Elsevier

Optical Materials

Volume 36, Issue 9, July 2014, Pages 1463-1470
Optical Materials

Fabrication and enhanced photoluminescence properties of Sm3+-doped ZnO–Al2O3–B2O3–SiO2 glass derived willemite glass–ceramic nanocomposites

https://doi.org/10.1016/j.optmat.2014.03.035Get rights and content

Highlights

  • Sm2O3 doped willemite (Zn2SiO4) glass–ceramics was prepared by melt-quenched method.

  • Sm3+ ions occupy empty hexagonal channels of willemite crystal with heat-treatment.

  • Up to 14-fold photoluminescence intensity enhancement was achieved.

  • Zn-vacancy induces decrease in refractive index with increase in heat-treatment.

  • These materials are promising for phosphors, solid-state laser and optical devices.

Abstract

The transparent willemite, Zn2SiO4 (ZS) glass–ceramic nanocomposites were prepared from melt-quench derived ZnO–Al2O3–B2O3–SiO2 (ZABS) precursor glass by an isothermal heat-treatment process. The generation of willemite crystal phase, size and morphology with increase in heat-treatment time was examined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 80–120 nm. The decreased refractive index with increase in heat-treatment time attributed to partial replacement of ZnO4 units of willemite nanocrystals by AlO4 units and simultaneous generation of vacancies in the Zn-site. Fourier transform infrared (FTIR) reflection spectroscopy exhibits the structural evolution of willemite glass–ceramics. The photoluminescence spectra of Sm3+ ions exhibit emission transitions of 4G5/2  6HJ (J = 5/2, 7/2, 9/2, 11/2) and its excitation spectra shows an intense absorption band at 402 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 14-fold with crystallization into willemite.

Introduction

Recently, rare earth oxide doped glass and glass–ceramics are attracting great interest in solid state lasers, laser cooling, optical communications, storage, optical devices for the three dimensional color displays and upconverting optical devices [1], [2], [3], [4], [5], [6]. Glasses act as smart hosts for the different rare-earth (RE3+) ions. For this reason planar waveguides and optical fibers can be produced easily with them compared to the crystalline competitors.

The willemite (zinc orthosilicate, Zn2SiO4, ZS) is one of the zinc ore minerals and having the phenakite structure. In Zn2SiO4, all the atoms occupy general position and composed of tetrahedral framework where in zinc and silicon positioned in three different fourfold crystallographic sites: two slightly different zinc sites Zn1 (〈Zn–O〉 1.950 Å) and Zn2 (〈Zn–O〉 1.961 Å), and Si (〈Si–O〉 1.635 Å), so resulting in rhombohedra symmetry with lattice parameters a = b  13.948 Å, and c  9.315 Å [7].

This kind of rigid lattice, with only non-centrosymmetric cationic sites, gives the chance to get special optical properties. For this reason, synthetic willemite is very important and widely used as a phosphor in neon discharge lamps, fluorescent lamps, oscilloscopes, black-and-white/color televisions and many other displays and lighting devices (e.g. with Eu3+, Mn2+, Tb3+, Ce3+ doping) [8], [9], [10], [11], [12], [13], [14]. It is found that this willemite can be used as dielectric ceramics for wireless applications [15]. This kind of crystal containing glass–ceramics is reported by many researchers [16], [17], [18], [19], [20], [21] as well. This glass–ceramics material could be used as potential optical host materials for solid state lasers when they are doped with rare earth ions [22], [23], [24]. To the best of our knowledge the reports on luminescence of RE oxide doped transparent willemite glass–ceramics are very few [25]. Luminescence is very sensitive to variation in the local structure of luminescent species, surrounding host composition and their interaction. Among various rare earth, Sm3+ has emerged as a promising candidate for the optical amplification as it provide strong emission in the visible range (orange–red) in glasses and glass–ceramics with high ZnO content. Moreover, the Sm3+ ion has a number of strong absorption bands where effective pumping sources are available.

In the present work, the preparation of Sm3+-doped novel ZnO–Al2O3–B2O3–SiO2 (ZABS) based glass by melt-quench technique and willemite glass–ceramic nanocomposites by isothermal controlled crystallization of precursor glasses is reported. The crystallization process has been studied by differential thermal calorimetry (DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) reflection spectroscopy. The glass and derived glass–ceramics were characterized by studying their thermal, structural, mechanical and optical properties including visible photoluminescence emissions and excitation. The main advantage of ZnO–Al2O3–B2O3–SiO2 (ZABS) based glass systems compared to normal zinc–alumino–silicate glass systems is that the melting and processing temperature will decrease substantially. This will reduce the cost of production of this glass–ceramics. In view of above fact, the aim of this paper is the fabrication and photoluminescence property study of Sm3+-doped willemite glass–ceramics in ZABS glass system. Another objective is to study of this ZS glass–ceramic nanocomposites’ potentiallity for use in the field of photonics as solid-state laser materials.

Section snippets

Precursor glass preparation

The mother glass having molar composition 60ZnO–5Al2O3–15B2O3–20SiO2 doped with Sm2O3 (0.5 wt% in excess) prepared by conventional melt-quenching method. In this work Sm3+ doped ZnO–Al2O3–B2O3–SiO2 glass is designated as Sm-ZABS-0 h glass. High purity raw materials such as zinc oxide, ZnO (99.9% Sigma–Aldrich, St. Louis, MO, USA); silica, SiO2 (99.8%, Sipur A1 Bremtheler Quartzitwerk, Usingen, Germany); boric acid, H3BO3 (99.5%, Fluka Chemie Gmbh, Buchs, Germany); aluminium oxide, Al2O3 (99%,

Density and thermal properties of precursor glass

The precursor glass is visually transparent, appearing light yellow due to Sm3+ doping. The measured density of the precursor glass is 3.8642 g cm−3 and this high value attributes to the presence of relatively high molecular weight of ZnO used as component of the glass. DSC thermogram was recorded for the precursor glass powder to determine the glass transition (Tg) and crystallization temperatures. The DSC thermogram of the precursor glass is shown in Fig. 1(a). It exhibits two intense

Conclusions

The results of XRD, FESEM and FTIR reflectance spectra evidenced the formation of ZS nano-crystals in the ZABS glass matrix. It is found that the crystallite size obtained from XRD pattern varies in the 80–120 nm. The FESEM micrographs evidence the crystallites are spherical in shapes and they form clusters by joined with each other. The size of the crystallites obtained from FESEM micrographs is about 90 nm for Sm-ZS-30h and 140 nm for Sm-ZS-50h glass–ceramic nanocomposites. The Vickers hardness

Acknowledgements

The authors thank Mr. Kamal Dasgupta, Acting Director and Dr. R. Sen, Head, Glass Division of CSIR–CGCRI for their encouragement to carry out this work. We gratefully acknowledge the financial support of BRNS/DAE under the sanction No. 2011/34/6/BRNS/1567 and the in-house project OLP 0369. We also thankfully acknowledge the XRD and Electron Microscope Sections of this institute for recording XRD patterns and microscopic images respectively.

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