Enhancement of Optical Telecommunication Bands: Pr3+-Doped Halide Phosphate Glasses Display Broadband NIR Photoluminescence Emission.

In the optical energy gap, visible and near-IR emission of halide phosphate glasses with a composition of 40P2O5-30ZnO-20LiCl-10BaF2 in mol% doped with 3.5 × 104 ppm Pr2O3, referred to as PZLBPr, were synthesized. The UV-VIS-NIR and spectroscopic properties of these glasses were also predicted. The current glasses had broadband emission photoluminescence covering a wavelength range of 1250 to 1700 nm when excited at 455 nm. These bands for near-infrared emission luminescence relate to the transitions 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3, 3F4 in the optical telecommunication window. The significant PL emission wideband was caused by the radiative transition from Pr3+: 1D2 to 1G4. At 445 nm excitation, these glasses exhibited emission bands that corresponded to blue/reddish orange spectral ranges in visible ranges. The prepared glass has a high lasing quality factor (Ω4/Ω6 = 0.9), high optical energy (4.72 eV), and quantum efficiency = 87.3% with FWHM = 156 nm of transition emission from the 1D2 → 1G4 level. As a result, broadband near infrared optical amplifiers can be fabricated from the prepared glasses.

1. Introduction

The C-, S-, E-, and O bands may be enhanced with the use of rare earth RE ions including Er3+, Tm3+, and Ho3+ [1,2,3,4,5]. It has been investigated whether the co-doped RE ions may improve population inversion and increase bandwidth [2,3] to avoid a number of undesirable parameters, such as frequent cross-relaxation and concentration quenching occurring. In order to overcome the restrictions of the RE ion multi-doped system, an efficient RE ion single-doped ultra-broadband signal amplification medium must be developed. The commercial Er3+-doped fiber amplifiers (EDFA) based on silicate glass have low linewidths, which reduce NIR transmission [5,6,7,8].

In consideration of this, new glass host matrices containing rare earths with extended lifetimes for signal amplification in optical telecommunications must be searched for. Pr3+, a trivalent rare earth ion, displays broad near-infrared luminescence as a result, which is required for optical fiber amplifiers that operate in the O-, E-, S-, C-, and L-bands [1,2] in the 1.2 to 1.7 m wavelength range of 1.2 to 1.7 μm.

Studies in the past have shown the optical amplification potential of Pr3+ ions existing in a variety of inorganic glasses, particularly those with low-loss NIR transmission windows [3,8]. Low-loss NIR luminescence in the 1D2 → 1G4 transition of Pr3+ transition correlates to super broadband NIR luminescence.

In heavy metal oxide glasses, the luminescence spectroscopy of Pr3+ ions was studied in [9,10,11,12,13]. As a result of energy transfer from Pr3+ to Yb3+ ions, we recently described the intense NIR emission at 1000 nm with a down-conversion mechanism under excitation of 445 nm [14]. The down-conversion processes in Pr3+/Yb3+ co-doped devices that convert a blue photon into two NIR photons have also been reported. Trivalent Yb3+ emission at 1000 nm may be captured by silicon solar cells without any losses (1.05 eV) because its single 2F5/2 excited state is close to the silicon band gap [15].

Fiber lasers and optical amplifiers have revealed the phosphate glasses to be an excellent product because of their superior thermal stability, flexibility, and mechanical strength [6,7,16]. For the first time, near-IR luminescence has been seen in 40P2O5-30ZnO-20LiCl-10BaF2 glasses with single doped 3.5 × 104 ppm of Pr3+, which we describe in this paper. As an additional factor, the Pr3+ ligand field was modified by the addition of certain halides (F− and Cl−). Moreover, we estimated the spectroscopic parameters viz. branching ratio, radiative lifetime, spontaneous emission probability, and quantum efficiency of the 1D2 level of Pr3+. The results show that the produced glass may be used to create broadband fiber amplifiers that operate in optical communications.

