Optical properties of Nd3+-doped phosphate glasses

Optical properties of Nd3+-doped phosphate glasses

Optical Materials 99 (2020) 109591 Contents lists available at ScienceDirect Optical Materials journal homepage: http://www.elsevier.com/locate/optm...

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Optical Materials 99 (2020) 109591

Contents lists available at ScienceDirect

Optical Materials journal homepage: http://www.elsevier.com/locate/optmat

Optical properties of Nd3þ-doped phosphate glasses Mahmoud M. Ismail a, *, Inas K. Batisha a, Lidia Zur b, Alessandro Chiasera b, **, Maurizio Ferrari b, c, Anna Lukowiak d a

Solid State Department, Physics Division, National Research Centre (NRC), Cairo, Egypt IFN-CNR CSMFO Lab. and FBK Photonics Unit, Povo, Trento, Italy c Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Piazza del Viminale 1, 00184, Roma, Italy d Institute of Low Temperature and Structure Research, PAS, Okolna, 2, 50-422, Wroclaw, Poland b



Keywords: Phosphate glasses Rare earths Neodymium ions Photoluminescence Glass photonics Judd-Ofelt analysis Spectroscopic quality factor

Multi-component phosphate glasses with various Nd2O3 content have been prepared using conventional meltquenching technique. X-ray diffraction was carried out to study the structure of the prepared samples and it was found that all the obtained samples are amorphous. Electrostatic F(2), F(4), F(6), and spin–orbit parameters have been determined from the absorption spectra. Judd-Ofelt theory has been used to analyze and evaluate the radiative transition probability, branching ratio, and radiative lifetime for the metastable level 4F3/2. Lumines­ cence spectra and experimental lifetimes give information regarding the absence of chemical clustering and suggest that the physical clustering is negligible making the glass a suitable candidate for photonic applications.

1. Introduction The first neodymium glass laser has been proposed in 1961 by Elias Snitzer at American Optical company [1]. From that time, several different neodymium doped glass matrices have been intensively investigated, such as Nd3þ doped fluorides [2–5], chalcogenides [6], aluminosilicates [7], germanates [3], and tellurite glasses [8–10]. Among all oxide glasses, phosphates have received more interest because their high rare earth ions solubility and consequently clustering reduction, resulting in an increase of a luminescence quantum yield, a wide transparency typically in the 0.2–6 μm range, and a non-linear refractive index smaller than for Nd silicate laser glasses [5]. Network intermediates (Al2O3), alkali metal oxides (Na2O and K2O), and alkaline earth metal oxides (BaO) can be added to enhance the chemical, me­ chanical, and thermal stability of phosphate glasses [11]. Neodymium ions have laser lines around 946 nm, 1060 nm, and 1319 nm corresponding to the 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, and 4F3/2 → 4 I13/2 transitions, the most efficient one is at about 1060 nm. This intense emission at 1060 nm has been already investigated for high power laser applications [12]. The main objective of the present work is dedicated to the prepara­ tion of multi-component phosphate glasses doped with Nd3þ ions and to their characterization. The structure and the spectroscopic properties of

the Nd-doped glasses are studied to develop a suitable glass composition and to choose the most promising neodymium concentration for optical amplifier and laser applications. Additionally, Judd-Ofelt [13,14] cal­ culations are carried out, and the obtained parameters are compared with the ones previously published. 2. Experimental details 2.1. Glass preparation Multi-component phosphate glasses with the molar composition of 60P2O5–8Al2O3–2Na2O–17K2O-(13-x)BaO-xNd2O3, (where x ¼ 0, 0.5, 0.75, 1.0, and 1.5) further described as PANKB0Nd, PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd and PANKB1.5Nd, were prepared using conventional melt-quenching technique. High purity P2O5, Al2O3, Na2CO3, BaCO3, K2CO3, and Nd (NO3)3⋅5H2O were used as starting materials to prepare the mentioned glasses. A batch of 30 g of starting materials was thoroughly mixed in agate mortar and the homogeneous mixture was taken in a porcelain crucible and kept in an electric furnace at a temperature of 1100 � C for 2 h. The melting was then poured onto a preheated stainless steel mold at a temperature of 430 � C until the glass solidifies. The glass samples were then annealed at the same temperature, 430 � C, for 10 h to remove

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M.M. Ismail), [email protected] (A. Chiasera). https://doi.org/10.1016/j.optmat.2019.109591 Received 2 November 2019; Received in revised form 28 November 2019; Accepted 29 November 2019 Available online 5 December 2019 0925-3467/© 2019 Elsevier B.V. All rights reserved.

