Elsevier

Ceramics International

Volume 39, Issue 8, December 2013, Pages 9613-9617
Ceramics International

Combustion synthesis and spectroscopic charaterisation of LaAlO3 nanophosphors doped Er3+ ions

https://doi.org/10.1016/j.ceramint.2013.05.082Get rights and content

Abstract

Lanthanum aluminate (LaAlO3) nanophosphors doped with erbium were successfully synthesized by a combustion process. The powders were characterized X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence spectroscopy. Pure LaAlO3 phase was obtained at 800 °C heated for 4 h, with an average crystal size, as determined by TEM, of 60 nm. Infrared emission spectra and decay times of main luminescence transitions were measured at room temperature. A strong emission is reported at 1550 nm from the (I13/24I15/24) transition, which intensity depends on the Er concentration.

Introduction

Lanthanum aluminate (LaAlO3) with a perovskite-type structure has at room temperature a rhombohedral structure with R-3c symmetry and it undergoes phase transition into the Pm-3 m cubic phase at Tc=527 °C [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]. But this method suffers from many inherent shortcomings, such as the high-temperature heat treatment which has a detrimental effect on the grain size.

Recently LaAlO3 has been successfully prepared by a novel two-step process [4] and microwave irradiation [5]. Moreover, various wet and soft chemical methods including the 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 polyvinyl 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:Er3+ phosphors prepared by combustion synthesis [20], [21], which has the advantage of being simple, fast and economical in doping. The structural details and the optical properties of the synthesized phosphors have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and fluorescence spectroscopy. The photoluminescence emission and excitation as well as the decay times were measured.

Section snippets

Experimental procedure

The starting materials were lanthanum nitrate hexahydrate [La(NO3)3·6H2O] (98%), aluminum nitrate nonahydrate [Al(NO3)3·9H2O] (99%), erbium(III) nitrate pentahydrate [Er(NO3)3·5H2O], and glycine [H2NCH2COOH] (99%). La(NO3)3·6H2O and Al(NO3)3·9H2O Er(NO3)3·5H2O and H2NCH2COOH were dissolved in distilled water. Er3+ ions doped lanthanum aluminate with general formula (La1−xErx)AlO3 were prepared with different concentrations of Er (x=2%, 5%, 10%). During the process, the molar ratio of glycine to

Experimental

The X-ray powder diffraction (XRD) patterns of all the samples were recorded on a Philips X’Pert system (PW3020 vertical goniometer and PW3710 MPD control unit) with CuKα1,2 radiation (λ1=1.54059 Å and λ2=1.54442 A°). 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 scanning electron images of samples were recorded with scanning electron microscope (SEM) JEOL JSM-5600LV, operated at 20 kV equipped with an Oxford

X-ray diffraction

The X-ray diffraction patterns of LaAlO3:Er3+ are shown in Fig. 1. According to XRD analysis (Fig. 1), the LaAlO3 obtained at 800 °C crystallizes in a pure rhombohedral perovskite structure (JCPDS no. 01-082-0478) with space group R-3c (No.167), with unit cell dimensions a=5.37 Å and c=13.10 Å.

So all diffraction peaks in these XRD patterns could be attributed to the rhombohedral perovskite crystal structure of LaAlO3 witch confirm that the doping concentration does not influence the crystalline

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 a particle size of about 60 nm. A strong luminescence at 1550 nm in the infrared (IR) region due to the (I13/24I15/24) transition has been observed in LaAlO3:Er3+ phosphors. This intensity increases up to 5% of Er3+ ions in the sample, and then it decreases because of concentration quenching.

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Foundation item: Project supported by the Ministry of Higher Education, Scientific Research and Technology of Tunisia.

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