2. Experimental Work

Glass composed of 40P2O5-30ZnO-20LiCl-10BaF2 in mol% doped with 3.5 × 104 ppm Pr2O3 is referred to as (PZLBPr), which has a high homogeneity. Following the melt quenching method, we used a muffle furnace to melt the chemical at 1150 °C for one hour after stirring it in a platinum crucible. A copper mold was then used to cast the molten chemical combination. The annealing procedure started with a 2 h heat treatment of the quenched glass at 440 °C to remove any strain from the produced glasses. To investigate the amorphous characteristics of produced glasses, the powder X-ray diffraction pattern (XRD-Philips PW (1140) diffractometer and copper target (K = 1.54) were used.

A gas pycnometer was used to determine the density of the glass (Model: UltraPyc 1200 e). The density of the PZLBPr glass sample was measured to be 3.837 ± 0.00015 g/cm3. The optical absorption spectra of the glasses were determined in the wavelength range of 190–2500 nm using a UV-VIS-NIR spectrophotometer (JASCO, V-570). The short pulse stimulation was carried out using an optical parametric oscillator operated by a third harmonic of a Nd:YAG laser, and the luminescence decay curves were obtained as a result. Using an Optron Dong Woo fluorometer system, the photoluminescence spectra were measured [17].

The following equation may be used to determine the Pr3+ ions concentration [13]: where M is the PZLBPr glass’s molecular weight and A is the Avogadro’s number. In this PZLBPr glass, the dopant Pr3+ concentration is NPr3+ = 1.3628 × 1027 ions/m3.

3. Results and Discussion

To determine whether the produced glasses are amorphous or crystalline, XRD analysis was performed. Figure 1 displays the XRD patterns of the samples of prepared glasses. The X-ray amorphous patterns can be observed in the data, and because the indicated crystalline phase had not developed the amorphous nature was anticipated. According to the photo of prepared glasses PZLBPr in Figure 2b, they were transparent and homogenous. According to Figure 2a, the PZLBPr sample’s UV-Vis-NIR absorption spectrum exhibits peaks at wavelengths around 444, 466, 476, 590, 1014, 1538, 1942, and 2354 nm that correspond to transitions from the ground state of 3H4 to excited states of 3P2, 3P1, 3P0, 1D2, 1G4, 3F4, 3F3, 3F2, and 3H6, respectively. The transition from 3H4 to 3F3 has the highest peak, whereas the transfer from 3H4 to 1G4 has the lowest peak. The occurrence of all these peaks is in agreement with findings regarding other glasses doped with Pr3+ [18,19,20,21,22].

Figure 1

XRD profile of prepared glasses.

Figure 2

(a) PZLBPr glass absorption spectra, with each peak’s transition state specified; (b) photograph of the prepared glasses after annealing.

The value of optical energy gap, E, is calculated using the basic relation established for amorphous materials by Mott and Davis [23] based on the absorption coefficient (α) and the photon energy (hv) as follows: where m changes based on the interband transition process and C is a constant. As shown in Figure 3, the best fit to the observed data showed that m = 2 indicated the indirect allowed transition in the gap of the prepared glass, which means that it is a suitable method for the prediction of the optical energy gap and optical properties of glass materials.

Figure 3

Relation between (hαν)0.5 vs. hα of PZLBPr glasses.

The indirect transitions allowed in inorganic glasses are represented by a straight line at (αhν)1/2 = 0, with an hν axis in Equation (2), which illustrates the prepared glasses (see Figure 3). The results obtained showed that the value of E is 4.72 ± 0.01 eV for PZBLPr glass. It has the highest value of E compared to tellurite glass and other glass doped with the Nd3+/Yb3+ system that have been reported previously [24,25,26,27]. This is due to the presence of Pr3+ ions, which leads to an increase in both the width of the localized state in the forbidden gap and the density of electrons, therefore, increasing the probability of electronic transition from the valence band to the conduction band.