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thermal strains and stress. After that, the samples were cooled down to room temperature. Finally, the prepared glasses were cut and polished for optical measurements.

composition. In the case of density, although the variation is in the range of the experimental error, we observe that it decreases with the increasing Nd2O3 content up to 0.75 mol% and then increase to finally stabilize at the value of the undoped sample. Being the molecular weight of Nd2O3 higher than that of BaO, a continuum increase in the density should be expected. However, Mohan et al. suggest a role of Nd3þ in the formation of non-bridging oxygens to explain a similar behavior observed in Nd3þ-doped sodium-lead-borate glasses [15]. This aspect surely deserves deeper investigation. Fig. 2 shows the absorption spectra of PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd glasses in the region from 300 nm to 1800 nm. The spectra consist of 11 bands corresponding to the transi­ tions from the ground state 4I9/2 to the various excited states,4I15/2, 4F3/ 4 2 4 4 4 2 4 2 2 4 2, F5/2þ H9/2, F7/2þ S3/2, F9/2, H11/2, G5/2þ G7/2, K13/2þ G7/ 4 2 2 2 4 2 2 4 4 þ G , K þ G þ P þ G , P þ D , and D þ D5/ 2 9/2 15/2 19/2 3/2 11/2 1/2 15/2 3/2 2 4 2þ I11/2þ D1/2, respectively. The absorption bands are assigned by comparison with energy levels of previously reported Nd3þ glass systems [3]. The absorption coefficient increases by increasing Nd3þ ions con­ centration. It is worthy to note that the linear increase of the absorption with the Nd content indicates the absence of rare earth chemical clustering. Table 2 shows the F(2), F(4), F(6), and ζ parameters for the PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd glasses. Table 3 shows the calculated and experimentally observed energy levels for PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd and PANKB1.5Nd glasses. The experimental values of the energy levels have been obtained from the absorption spectra. The calculated values are obtained as described in Refs. [15–17]. More in detail, the electrostatic F(2), F(4), F(6), and spin-orbit (ζ) parameters have been obtained using the Rare Earth Level and Intensity Calculations (RELIC) program [16,17] (Table 2). The program performs a least-squares fit of calculated energy levels to the set of experimental energy levels by adjusting the F(k) and ζ intermediate coupling parameters. The function to minimize, in order to obtain Ecalc (Table 3), is the sum of the squares of the relative errors on the energies. The good agreement between experimental and calculated energy indicates the good fitting of the electrostatic (F(2), F(4), F(6)) and spinorbit (ζ) parameters. The experimental oscillator strengths (fexp) for all the absorption bands of Nd3þ ions can be determined from the absorption spectra using the expression given by Z Z mc2 9 fexp ðΨJ → Ψ’ J ’ Þ ¼ ε ð υ Þd υ ¼ 4:318 ​ ​ X ​ 10 εðυÞdυ (1) π e2

2.2. Characterization techniques The density of the samples was determined by Archimedes’ method with water as an immersion liquid. X-ray diffraction (XRD) patterns of the prepared samples were recorded with a Philips X-ray diffractometer using monochromatized CuKα1 radiation of wavelength 1.54056 Å from a fixed source operating at 45 kV and 9 mA. The refractive indices of these glasses have been measured using a PTR 46X refractometer at 589 nm with the monobromonapthalene as the contact layer between the sample and the prism of the refractometer. Absorption spectra in the range 200–1800 nm were measured using a V-570 UV/VIS/NIR spec­ trophotometer with a spectral bandwidth of 0.5 nm, a resolution of 0.1 nm, and a wavelength accuracy of �0.3 nm. The measurements were made on the glasses and glass powders immediately after glass prepa­ ration. All measurements were performed at room temperature. The photoluminescence spectra and the lifetime measurements were performed by exciting the samples with a diode laser at 514.5 nm. The excitation power was 0.5 mW for all the measurements. The lumines­ cence signal was dispersed by a single grating monochromator with a resolution of 0.5 nm and 2 nm for the emission and excitation spectra, respectively, and was detected using a Hamamatsu photomultiplier and standard lock-in technique. Absolute photoluminescence quantum yields (internal quantum efficiency) of the investigated system have been obtained using the Hamamatsu Quantaurus-QY C11347-01. As a light source 150 W xenon lamp was used, using the excitation of 515 nm. The photoluminescence measurement wavelength range was from 300 to 950 nm. 3. Results and discussion The structural properties of the obtained phosphates glasses have been examined by XRD. Fig. 1 shows the XRD patterns of PANKB0Nd (a), PANKB0.5Nd (b), PANKB0.75Nd (c), PANKB1Nd (d) and PANKB1.5Nd (e). On each pattern, very broad peak, extending from 2Ѳ ¼ 12 up to 2Ѳ ¼ 40, is observed. The obtained patterns, without any visible crystalli­ zation peaks in the whole measured range for all the samples, would confirm the amorphous phase of the undoped and neodymium doped samples. Table 1 shows the refractive index and the density of the samples. The refractive index does not change with the variation of the

