Structural and luminescence studies on Er3+/Yb3+ co-doped boro-tellurite glasses

doi:10.1016/j.jallcom.2013.01.190

Journal of Alloys and Compounds

Volume 561, 5 June 2013, Pages 142-150

https://doi.org/10.1016/j.jallcom.2013.01.190 Get rights and content

Abstract

The present work reports structural and optical behaviour of the Er³⁺/Yb³⁺ co-doped boro-tellurite glasses 50TeO₂ + 15H₃BO₃ + (5 − x − y)La₂O₃ + 15MgCO₃ + 15SrCO₃ + xEr₂O₃ + yYb₂O₃ (where x = 1, y = 0, 0.5, 1 and 2 in wt%) studied through Fourier transform infrared (FTIR), Raman, absorption, luminescence, upconversion luminescence and lifetime measurements for green laser applications. The Te single bond OTe, O₃BOBO₃ bond bending vibrations and the fundamental stretching vibration of OH groups are confirmed through FTIR and Raman spectra. Through the absorption spectra, bonding parameters, oscillator strengths and Judd–Ofelt (JO) parameters were calculated and reported. From the luminescence spectra, radiative parameters have been calculated for the $^{2} H_{9 / 2} \to^{4} I_{15 / 2},^{4} S_{3 / 2} \to^{4} I_{15 / 2}$ and $^{4} I_{13 / 2} \to^{4} I_{15 / 2}$ excited state transitions. Upconversion luminescence spectra of the prepared glasses have been recorded and the excited state absorption (ESA) and Energy transfer (ET) processes are discussed. The luminescence decay curves for the $^{4} I_{13 / 2} \to^{4} I_{15 / 2}$ transition of the title glasses under 980 excitation wavelength have also been studied and reported.

Graphical abstract

Energy level diagram of Er³⁺ and Yb³⁺ ions and upconversion mechanisms of Er³⁺/Yb³⁺ doped boro-tellurite glasses under 980 nm excitation.

Highlights

► The intensity of the ⁴I_11/2(Er³⁺) transition increases linearly with Yb³⁺ content. ► Higher oscillator strengths for the ²H_11/2 and ⁴G_11/2 confirm the lower asymmetry. ► Enhancement in upconversion emission is observed through energy transfer from Yb³⁺ to Er³⁺ ion. ► E2YBT glass is suggested for suitable green laser applications.

Introduction

Nowadays rare earth (RE) doped glasses draw much attention due to their practical importance in many fields such as colour display, optical data storage, sensor, lasers and optical amplifiers [1], [2], [3]. Particularly, Er³⁺ doped glasses are the attractive one due to their infrared spectral emission around 1530 nm through the $^{4} I_{13 / 2} \to^{4} I_{15 / 2}$ transition which exhibit extensive applications in wavelength division multiplexing, upconversion laser, waveguide laser, Er³⁺ doped fibre amplifier (EDFA) and full colour solid state displays [2], [4], [5]. Interestingly, the Er³⁺ ion energy level scheme allow many radiative transition to occur for a long excited state lifetime that can be conveniently populated by the absorption of photons in the near-infrared (NIR) region. Further, Er³⁺ ion has the ability to convert infrared light into visible light and sufficiently emits photons in the blue, green and red region of the spectrum efficiently. Recently, many researchers focus on the study of structural and luminescence properties of glass matrices containing Er³⁺ and Yb³⁺ ions [6], [7], [8], [9]. Single Er³⁺ doped glasses exhibit small absorption cross-section causing weak upconversion luminescence [10]. In order to improve the emission intensity of the Er³⁺ ions, Yb³⁺ ion is used as a sensitizer to enhance the pumping absorption and quantum efficiency of the Er³⁺ ions due to the fact that, $^{2} F_{7 / 2} \to^{2} F_{5 / 2}$ transition of the Yb³⁺ ion overlap with the $^{4} F_{15 / 2} \to^{4} F_{11 / 2}$ transition of the Er³⁺ ion [11], [12].

Er³⁺ ion exhibit high absorption cross-section between 800 and 1100 nm, whereas the Yb³⁺ ion exhibit high stimulated emission cross-section and broad absorption band. The upconversion process is significantly affected by the sensitizer combination, pumping wavelength and the conversion passage which increases the optical pumping efficiency because of the efficient energy transfer from sensitizer to the luminescent centre. The excess RE ions in the host matrix reduces the luminescent yield due to concentration quenching, ie., inhibition of photon emission due to fast energy migration between Yb³⁺ ions which lead to luminescence traps. So it is necessary to optimise the concentration of the dopant ion in the host matrices [13], [14]. The choice of the glass host with low phonon energy is also an important factor to enhance the upconversion luminescence and to reduce the multiphonon relaxation.