The incorporation (F, Cl) improved the phosphate glass matrix by increasing the solubility of rare earth, which means that the glass network can form more than one electric dipole environment for rare-earth ions. Consequently, the fluorescence line shape and radiative and non-radiative rates may be created in hybrid glass structures. Furthermore, the F and Cl ions in the prepared glass reduce the OH− and Pr3+ ions, which enter the lattice sites by replacing OH ions. Furthermore, the halide ions F− and Cl− can lead to an increase in the ionicity and consequently decrease the covalency of the network structure of matrix glasses, which results in a larger optical energy gap when compared to oxide phosphate glasses reported in the literature [28,29,30]. This can be considered an advantage because the wide band gap of this glass can form an excellent medium with doping or co-doped rare earth to produce superior materials that can be used in optical telecommunication at ultrabroad NIR.

Here, we determine the Urbach energy, E, using the relationship between the photon energy (hν) and optical absorption coefficients in glasses established by [23]. where A is a constant and E is the Urbach energy corresponding to the extent of the tail of localized states in the band gap. The phonon-assisted indirect electronic transitions are responsible for E. The reciprocals of the slopes of the linear component of the ln(α) vis. hν curves in the lower photon energy areas were used to calculate the E value (0.07 eV) (see Figure 4).

Figure 4

The relation between ln(α) vis. hν of PZLBPr glasses.

The Judd–Ofelt (JO) analysis was used to calculate the spectroscopic characteristics of this glass system using the absorption intensities of Pr3+-doped PZLBPr. A basic description of the JO analysis is provided here. The literature [31,32,33] includes all the applications of the JO model.

The formula below yields the measured line strength of a particular band: where l is the studied sample’s thickness (6.22 mm), c is the speed of light, h is Planck’s constant, e is the elementary charge, J is the angular momentum of the initial state, N is the density of ions, λ is the mean wavelength of the absorption bands, and is the experimental integrated optical density in the wavelength range. This density can be determined by calculating the total area under the absorbed band.

For many transitions of the Pr3+ ion, the contribution of the magnetic dipole, , to the observed line strength is generally small [19,22,34,35]. Because of this, the magnetic-dipole contribution was neglected in the prepared glasses. Table 1 depicts the results of the line-strength calculations and intensity measurements for the selected transitions.

Table 1

The results of the line-strength calculations and intensity measurements for the transitions performed.

	λ (nm)	ν (cm−1)	||U2||2	||U4||2	||U6||2	Γ (nm·cm−1)	Sexp (10−24 m2)	Scal (10−24 m2)
3H4 → 3P2	445	22471	0	0.0362	0.1355	19.11	0.54705	0.30554
3P1	462	21652	0	0.1707	0	7.51	0.20720	0.28026
3P0	476	21012	0	0.1728	0	14.61	0.39129	0.28371
1D2	590	16956	0.0026	0.017	0.052	10.31	0.22271	0.12241
3F3	1541	6490	0.0654	0.3469	0.6983	215.68	1.78360	1.83910
3F2	1958	5106	0.5089	0.4032	0.1177	137.06	0.89182	0.88521

On the other hand, in the Judd–Ofelt theory, the line strength between the initial state J characterized by (S, L, J) and the final state J′ given by (S′, L′, J′) can be calculated using the following expression [31,32,33]. where Ω (t = 2, 4, 6) denotes the doubly reduced matrix elements and t represents the Judd–Ofelt parameters. ||U2 (t = 2, 4, 6) represent the reduced matrix elements utilized for the absorption transitions of this Pr3+-doped glass presented in Table 1 and includes the ||U(||2 matrix elements estimated by Carnall et al. [36] and evaluated by Kaminiskii [37].

The values of the three JO parameters were obtained by fitting the measured and computed line strengths of the absorption transitions using Equations (4) and (5). To calculate the Ω (t = 2, 4, 6) parameters for the PZLBPr sample under study, a least square fitting of values to was used.

When using all absorption transitions, it was found that the resulting Ω2 parameter was negative, which from the definition is not acceptable. This controversial result is noticed in many compounds with Pr3+ ions [38,39,40].