where m and e are the mass and the charge of an electron, respectively, c is the speed of light, υ is the wavenumber (in cm 1), and ε is the molar absorptivity. According to Judd-Ofelt (J-O) theory [13,14] the total oscillator strength can be calculated using equation (2) fcalc ðΨJ → Ψ’ J ’ Þ ¼

8π 2 mν0 ½ χ Sed þ χ md Smd � 3hð2j þ 1Þn2 ed


where Sed and Smd are the electric and magnetic dipole line strengths; χ ed ¼ n(n2þ2)2/9 and χ md ¼ n3 are the Dexter correction for the local field in a medium of refractive index n.

Table 1 Refractive indices (n) and densities (ρ) of the prepared samples.

Fig. 1. XRD patterns of PANKB0Nd (a), PANKB0.5Nd (b), PANKB0.75Nd (c), PANKB1Nd (d), and PANKB1.5Nd (e) phosphate glasses. 2

Glass sample

n (�0.01)

ρ (�0.03) [g/cm3]


1.65 1.65 1.65 1.65 1.65

2.76 2.75 2.73 2.79 2.76

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Fig. 2. Absorption spectra of PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd glasses.

Sed ðΨJ → Ψ’ J ’ Þ ¼

i 8π2 mν0 χ ed h X 2 Ωt jijjU t jjjj 3hð2j þ 1Þn2 t¼2;4;6

following equation [20]:


Ar ðΨJ → Ψ’ J ’ Þ ¼ e2 h2 χ md Smd ðΨJ → Ψ J Þ ¼ jijjL þ 2Sjjjj2 16π2 m2 c2 ’ ’


# " 2 64π4 ν20 e2 nðn2 þ 1Þ Sed þ n3 Smd 3hð2j þ 1Þ 9


Where Sed and Smd are the electric and magnetic dipole line strengths, respectively, which are expressed as X 2 Sed ðΨJ → Ψ’ J ’ Þ ¼ Ωt jJjjU t jjJ ’ j (6)

where Ωt (t ¼ 2, 4, and 6) are Judd-Ofelt intensity parameters, m is the electron mass, υ0 is the wavenumber at the absorption maximum, h is the Plank constant, 2J þ 1 is the degeneracy of the originating level of the transition and ijjUt jjj are the doubly reduced matrix elements of the tensor transition operator and they have been calculated as in Refs. [15, 17] using RELIC program [16]. The Judd-Ofelt intensity parameters, Ωt (t ¼ 2, 4, and 6) were determined using standard least-square fitting approach between experimental (fexp) and calculated (fcalc) oscillator strength. The obtained values are reported in Table 4, together with some of those present in the literature for other Nd-doped systems. The J-O in­ tensity parameter Ω2 is related to the sensitivity to the local glass structure of the rare-earth sites and it is affected by the covalence be­ tween Ln3þ ions and their surrounding ligands. Greater Ω2 value is, higher is the degree of covalence between rare-earth ions and the nearest surroundings. The Judd-Ofelt parameters presented in Table 4 have different trend for different content of Nd3þ ions in phosphate glasses. Being Judd-Ofelt parameters obtained by the oscillator strengths of the transitions observed in the absorption spectra, this behavior suggests an effective role of Nd3þ ion in constructing their local envi­ ronment. We will see that this role is confirmed by the quantum effi­ ciency assessment. Additionally, the emission intensity of Nd3þ-doped laser glasses is characterized by the intensity parameters Ω4 and Ω6 which can be used for the evaluation of the spectroscopic quality factor χ (¼Ω4/Ω6) useful in predicting the stimulated emission for the laser active medium [18]. The most efficient transition 4F3/2 → 4I11/2 is ob­ tained at around 1060 nm for Ω6≫Ω4. The spectroscopic quality factor was found to be 0.54 for the glass doped with 1.5 mol% of Nd3þ. The obtained results for all the investigated samples satisfy the condition Ω6≫Ω4 that indicate 4F3/2 → 4I11/2 at 1060 nm as the more efficient laser transition in our glasses [18,19]. Table 5 shows the experimental and calculated oscillator strengths of PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd glasses. The good agreement between experimental and calculated oscillator strengths indicates the good fitting of Judd-Ofelt parameters. Once the J-O parameters have been obtained, some important radi­ ative parameters can be derived such as the spontaneous emission probability (A) of an electric-dipole transition, which is given by the


