	23,463	0.310	0.328	23,465	0.317	0.321
δrms (×10−6)			±0.31			±0.46			±0.33			±0.30

.

$$f_{\mathrm{cal}}={\displaystyle \frac{{8\pi }^{2}mcv\chi }{3h(2J+1)}}{\sum }_{\lambda =\mathrm{2,4},6}{\Omega }_{\lambda }{〈f^N\left[\gamma ,S, L\right]J‖U^{\lambda }‖f^N\left[{\gamma }^{\prime },S^{\prime },L^{\prime }\right]J^{\prime }〉}^2$$

(6)

Using Equation (6), the J-O parameters (Ω₂, Ω_{6, and} Ω₄) were determined for all the Dy³⁺-doped glass samples. The evaluated parameters follow the trend Ω₂ > Ω₆ > Ω₄ (Table 3), which is consistent with earlier reports [29,30,31]. Among the studied samples, the glass PBPZBaDy₁₀ exhibited the lowest Ω₂ value, suggesting reduced asymmetry and lower covalency around Dy³⁺ ions. Notably, the Ω₂ value decreases progressively with Dy³⁺ ion concentration increased up to 1.0 mol%, beyond which an increase is observed for higher dopant levels (1.5 and 2.0 mol%).

This behavior indicates an initial reduction in the covalent character of the Dy-O bonds, followed by increased structural distortion at higher concentrations. The increase in Dy³⁺ content likely perturbs the glass network by enlarging the spacing between P–O–P and B–O–P linkages. Accordingly, the Dy–O bond lengths increase, leading to a weakened local crystal field around Dy³⁺ ions. This structural modification helps suppress phonon-assisted losses and cross-relaxation processes, thereby improving the optical performance of the glass system.

Figure 7 indicated emission spectra (λ_exc = 348 nm) for all the glass samples have their origin from excited level ⁴F_9/2 and exhibited the emission bands from ⁴F_9/2 to ⁶H_15/2 (blue ~ 484 nm), ⁶H_13/2 (yellow ~ 574 nm), and ⁶H_11/2 (red ~ 663 nm) correspondingly. Out of these, yellow emission (~574 nm) is usually most intense, leading to a white-light emission when balanced with blue emission. The emission intensity Y/B ratio values (for 0.5 mol% = 1.187, for 1.0 mol% = 1.185, for 1.5 mol% = 1.184, and for 2.0 mol% = 1.188) depend on factors such as Dy³⁺ content of the glass composition. The transition ⁴F_9/2 → ⁶H_13/2 (ΔL = 2, ΔJ = 2) is observed to be hypersensitive. As the content of Dy₂O₃ increases, a significant enhancement in the intensity of the band (⁴F_9/2 → ⁶H_13/2) is observed. However, beyond 1.0 mol%, the emission quenching occurs. Figure 8 illustrates the energy level diagram depicting different absorption and emission transitions associated with Dy³⁺ ions in the PBPZBaDy₁₀ glass sample.

The emission transition probabilities associated with electric dipole transitions were evaluated using the relation:

$$A_{J{J}^{\prime }}={\displaystyle \frac{64{\pi }^4{e}^2{v}^3}{3h (2J+1)}}{\displaystyle \frac{{n (n^2+2)}^2}{9}}{\sum }_{\lambda =\mathrm{2,4},6}{\Omega }_{\lambda }{〈f^N\left[\gamma ,S, L\right]J‖U^{\lambda }‖f^N\left[{\gamma }^{\prime },S^{\prime },L^{\prime }\right]J^{\prime }〉}^2$$

(7)

The detailed explanation of the above equation can be found in the referenced literature [7,25,28].

From the emission spectra, radiative parameters including the spontaneous emission probability (A), total radiative transition probability (A_T), radiative lifetime (τ), and fluorescence branching ratio (β) corresponding to the transitions originating from the ⁴F_9/2 excited state of Dy³⁺ ions were evaluated using conventional Equations (8)–(10) and were presented in

Table 4. J-O parameters (Ω_λ × 10⁻²⁰, cm⁻²) of Dy³⁺ ions doped in Pb₃O₄-B₂O₃-P₂O₅-ZnO-BaO glasses.

Glass Sample	PBPZBaDy10
Transition 4F9/2 ↓	Bary-center (cm−1)	A (s−1)	β (%)	σPE (×10−22, cm2)
⟶6H15/2	20,655	229	12.12	0.913
⟶6H13/2	17,422	1547	81.89	2.642
⟶6H11/2	15,140	113	5.98	0.655
		AT = 1889 s−1		τrad = 0.529 ms

for PBPZBaDy10 glass.

$$\mathsf{\tau }={\displaystyle \frac{1}{\sum _{J^{\prime }}{A}_{{JJ}^{\prime }}}}$$

(8)

$${\mathrm{\beta }}_{{JJ}^{\prime }}={\displaystyle \frac{A_{{JJ}^{\prime }}}{\sum _{J^{\prime }}{A}_{{JJ}^{\prime }}}}$$

(9)

$$\sigma \left(\lambda \right)={{\displaystyle \frac{{\lambda }^4{A}_{J{J}^{\prime }}}{8\pi c{n}^2\mathrm{\Delta }\lambda }}}_{eff}$$

(10)

The details of the above equations (Equations (8)–(10)) were explained in Refs [28,29,30].