Several methods have been proposed to resolve this problem, namely, the use of the modified JO theory [38,41]. The modified JO theory developed by Kornienko et al. [22,41,42,43] considers higher-order contributions in the forced electric dipole matrix elements; the resulting calculated line strength is provided using:

E′, E, and E4 are the energies of the upper, lower states, and barycenter of the 4f configuration, respectively, the parameter α is used as a fitting parameter.

The Kornienko et al. [42] modified JO theory was used in this study with the value of the parameter α fixed to 10−5 cm as it is often estimated for Pr3+glasses [22,43]. The procedure of the modified JO theory did not solve the problem and the Ω2 value is still negative.

Another approach to overcoming this problem consists of excluding one of the absorption transitions from the fitting procedure [40,44,45,46,47]. For this Pr3+ sample, the exclusion of the 3H4 → 3F4 transition from the computation is investigated. Notably, absorptions due to transitions from the ground state up to 3F4 and 3F3 levels strongly overlap. In several studies, those two levels are combined into one: the (3F4, 3F3 → 3H4) transition. Furthermore, a close observation of the absorption transition matrix elements of the Pr3+ ion shows that the Ω2 parameter depends essentially on the 3H4 → 3F2 transition because of the high value of .

Without accounting for the 3H4 → 3F4 transition, the Ωt numeric calculation produces an acceptable result. Table 2 presents JO parameters of Pr3+ in PZLBPr glass and Pr3+-doped in other hosts. The calculated Judd–Ofelt parameters are in good agreement with literature values for Pr3+-doped glasses [19,20,38,48]: similar trends (Ω2 < Ω4 < Ω6) have been found in PPbKANPr [19], TeO2-PbF2-AlF3-PrF3 (TPA) [38], ASL [44], PTBPr [43], and Ca5(PO4)3F [48] glasses.

Table 2

Comparison of the PZLBPr glass Judd–Ofelt parameters (Ωt × 10−20 cm2) with those of other systems.

System	Ω2	Ω4	Ω6	Trend	χ
PZLBPr [Present Work]:	0.018	1.641	1.816	Ω2 < Ω4 < Ω6	0.90
PPbKANPr0.5 [19]	1.51	18.03	19.81	Ω2 < Ω4 < Ω6	0.91
Phosphate [49]	4.19	4.29	6.40	Ω2 < Ω4 < Ω6	0.67
ZNBBP [50]	1.7	3.06	4.72	Ω2 < Ω4 < Ω6	0.64
BPGBPr [51]	0.70	2.96	7.03	Ω2 < Ω4 < Ω6	0.42
Oxyfluoride [52]	0.66	12.49	3.17	Ω2 < Ω6 < Ω4	3.94
Ca5(PO4)3F [48]	0.32	1.59	3.82	Ω2 < Ω4 < Ω6	0.41
LaF3 [53]	0.12	1.77	4.78	Ω2 < Ω4 < Ω6	0.37
LiPrP4O12 [53]	1.82	2.83	6.54	Ω2 < Ω4 < Ω6	0.43
YAlO3 [53]	2.00	6.00	7.00	Ω2 < Ω4 < Ω6	0.85
LiYF4 [53]	0.00	8.07	7.32	Ω2 < Ω6 < Ω4	1.10
Oxy–Fluoride [21]	0.13	4.09	6.33	Ω2 < Ω4 < Ω6	0.64
TPA(n = cst) [38]	0.48	1.39	13.5	Ω2 < Ω4 < Ω6	0.10
TPA (n ≠ cst) [38]	0.92	1.85	6.61	Ω2 < Ω4 < Ω6	0.27
TeO2-Li2CO3-Pr2O3 [38]	3.81	5.81	4.1	Ω2 < Ω6 < Ω4	1.41
PTBPr [43]	3.07	3.36	8.68	Ω2 < Ω6 < Ω4	0.38