In order to prepare RE doped low phonon oxide glasses, combination of oxide and tellurite glasses combine the advantages of both the matrices to enhance the optical behaviour. Tellurite glass matrices exhibit low energy vibrating phonons at around 750 cm⁻¹, which inturn decreases the multiphonon cross-relaxation and enhances the quantum efficiency of the $^{4} I_{13 / 2} \to^{4} I_{15 / 2}$ transition of the Er³⁺ ion [15]. Furthermore, tellurium dioxide based glasses are the attractive candidates for the synthesis of new optoelectronic devices, non-linear optical applications, upconversion generation and 1.55 μm broadband amplification devices [16], [17], [18], [19]. Apart from these peculiar properties, TeO₂ possess unique structure and their bond connectivity differs from the conventional glass formers such as B₂O₃, SiO₂, GeO₂ and P₂O₅. An interesting characteristic feature of the borate glass is the appearance of variations in its structural properties namely “boron anomaly”, when alkali or alkaline-earth cations are introduced. The present work reports studies made on synthesis, structural, optical, Near infrared (NIR) emission and upconversion emission on Er³⁺/Yb³⁺ co-doped boro-tellurite glasses.

Section snippets

Experimental

The Er³⁺/Yb³⁺ doped boro-tellurite glasses have been prepared by following conventional melt quenching technique using appropriate amount of high purity analytical grade chemicals (99.99% purity) such as H₃BO₃, TeO₂, La₂O₃, MgCO₃, SrCO₃, Er₂O₃ and Yb₂O₃ from Sigma Aldrich. The following is the sample codes and the chemical composition in wt%. $\begin{matrix} E 0 YBT : 50 {TeO}_{2} + 15 B_{2} O_{3} + 4 {La}_{2} O_{3} + 15 MgO + 15 SrO + 1 {Er}_{2} O_{3} + 0 {Yb}_{2} O_{3} \\ E 0.1 YBT : 50 {TeO}_{2} + 15 B_{2} O_{3} + 3.9 {La}_{2} O_{3} + 15 MgO + 15 SrO + 1 {Er}_{2} O_{3} + 0.1 {Yb}_{2} O_{3} \\ E 1 YBT : 50 {TeO}_{2} + 15 B_{2} O_{3} + 3 {La}_{2} O_{3} + 15 MgO + 15 SrO + 1 {Er}_{2} O_{3} + \end{matrix}$

FTIR spectral studies

The FTIR spectra of the Er³⁺/Yb³⁺ doped boro-tellurite glasses shown in Fig. 1 contain several peaks. The peak assignments corresponding to the IR spectral positions are shown in Table 1. The bands observed in the region 3375–3560 cm⁻¹ are due to the OH stretching vibrations [20], [21]. The peaks observed in the region 2800–2900 cm⁻¹ are due to the characteristic of hydrogen bond in the prepared glasses [22]. The strong bands appear around 1644–1648 cm⁻¹ is attributed to the B single bond O⁻ bond in the

Conclusion

The structural and optical properties of the Er³⁺/Yb³⁺ ions in boro-tellurite glasses have been studied and reported. FTIR and Raman spectral studies reveal the presence of quite significant OH⁻ functional groups, B single bond O bond in BO₃ units, BOB bending linkage vibrations and the symmetric stretching vibration of TeO bonds in the TeO₃ units. The bonding parameter studies suggests that, the Er³⁺/Yb³⁺ ligand bond is of ionic in nature.

The prepared glasses possess lower asymmetry which is confirmed

Acknowledgments

One of the authors Prof. K. Marimuthu would like to thank Defence Research and Development Organisation (DRDO), New Delhi for the sanction of financial support in the form of a major research Projects No. ERIPR/ER/1003841/M/01/1282. Mr. K. Maheshvaran is also thankful to the DRDO for the financial support through Project Fellow in the above project.

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Structural and luminescence studies on Er3+/Yb3+ co-doped boro-tellurite glasses

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Experimental

FTIR spectral studies

Conclusion

Acknowledgments

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Structural and luminescence studies on Er³⁺/Yb³⁺ co-doped boro-tellurite glasses