Elsevier

Optical Materials

Volume 35, Issue 6, April 2013, Pages 1184-1188
Optical Materials

Combustion synthesis and photoluminescence of Tb3+ doped LaAlO3 nanophosphors

https://doi.org/10.1016/j.optmat.2013.01.013Get rights and content

Abstract

Terbium doped lanthanum aluminate (LaAlO3) nanophosphors were successfully synthesized by a combustion process using concentrated solution of lanthanum nitrates and aluminate as oxidiser, and glycine acid as fuel. The powders were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence spectroscopy. Pure LaAlO3 phase was obtained at 800 °C heated for 4 h, without formation of any intermediate phase, with an average crystal size, as determined by TEM, of 60 nm. Intense green emission is reported at 542 nm, from the 5D4 level, which intensity depends on Tb concentration.

Highlights

► LaAlO3:Tb3+ nanophosphors were successfully synthesized by a combustion process. ► Pure LaAlO3 phase was obtained at 800 °C (4 h), with an average crystal size of 60 nm. ► The most intense emission of Tb3+ in LaAlO3 was registered for the transition (5D47F5) at 542 nm. ► Up to 10% of Tb3+ doped LaAlO3, the luminescence intensity decreases because of concentration quenching.

Introduction

Lanthanum aluminate (LaAlO3) with a perovskite-type structure presents good thermal stability with high melting point at 2180 °C, which can minimize interfacial dislocations [1]. Typically, LaAlO3 has been prepared by conventional solid-state reaction of Al2O3 and La2O3 in the temperature range of 1500–1700 °C [2], [3], [4]. But this method suffers from many inherent shortcomings, such as the high-temperature heat treatment which have a detrimental effect of the grain size, limited chemical homogeneity and low sintering temperature.

Recently LaAlO3 have been successfully prepared by microwave irradiation [5]. Moreover, various wet and soft chemical methods including polymerized complex method using citric acid and ethylene glycol route have been reported [6]. Several low temperature (750–900 °C) chemical routes are used for preparing finer and homogeneous powders of LaAlO3 like Poly Vinyl Alcohol (PVA) with metal nitrate synthesis [7], sol–gel process [8], [9], [10], EDTA gel route [11], [12], co-precipitation method [13], [14], pyrolysis using triethanolamine [15] and combustion synthesis with urea and hydrazine as fuel [16], [17], [18], [19].

This paper presents the synthesis and characterization of LaAlO3:Tb3+ phosphors, prepared by combustion synthesis [20], which has the advantage of being simple, fast and economical in doping. The structural details and optical properties of the synthesized phosphor have been investigated by X-ray diffraction (XRD), Rietveld refinement, transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared spectrometry (IR) studies, and fluorescence spectroscopy.

Section snippets

Experimental procedure

The starting materials were lanthanum nitrate hexahydrate [La(NO3)3⋅6H2O] (98%), aluminum nitrate nonahydrate [Al(NO3)3⋅9H2O] (99%), europium(III) nitrate pentahydrate [Tb(NO3)3⋅5H2O], and glycine [H2NCH2COOH] (99%). La(NO3)3⋅6H2O and Al(NO3)3⋅9H2O Tb(NO3)3⋅5H2O and H2NCH2COOH were dissolved in distilled water. Tb3+ ions doped Lanthanum aluminate with general formula (La1−x Tbx) AlO3 were prepared with different concentration of Tb (x = 2%, 5%, 10%, 15%, 20%). During the process, the molar ratio

Experimental

The X-ray powder diffraction (XRD) patterns of all samples were recorded on a Philips X’Pert system (PW3020 vertical goniometer and PW3710 MPD control unit) with Cu Kα 1, 2 radiation (λ1 = 1.54059 Å and λ2 = 1.54442 Å). In order to improve the signal to noise ratio, at least three runs (collected with 10 s/step and 0.05°/step) were measured.

The quantitative phase analysis for samples composed of one crystal and one amorphous phase (CGXXC series) was performed on XRPD data by applying the Rietveld

X-ray diffraction

The X-ray diffraction patterns of LaAlO3:Tb3+ are shown in Fig. 1. According to observed and calculated XRD analysis (Fig. 1a), the structural analysis of LaAlO3 obtained at 800 °C is carried by Rietveld refinement program. It crystallizes in a pure rhombohedral perovskite structure with space group R-3c (No. 167). The reliability factors obtained from the refinement are Rwp = 8.02, Rp = 5.82, Rexp = 3.58, with unit cell dimensions a = 5.37 Å and c = 13.10 Å. Which are close to the reported values (JCPDS

Conclusion

A pure LaAlO3 with a perovskite structure was obtained at 800 °C using a combustion method. The TEM image shows that we obtain a nanopowder with the particle size about 60 nm. The photoluminescence of LaAlO3 was related to 5D47FJ (J = 6; 5, 4, 3) transitions of Tb3+ ion, the most intense emission of Tb3+ in LaAlO3 was registered for the transition (5D47F5) at 542 nm, up to 10% of Tb3+ the intensity decrease because of concentration quenching.

Acknowledgments

This work is supported by the Ministry of Higher Education and Scientific Research in Tunisia. Mr. Tiziano Finotto, Mr. Loris Bertoldo and Mr. Davide Cristofori are gratefully acknowledged for conducting the XRD measurements and TEM images.

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