The acquired Ω values are utilized to obtain the rms deviation and recalculate the transition line strengths S of the absorption bands using Equation (3). In our work, the rms deviation was determined to be 1.4868 × 10−25 m2. The significant mixing between the 4f and 5d orbitals may account for the increased rms difference between the estimated and observed oscillator strengths in the case of Pr3+ ions. The covalency, ionic composition, and symmetry of the RE ion’s site are all factors connected to the Ω2 parameter. In contrast, values Ω4 and Ω6 are closely connected to the basicity, hardness, and dielectric properties of the glass samples [19]. With an increase in the hardness of the host matrices’ surroundings, Ω6 decreases. In the present PZLBPr glass, the trend from Ω2 < Ω4 < Ω6 showed that there was more asymmetry and less covalency within the PrO group. The stimulated emission cross-section for the laser active medium is predicted by the spectroscopic quality factor χ = Ω4/Ω6, which is found to be around 0.9 for this PZLBPr glass and similar to the value for the PPbKANPr0.5 sample [19].

According to Table 2, the range of the spectroscopic quality factors for Pr3+ doped in various hosts is between 0.20 and 1.64.

For a change from a higher J′ to a lower J-multiplet, the spontaneous emission probability A is computed as follows:

is the corresponding emission line strength calculated from Equation (6) using the value of Ω. In addition, the following formulas might be used to determine the radiative lifetime for electric dipole transitions between an excited state (J) and the lower-lying terminal manifolds (J′):

Over all final states (J′), the total of τ is calculated and the sum is taken over all final states J′.

The fluorescence branching ratio, β, is an important statistic for the laser designer since it describes the potential of achieving a stimulated emission from a certain transition and predicts the relative strength of lines from specified excited states.

Table 3 shows the PZLBPr glass system’s spectroscopic properties; (), (τ), and (β) of excited states 3H4, 3H5,3H6, 3F2, 3F3, 3F4, 1G4, 1D2, 3P0, 3P1, and 3P2 of Pr3+ ions in the PZLBPr glasses.

Table 3

The spectroscopic parameters of the PZLBPr glass system.

Transition		Wavelength (nm)	A (s−1)	τ (ms)	β (%)
3P2 →	3H4	431.77	4393.6	0.040	17.6
	3H5	476.0	5891.9		23.7
	3H6	532.72	7053.9		28.3
	3F2	550.54	3420.7		13.7
	3F3	597.18	2776.2		11.1
	3F4	613.28	1078.3		4.3
	1G4	755.32	268.29		1.1
	1D2	1716.4	26.99		0.1
	3P0	5647.2	0.023		0.0
	3P1	8671.9	0.013		0.0
3P1 →	3H4	454.39	5762.6	0.076	43.9
	3H5	503.64	0		0.0
	3H6	567.59	1391.1		10.6
	3F2	587.86	47.37		0.4
	3F3	641.35	2435.6		18.6
	3F4	659.95	3141.5		24.0
	1G4	827.39	338.42		2.6
	1D2	2139.9	0.2739		0.0
	3P0	16190	0		0.0
3P0 →	3H4	467.51	16068	0.041	67.4
	3H5	519.81	150.98		0.6
	3H6	588.21	3329.6		14.0
	3F2	610.01	139.41		0.6
	3F3	667.80	0.00		0.0
	3F4	687.99	3539.2		14.8
	1G4	871.95	609.13		2.6
	1D2	2465.8	0.10		0.0
1D2 →	3H4	576.89	737.95	0.147	47.8
	3H5	658.66	14.84		1.0
	3H6	772.48	294.00		19.1
	3F2	810.52	291.04		18.9
	3F3	915.82	42.40		2.7
	3F4	954.23	49.17		3.2
	1G4	1349.0	113.84		7.4
1G4 →	3H4	1007.9	18.33	3.096	5.7
	3H5	1287.1	218.72		67.7
	3H6	1807.6	71.32		22.1
	3F2	2030.6	2.19		0.7
	3F3	2852.3	2.42		0.7
	3F4	3261.1	9.96		3.1
3F4 →	3H4	1458.8	199.48	4.995	99.7
	3H5	2126.5	0.00		0.0
	3H6	4055.7	0.00		0.0
	3F2	5381.7	0.69		0.3
	3F3	22,753.0	0.01		0.0
3F3 →	3H4	1558.8	401.43	2.489	99.9
	3H5	2345.7	0.00		0.0
	3H6	4935.5	0.00		0.0
	3F2	7049.1	0.20		0.01
3F2 →	3H4	2001.4	127.81	7.823	100
	3H5	3515.5	0.00		0.0
	3H6	16,460.0	0.00		0.0
3H6 →	3H4	2278.4	11.59	86.286	100
	3H5	4470.3	0.00		0.0
3H5 →	3H4	4646.6	0.00		0.0