We have observed the radiative parameters for PBPZBaDy10 glass tabulated in

Table 5. Various radiative properties of transitions of 1.0 mol% Dy³⁺ ions in PbO-B₂O₃-P₂O₅-ZnO-BaO glass.

Glass Sample	Ω2	Ω4	Ω6	Trend
PBPZBaDy5	9.13	2.74	3.05	Ω2 > Ω6 > Ω4
PBPZBaDy10	4.62	0.97	2.15	Ω2 > Ω6 > Ω4
PBPZBaDY15	5.60	1.44	3.11	Ω2 > Ω6 > Ω4
PBPZBaDy20	6.35	2.76	3.74	Ω2 > Ω6 > Ω4
PbPKANDy10 [29]	11.74	2.64	2.86	Ω2 > Ω6 > Ω4
TWZDy10 [30]	6.910	0.990	1.010	Ω2 > Ω6 > Ω4
BLND [31]	11.99	3.92	3.94	Ω2 > Ω6 > Ω4

, attributing the highest radiative values. This enhancement is attributed to the optimal distribution of Dy³⁺ ions at a doping concentration of 1.0 mol%, which promotes radiative transitions by effectively suppressing non-radiative losses. However, at higher Dy³⁺ contents (1.5 to 2.0 mol%), increased ion-ion interactions, cross-relaxation mechanisms, and energy transfer between adjacent Dy³⁺ ions result in concentration quenching effects. These processes diminish the radiative efficiency, leading to reduced fluorescence lifetimes and lower branching ratio values. Consequently, Dy³⁺ mixed 1.0 mol% is identified as optimal for achieving efficient luminescence with superior radiative properties in the present glass system.

Figure 9 shows the decay profile of PBPZBaDy10 glass from the ⁴F_9/2 level; corresponding lifetime values are listed in

Table 6. The experimental (τ_exp, μs) and calculated (τ_R, μs) life times and quantum efficiency (η, %) of Dy³⁺ ions doped in PbO-B₂O₃-P₂O₅-ZnO-BaO glasses.

Glass Sample	Measured (τexpμs)	Calculated (τR,μs)	Quantum Efficiency (η%)
PBPZBaDy5	361	437	82.61
PBPZBaDy10	485	529	91.68
PBPZBaDy15	438	496	88.30
PBPZBaDy20	382	441	86.66

. A comparatively longer radiative lifetime is observed in the glass doped with 1.0 mol%, suggesting a more covalent bonding environment around the Dy³⁺ ions, along with higher vibrational frequencies. The glass PBPZBaDy10 exhibits the highest quantum efficiency (η = 91.68), which enhances the yellow–blue (Y/B) luminescence, bringing it closer to the white-light region compared to other glasses.

The obtained quantum efficiency is comparable to or slightly higher than many previously reported Dy³⁺-doped phosphate, borate, and tellurite glasses, where efficiencies typically fall in the range of ~75–90%, depending on host matrix and dopant concentration. This confirms that the present PbO–B₂O₃–P₂O₅–ZnO–BaO glass system provides an efficient radiative environment for Dy3+ ion emission.

Figure 10 shows that chromaticity coordinates (x = 0.33, y = 0.41) lie in proximity to the white-light region of the CIE 1931 chromaticity diagram. As the Dy³⁺ ion concentration increases beyond 1.0 mol%, a gradual shift in the emission color toward the yellowish region is observed. Therefore, the 1.0 mol% Dy³⁺ composition provides an optimal balance between blue and yellow emissions, resulting in high quantum efficiency and chromaticity coordinates close to the ideal white-light region, comparable to other similar Dy³⁺-doped glass systems reported in the literature [7,29,30,31].

4. Conclusions

The present investigation demonstrates that Dy³⁺ ions doped PbO-B₂O₃-P₂O₅-ZnO-BaO glasses exhibited the remarkable luminescent behavior, with the sample containing 1.0 mol% Dy₂O₃ (PBPZBaDy10) showing superior optical performance. This composition achieved the highest luminescence intensity, radiative transition probabilities, and quantum efficiency (η = 91.68%). The emission spectra revealed two strong bands corresponding to the ⁴F_9/2 → ⁶H_15/2 (blue) and ⁴F_9/2 → ⁶H_13/2 (yellow) transitions, whose balanced intensities produced near-white light with chromaticity coordinates (x = 0.33, y = 0.41) in the CIE 1931 color space. Judd–Ofelt analysis exhibited the parameter trend Ω₂ > Ω₆ > Ω₄, indicating an asymmetric and moderately covalent environment around Dy³⁺ ions. Concentration quenching beyond 1.0 mol% was primarily due to Dy³⁺–Dy³⁺ cross-relaxation and non-radiative energy transfer processes. The novelty of this work lies in developing a multicomponent Pb–B–P–Zn–Ba glass matrix that simultaneously provides high optical transparency, chemical stability, and efficient single-ion white-light emission without co-dopants. These findings establish the glass PBPZBaDy10 as a promising material for next-generation white-light-emitting diodes (WLEDs), optical sensors, and photonic device applications.