Spectral and Transmittance Properties of Er3+ Doped Zinc Lithium Lead Calcium Borophosphate Glasses

Abstract

Zinc lithium lead calcium borophosphate glasses containing Er3+ in (40-x):P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3:xEr2O3 (where x=1, 1.5,2 mol %) have been prepared by melt-quenching method. The amorphous nature of the glasses was confirmed by x-ray diffraction studies. Optical absorption, Excitation, fluorescence and Transmittance spectra were recorded at room temperature for all glass samples. Judd-Ofelt intensity parameters ?? (?=2, 4, 6) are evaluated from the intensities of various absorption bands of optical absorption spectra. Using these intensity parameters various radiative properties like spontaneous emission probability, branching ratio, radiative life time and stimulated emission cross–section of various emission lines have been evaluated.

Introduction

I. INTRODUCTION

Rare-earth ions-doped luminescent materials have wide range of applications in which white light emitting diodes, solar cells, lasers, infrared to visible up-converters and optical communications. Oxide glasses are the most stable host matrices for practical applications due to their high chemical durability and thermal stability [1-8].Among these hosts, the borophosphate system is attractive due to its superior physical, structural and optical properties compared to pure phosphate or borate system [9-13].The low nonlinear dispersion of the highly rare-earth doped phosphate glasses enables their use in high power applications. Modification of phosphate glass with ZnO had improved glass durability while maintaining low glass transition temperature. Addition of borate in to phosphate glass also increase its durability and created a well-known glass system, namely borophosphate glass.The addition of PbO to the phosphate glass is prediectable to increase the glass stability versus devitrification and the glass becomes chemically inactive,due to the capability of PbO to turn as a modifier with structure units PbO6[14,15  ].Among different rare –earth ions, the Er3+ ion has been identified as the most efficient ion for obtaining the lasing action, frequency up-conversion and optical fiber amplification[ 16-20]. The present work reports on the preparation and characterization of rare earth doped heavy metal oxide (HMO) glass systems for lasing materials. I have studied on the absorption, emission and Transmittance properties of Er3+ doped zinc lithium lead calcium borophosphate glasses. The intensities of the transitions for the rare earth ions have been estimated successfully using the Judd-Ofelt theory, The laser parameters such as radiative probabilities(A),branching ratio (β), radiative life time(τR) and stimulated emission cross section(σp) are evaluated using J.O.intensity parameters( Ωλ, λ=2,4 and 6).

II. EXPERIMENTAL TECHNIQUES

A. Preparation of Glasses    

The following Er3+ doped zinc lithium lead calcium borophosphate glass samples (40-x):P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3: xEr2O3 (where x=1, 1.5.2) have been prepared by melt-quenching method. Analytical reagent grade chemical used in the present study consist of P2O5, ZnO, Li2O,PbO, CaO , B2O3and Er2O3. All weighed chemicals were powdered by using an Agate pestle mortar and mixed thoroughly before each batch (10g) was melted in alumina crucibles in silicon carbide based an electrical furnace.

Silicon Carbide Muffle furnace was heated to working temperature of 10500C, for preparation of zinc lithium lead calcium borophosphate glasses, for two hours to ensure the melt to be free from gases. The melt was stirred several times to ensure homogeneity. For quenching, the melt was quickly poured on the steel plate & was immediately inserted in the muffle furnace for annealing. The steel plate was preheated to1000C.While pouring; the temperature of crucible was also maintained to prevent crystallization. And annealed at temperature of 3500C for 2h to remove thermal strains and stresses. Every time fine powder of cerium oxide was used for polishing the samples. The glass samples so prepared were of good optical quality and were transparent. The chemical compositions of the glasses with the name of samples are summarized in Table 1

Table 1 Chemical composition of the glasses

Sample                                                            Glass composition (mol %)

ZLLCBP (UD)                           40P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3

ZLLCBP (ER 1)                         39P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3:1 Er2O3

ZLLCBP (ER 1.5)      38.5P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3: 1.5 Er2O3

ZLLCBP (ER 2)        38P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3: 2 Er2O3

ZLLCBP (UD)—Represents undoped zinc lithium lead calcium borophosphate glass specimen.

ZLLCBP (ER) -Represents Er 3+ doped   zinc lithium lead calcium borophosphate glass specimens.

III. THEORY

A.  Oscillator Strength

The intensity of spectral lines are expressed in terms of oscillator strengths using the relation    [21].

where, ε (ν) is molar absorption coefficient at a given energy ν (cm-1), to be evaluated from Beer–Lambert law.

Under Gaussian Approximation, using Beer–Lambert law, the observed oscillator strengths of the absorption bands have been experimentally calculated, using the modified relation [22].

where c is the molar concentration of the absorbing ion per unit volume, I is the optical path length, logI0/I is absorbtivity or optical density and Δυ1/2 is half band width.