It is observed that the lifetime trend decreases as 3H6 >> 3F2 > 3F4 > 1G4 > 3F3 > 1D2 > 3P1 > 3P0~3P2. There is a decreasing tendency of branching ratios for the emission transitions, 3F2 → 3H4 > 3F3 → 3H4 > 3F4 → 3H4 > 3P0 → 3H4 > 1G4 → 3H5 > 1D2 → 3H4 > 3P1 → 3H4 > 3P2 →3H4. The branching ratios of 3P0 → 3H4 (blue) and 1D2 → 3H4 (red) transitions are estimated to be 67% and 47%, respectively. Thus, the blue and red/orange emissions are expected to be dominant among all visible transitions. An interesting result is that the branching ratio for the 1G4 → 3H5 transition is larger than the 1G4 → 3H4 transition. Precisely, 1G4→ 3H5 presents an elevated fluorescence branching ratio (β ~ 67%) characterizing the lasing potential of this transition, in the near-infrared region. Since the 1G4 level has a sufficiently large energy gap with respect to the next lower level 3F4, it emits via purely radiative relaxations an infrared fluorescence emission as shown in Figure 5. It should be noted that the 1G4 level is efficiently pumpable at 1.01μm, especially that high population inversion could be obtained, given that the excited initial state, (3H5), relaxes directly to the ground state seeing the higher branching ratio of the 3H5 → 3H4 transition.

Figure 5

Energy level diagram of Pr3+ ions.

The PL emission spectra of the prepared glass excited at 445 nm are shown in Figure 6. The 3P0 → 3H4, 3P0 → 3H5, 1D2 → 3H4, 3P0 → 3H6, and 3P0 → 3F2 transitions of Pr3+ are responsible for the emission bands shown at 485, 525, 550, 600, and 640 nm, respectively. The type of glass host has a significant influence on the intensity of emission bands in the blue and reddish orange range. Two prominent transition peaks in the visible emission spectrum are attributed to 3P0 → 3H4 (blue) and 1D2 → 3H4/ 3P0 → 3H6 (red/orange). The higher sub-levels of 3P0 energy may be absorbed by a surrounding Pr3+ in the ground state when they are close together, which causes a decrease in the higher energy levels of 3P0. The spectrum of 3P0 ↔ 3H4 overlaps the high-energy emission and low-energy absorption sides.

Figure 6

VIS PL emission spectra of PZLBPr under excitation 445 nm.

Furthermore, compared to the 3P0 →3H4 transition, the emission intensity increase from the 1D2 state is significantly lower. Because of the population or depopulation of the 1D2 state of Pr3+ ions in host glasses is significantly influenced by multi-phonon relaxation and cross relaxation. Pr3+ ions undergo the 3P0 → 3H4 transition as the excitation energy is changed from the lower 3P0 state to the 1D2 state, resulting in reddish orange luminescence. Under 445 nm excitation, Bo Zhou et al. [5] examined the visible PL spectra of Pr3+ doped fluorotellurite glasses. They determined that the mission bands at wavelengths of 490, 528, 611, and 643 nm, respectively, correspond to the Pr3+ transitions of (3P1, 3P0) → 3H4, 3P0 → 3H5, (3P1, 3P0) →3H6, and 3P0 → 3F2, respectively. Our data are excellent agreement with those of other glasses described in Refs. [5,54,55,56]. As a consequence, we can conclude that PZLBPr is a high phonon glass that can occupy the energy gap between the visible range 3P0 and 1D2 states of Pr3+ ions and the red/orange emission caused by 1D2 → 3H4.