Smd ðΨJ → Ψ’ J ’ Þ ¼

h2 2 jJjjL þ 2SjjJ ’ j 16π 2 m2 c2


The total radiative transition probability At ðΨJÞ for an excited level is given by the sum of the AðΨJ →Ψ’ J’ Þ terms calculated over all ter­ minal levels [20]. X At ðΨJÞ ¼ AðΨJ → Ψ’ J ’ Þ (8) The fluorescence branching ratio Br has been determined using equation (9). Br ¼

AðΨJ→Ψ’ J ’ Þ At ðΨJÞ


The radiative lifetime τr ðΨJÞ of an excited level ðΨJÞ is given by the reciprocal of At ðΨJÞ [20].

τr ðΨJÞ ¼

1 At ðΨJÞ


The obtained parameters are presented in Table 6. The branching ratio Br for the transition 4F3/2 → 4I11/2 is in perfect agreement with what was expected from the value of the spectroscopic quality factor for the investigated glasses, as discussed above [19]. Fig. 3 shows the 4F3/2 → 4I11/2 fluorescence spectra of PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd glasses. The emission Table 2 F(2), F(4), F(6), and ζ parameters for Nd-doped phosphate glasses. Parameters F(2) F(4) F(6) ζ


Glass Samples PANKB0.5Nd




332.52 48.23 5.437 909.36

330.06 48.48 5.35 913.95

331.930 48.10 5.42 915.53

330.17 48.41 5.35 916.97

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Table 3 Theoretically calculated and experimentally measured energy levels (cm 1) for Nd3þ-doped phosphate glasses. ENERGY LEVEL

Glass Samples PANKB0.5Nd


I15/2 4 F3/2 4 F5/2 2 H9/2 4 S3/2 4 F7/2 4 F9/2 2 H11/2 4 G5/2 2 G7/2 2 K13/2 4 G7/2 4 G9/2, 2 K15/2 2 G19/2 2 P3/2 4 G11/2 2 P1/2 2 D15/2 4 D3/2 4 D5/2 2 I11/2 4 D1/2








6188.1 11532.5 12468.8

6173.1 11354.9 12488 12570.4 13306.7 13465.3 14813.1 16021.2 17077.6 17187.1 18929.1 19042.1 19525 21001.5 21176.1 21203.2 21611.5 23104.6 23749.8 28229.7 28450.9 28547.2 28848.8

6163.3 11527.7 12455.7

6152.2 11351.8 12440.4 12573.6 13297 13455.4 14799.6 16012.9 17074 17185.5 18926.9 19033.7 19512.5 20992.6 21160.6 21197.4 21592.8 23095.8 23744.8 28233.7 28443.9 28540.7 28838.1

6179.8 11526.8 12468.8

13410.7 14661.3 15908 17201.1 19217.4 213432

23223.2 28128.9

13406.9 14664 15892.2 17188.2 19206.3 2138.3

23189.6 28127.5

intensity increases practically linearly with an increase of Nd3þ con­ centration. The inset shows the normalized spectra. The emission band profiles are not modified by the Nd3þ concentration indicating that the Nd3þ ions are homogeneously distributed in the glass matrix and there is no variation in the local crystal field around dopant ions. The lumines­ cence behavior indicates that the physical clustering is negligible, although the luminescence quenching due to the cross relaxation could be effective for the highly doped samples. Fig. 4 shows the emission decay curve of 4F3/2 level. The profiles are not single exponential but without important differences among them as a function of the Nd content. The experimental lifetimes, calculated at 1/e of the intensity at t ¼ 0, are reported in Table 7 and compared with those calculated in Table 6. The radiative lifetime was found to be practically constant for the investigated Nd3þ ions content. The experimental lifetime is about 0.3 ms for all the samples confirming that physical clustering is negligible, at least for concentration lower than 1.5 mol%. A similar behavior was observed previously in other glass systems activated by Nd3þ ions [21–27], although the glasses presented in this work exhibit a longer lifetime for the 4F3/2 metastable state. The quantum efficiency (Ƞ) can be calculated using the following relation [20]:


τexp τrad


χ ¼ Ω4/Ω6


PANKB0.5Nd PANKB0.75Nd PANKB1Nd PANKB1.5Nd PZNd1 [22] PKMAofNd1.0 [28] BSGdCNd0.5 [29] BNofNd1.0 [30]

2.44 2.26 2.3 1.8 5.46 7.66 2.14 5.33

1.02 1.06 0.87 1.12 3.22 5.15 2.57 2.84

2.5 2.36 2.25 2.06 4.29 6.99 1.93 4.9

0.41 0.45 0.39 0.54 0.75 0.74 1.33 0.57

Ω6 >Ω2 >Ω4 Ω6 >Ω2 >Ω4 Ω2 >Ω6 >Ω4 Ω6 >Ω2 >Ω4 Ω2 >Ω6 >Ω4 Ω2 >Ω6 >Ω4 Ω4>Ω2>Ω6 Ω2 >Ω6 >Ω4

14659.2 15905.2 17197.2 19227.8 21339.2

23247.7 28154.4

Transition from the ground state 4 I9/2 to

Glass Samples


I15/2 F3/2 F5/2þ 2H9/2 4 F7/2þ 4S3/2 4 F9/2 2 H11/2 4 G5/2þ 2G7/2 2 K13/2þ 4G7/ 4 2þ G9/2, 2 K15/2þ 2G19/ 2 2þ P3/ 4 2þ G11/2 2 P1/2þ2D15/2 4 D3/2þ4D5/ 2 2þ I11/ 4 2þ D1/2 4 4

Table 4 Judd–Ofelt parameters (Ωt x 10 20 cm2), spectroscopic quality factor (χ ¼ Ω4/ Ω6) for Nd3þ-doped phosphate glasses. Ω4


Ecalc 6124.1 11395.2 12454.4 12587.3 13310.2 13462.2 14802.5 15952.3 17108.9 17187.1 18959.4 19040.2 19518.5 21020.1 21142.1 21280.8 21598.8 23179.5 23754.2 28292.0 28526.9 28642.7 28886.9

13408.7 14664.1 15880.7 17194.8 19231.4 21336

23277.5 28254.4

Table 5 Experimental and calculated oscillator strengths of Nd3þ-doped phosphate glasses.

where τexp is the experimental lifetime and τrad is the radiative lifetime. In the phosphate glasses, the quantum efficiency is around 38% for Nd3þ


12447.3 12570.1 13307 13460.6 14810 16020 17080.7 17169.7 18943.9 19031.1 19515.1 21017 21156 21259.1 21603.4 23162.1 23739.2 28247.7 28481.8 28608.4 28852.6

Eexp 6134.2 11541.0 12463.3

ions content lower than 0.75 mol% and decreases to 28% when the Nd3þ concentration is equal to 1.5 mol%. Additionally, the photo­ luminescence quantum yield (ΦPL) which is defined as the ratio of number of photons emitted from the sample (PNem) with those absorbed by the sample (PNabs) was measured. The ΦPL under 515 nm excitation is 11.6%, 14.1%, 12.0% and 10.4% for PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd and PANKB1.5Nd glasses, respectively. The ΦPL increases with the increasing of Nd3þ content up to 0.75 mol% and then start to decrease confirming the quantum yield estimated by the ratio of experimental and calculated lifetime. The trend of the estimated and measured quantum efficiency indicates that the local environment modification of the rare earth ions for the different glasses and the possible cross relaxation processes, although not very effective, have a role in the radiative relaxation dynamics of the system. However, it is important to state that, to confirm this analysis, further data regarding a higher number of samples are necessary. Hence, the presented multi-component phosphate glasses can be considered as suitable and very promising candidate for developing