B. Judd-Ofelt Intensity Parameters

According to Judd [23] and Ofelt [24] theory, independently derived expression for the oscillator strength of the induced forced electric dipole transitions between an initial J manifold ?4fN (S, L) J> level and the terminal J' manifold ?4fN (S' ,L') J' > is given by:   

In the above equation m is the mass of an electron, c is the velocity of light, ν is the wave number of the transition, h is Planck’s constant, n is the refractive index, J and J' are the total angular momentum of the initial and final level respectively, Ωλ (λ = 2, 4 and 6) are known as Judd-Ofelt intensity parameters.

C. Radiative Properties

The Ωλ parameters obtained using the absorption spectral results have been used to predict radiative properties such as spontaneous emission probability (A) and radiative life time (τR), and laser parameters like fluorescence branching ratio (βR) and stimulated emission cross section (σp).

The spontaneous emission probability from initial manifold ?4fN (S', L') J' > to a final manifold ?4fN (S, L) J >| is given by:

IV. RESULT AND DISCUSSION

A. XRD Measurement

Figure 1 presents the XRD pattern of the samples containing show no sharp Bragg’s peak, but only a broad diffuse hump around low angle region. This is the clear indication of amorphous nature with in the resolution limit of XRD instrument.

B. Transmittance Spectrum

The Transmittance spectrum of Er3+doped in zinc lithium lead calcium borophosphate glass is shown in Figure 2.

C. Absorption Spectra                                                                                                                                        

The absorption spectra of ZLLCBP ER (01) glass, consists of absorption bands corresponding to the absorptions from the ground state 4I15/2 of Er3+ ions. Ten absorption bands have been observed from the ground state 4I15/2 to excited states 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, 4F7/2, 4F5/2, 4F3/2, 2H9/2 and 4G11/2 for Er3+ doped ZLLCBP ER (01) glass.

The experimental and calculated oscillator strengths for Er3+ ions in zinc lithium lead calcium borophosphate glasses are given in Table 2

Table 2. Measured and calculated oscillator strength (Pm × 10+6) of Er3+ ions in ZLLCBP glasses.

The various energy interaction parameters like Slater-Condon parameters Fk (k=2, 4, 6), Lande′ parameter ξ4f and Racah parameters Ek (k=1, 2, 3) have been computed using partial regression method .  The ratio of Racah parameters E1/E3 and E2/E3 are about 10.35 and 0.049 respectively. Computed values of Slater-Condon, Lande′, Racah, nephelauexetic ratio and bonding parameter for Er3+ doped ZLLCBP glass specimens are given in Table 3.

Table3. Computed values of Slater-Condon, Lande′, Racah, nephelauexetic ratio and bonding parameter for Er3+ doped ZLLCBP glass specimens.

Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6) were calculated by using the fitting approximation of the experimental oscillator strengths to the calculated oscillator strengths with respect to their electric dipole contributions. In the present case the three Ωλ parameters follow the trend Ω4 < Ω2 < Ω6.

The values of Judd-Ofelt intensity parameters are given in Table 4.

Table 4. Judd-Ofelt intensity parameters for Er3+ doped ZLLCBP glass specimens.

D.  Excitation Spectrum

The Excitation spectra of Er3+doped ZLLCBP glass specimens have been presented in Figure 4 in terms of Excitation Intensity versus wavelength. The excitation spectrum was recorded in the spectral region 300–600 nm fluorescence at 550nm having different excitation band centered at 350,365, 381, 425, 450, 470and 515 nm are attributed to the 2K15/2, 4G9/2, 4G11/2, 2G9/2, 4F3/2, 4F5/2 and 2H11/2 transitions, respectively. The highest absorption level is 4G11/2and is at 381nm.So this is to be chosen for excitation wavelength.

E.  Fluorescence Spectrum

The fluorescence spectrum of Er3+doped in zinc lithium lead calcium borophosphate glass is shown in Figure 5. There are six broad bands (4F7/2→4I15/2), (2H11/2→4I15/2),(4S3/2→4I15/2),(4F9/2→4I15/2),(4I11/2→4I15/2)and(4I13/2→4I15/2)respectively for glass specimens.  

Table 5. Emission peak wave lengths (λp), radiative transition probability (Arad), branching ratio (βR), stimulated emission crosssection (σp), and radiative life time (τ) for various transitions in Er3+ doped ZLLCBP glasses.

Conclusion

In the present study, the glass samples of composition (40-x):P2O5:10ZnO:10Li2O:10PbO:10CaO:20B2O3:xEr2O3 (where x =1, 1.5, 2 mol %) have been prepared by melt-quenching method. The value of stimulated emission cross-section (?p) is found to be maximum for the transition (4I13/2?4I15/2) for glass ZLLCBP (ER 01), suggesting that glass ZLLCBP (ER 01) is better compared to the other two glass systems ZLLCBP (ER1.5) and ZLLCBP (ER02).

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