Figure 7 displays the NIR luminescence emission spectra of PZLBPr-produced glass excited by 445 nm (3P2) at wavelengths between 850 and 1700 nm. Observing that the (1D2 → 3F3, 3F4) and (1G4 → 3H5) and (1G4 → 3H5) transitions of Pr3+ are responsible for the near-infrared luminescence bands at 1030 and 1350 nm is significant for optical fiber amplifiers operating in the second telecommunication window [53,55,56]. The 1D2 → 1G4 transition of Pr3+ is responsible for the strong NIR luminescence band with a center wavelength of around 1460 nm. The ultra-broadband near-infrared fluorescence band 3F3, 3F4 → 3H4 transition at around 1685 nm also contributed. As can be seen in Figure 7, the full-width at half-maximum (FWHM) for the equivalent 1D2γ 1G4 transition emission is 156nm, which indicates that the PZLBPr glass is very suitable for broadband amplification of E-, S-, C-, and L-bands.

Figure 7

NIR PL emission spectra of PZLBPr under excitation at 445 nm.

According to X. Liu et al. [1], the associated 1D2 → 1G4 transition emission has a 140 nm full-width at half-maximum (FWHM), which enables Pr3+-doped NZPGT glasses attractive for broadband amplification covering the entire E-, S-, C-, and L-bands. The ultra-broadband emission at 1.48 μm has a peak in intensity at 1476 nm. Additionally, previous findings in [1,2,57,58] suggest that Pr3+-doped borate, phosphate, and silicate glass fiber amplifiers operating in the fifth optical communications window may be useful (1380–1525 nm): the PZLBPr glass is a better choice for usage in optical communication devices as it has a greater FWHM of the transition emission of 1D2 → 1G4 (156 nm) than the present glass does.

The lifetime values are calculated using the formula: , where the decay curve is dependent on time, as shown in [14,17]. Figure 8 depicts the PL decay of stimulated levels. The radiative lifetime, estimated to be 147.1 μs, and the experimental lifetime, estimated to be 128.4 μs by fitting the fluorescence decay curve, are used to calculate the quantum efficiency, , for a luminescence level of 1D2 to 1G4. The near-infrared emission from the 1D2 level is efficient for creating optical signal amplification in a specific optical communications band, as shown by the quantum efficiency of the Pr3+: 1D2 level, which is equivalent to 87.3%. Together, these findings demonstrate that PZBLPr glass’s specific optical communications band may effectively produce optical signal amplification via the near-infrared emission at the 1D2 level.

Figure 8

The Pr3+: 1D2 fluorescence decay level of PZLBPr under excitation at 445 nm.

4. Conclusions

The incorporation of halide ions (F− and Cl−) with Pr3+ ions into the present phosphate matrix leads to improvement of the high value of the optical energy gap compared to some phosphate glasses reported previously. The valuation of Judd–Ofelt parameters of PZBLPr glasses achieved the following: (Ω2 = 0.0181 × 10−20 cm2, Ω4 = 1.641 × 10−20 cm2, Ω6 = 1.816 × 10−20 cm2). The trend of Ω2 < Ω4 < Ω6 that occurred in the studied glasses indicated higher asymmetry and lower covalency between Pr-O groups. In addition, the halide ions led to a decrease in the covalency otherwise an increase in the ionicity of the structure of PZBLPr glasses. The large quantum efficiency of Pr3+:1D2 (=87.3%) with full-width at half maximum of 156 nm was reported in PZLBPr glass. Therefore, based on this analysis, it can be concluded that PZLBPr glass has potential for broadband near-IR functioning and can have its communications transmission window increased at 445 nm.