PANKB1.5Nd Ecalc














0.07 0.8 3.79 3.64 0.3 0.07 8.57 3.18

0.11 0.7 3.98 3.61 0.49 0.08 8.64 2.31

0.15 0.69 3.58 3.51 0.33 0.06 8.13 3.03

0.11 0.69 3.89 3.49 0.48 0.08 8.21 2.26

0.09 0.89 3.42 3.38 0.27 0.07 7.88 3.04

0.10 0.6 3.7 3.32 0.47 0.08 7.98 2.12

0.16 0.76 3.04 3.18 0.26 0.07 6.91 3.11

0.10 0.69 3.5 3.1 0.46 0.07 6.98 2.11









0.16 2.88

0.17 3.06

0.16 3.01

0.18 3.16

0.16 2.38

0.15 2.66

.0.15 3.04

0.18 3.2

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Table 6 Radiative transition probability (A), total transition probability (AT), radiative lifetime (τ r), and branching ratio (Br) for the excited state 4F3/2 of Nd3þ in phosphate glasses. Initial level

Final level

Glass Samples PANKB0.5Nd




I15/2 I13/2 I11/2 4 I9/2 4 4

At (s



τr (ms)�0.05



A (ms 1)


A (ms 1)


A (ms

7.33 143.77 693.17 385.48 1239 0.8

0.005962 0.116909 0.563666 0.313463

7.12 139.28 675.83 391.91 1223 0.8

0.005862 0.114718 0.556630 0.322790

6.77 133.23 633.57 340.52 1121 0.9

1.06 μm solid state laser, at least as concerns the luminescence dynamics.




A (ms 1)


0.006075 0.119589 0.568688 0.305648

6.41 125.16 616.04 394.52 1150 0.9

0.005616 0.109583 0.539378 0.345423

Table 7 The τr (ms), τexp (ms), and estimated (Ƞ) and measured (ΦPL) quantum yield of 4 F3/2 level for the prepared samples.

4. Conclusions 3þ

Nd -doped Na–Al–Ba–K phosphate glasses have been prepared by conventional melt-quenching technique. The XRD patterns of the pre­ pared samples indicate that the obtained materials are amorphous. Absorption spectra have been analyzed using the Judd-Ofelt theory. The


τr (ms)

τexp (ms)




0.8 0.8 0.9 0.9

0.3 0.3 0.3 0.25

38% 38% 33% 28%

11.6% 14.1% 12.0% 10.4%

radiative transition probability (A), branching ratio (Br), and radiative lifetime (τr) for the metastable level 4F3/2 were calculated. The emission spectra shape and intensity as well as the lifetimes measurements indi­ cate that the physical clustering is negligible for the concentration of Nd3þ ions lower than 1.5 mol%. The quantum efficiency, estimated by the ratio of experimental and calculated lifetimes, is around 38% for Nd3þ ions content lower than 0.75 mol% and decreases to 25% for the phosphate glass doped with 1.5 mol% of Nd3þ. The absolute quantum yield measured under 515 nm excitation is 11.6%, 14.1%, 12.0%, and 10.4% for a content of 0.5, 0.75, 1, and 1.5 Nd3þ mol%, respectively. The branching ratio and spectroscopic quality factor indicate that the transition 4F3/2 → 4I11/2 is the more suitable for laser action. The presented multi-component phosphate glasses exhibit spectro­ scopic properties that suggest to go deeper in further investigation on this glass for developing solid state laser in the near-infrared at a wavelength of 1.06 μm. Fig. 3. 4F3/2 → 4I11/2 emission spectra of PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd glasses excited with laser diode @ 514.5 nm. The inset shows the normalized spectra.

Authors contribution sections Mahmoud M. Ismail – sample preparation; collaboration in mea­ surements and analysis; draft of the article; Inas K. Batisha – manuscript revision; research coordination; Lidia Zur - QE measurements and analysis; draft of the article, Alessandro Chiasera – optical spectroscopy and analysis; Maurizio Ferrari and Anna Lukowiak -Research coordi­ nation, manuscript revision. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This research is performed in the framework of the projects ERANetLAC “RECOLA” (2017–2019), and Centro Fermi MiFo (2017–2020). I.K. Battisha. and M.M. Ismaiil acknowledge financial support by the Exec­ utive Programme of Scientific and Technological Cooperation between Arab Republic of Egypt and Italian Republic for the years 2015–2019: entitled; Smart optical nanostructures for green photonics.

Fig. 4. Emission decay curves of the 4F3/2 level for the samples PANKB0.5Nd, PANKB0.75Nd, PANKB1Nd, and PANKB1.5Nd. 5

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