Elsevier

Optical Materials

Volume 34, Issue 11, September 2012, Pages 1742-1746
Optical Materials

Combustion synthesis and photoluminescence of Eu3+ doped LaAlO3 nanophosphors

https://doi.org/10.1016/j.optmat.2012.04.003Get rights and content

Abstract

Eu3+ doped 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), 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 photoluminescence emission is reported at 616 nm, allowing the use of this material as red phosphor.

Graphical abstract

Eu3+ doped LaAlO3 nanophosphors were successfully synthesized by a combustion process, The powders were characterized by infrared spectroscopy (IR), 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. The photoluminescence of LaAlO3 was related to 4f  4f(5D0  7Fi) (i = 1, 2, 3, 4, 5) transitions of Eu3+ ion, the most intense emission of Eu3+ in LaAlO3 was registered for the transition 5D0  7F2, up to 5% of Eu3+ the intensity decrease because of concentration quenching.

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Highlights

► LaAlO3:Eu3+ nanophosphors were successfully synthesized by a combustion process. ► Pure LaAlO3 phase was obtained at 800 °C (4hours), with an average crystal size of 60 nm. ► The most intense emission of LaAlO3:Eu3+ was registered for the transition 5D0  7F2. ► Up to 5% of Eu3+ doped LaAlO3, the intensity decreases because of concentration quenching.

Introduction

Lanthanum aluminate (LaAlO3) with a perovskite-type structure has attracted great attention in recent years for many applications because of its properties. Indeed, this material presents good thermal stability with high melting point at 2180 °C, which can minimize interfacial dislocations [1], good dielectric properties, high relative permittivity (εr = 23), high quality factor (Q × f  68,000; Q = 1/tan δ; f: measuring frequency and tan δ: dissipation factor) and very small temperature coefficient of resonant frequency (τf = −44 ppm/K) [2]. Traditionally, LaAlO3 has been prepared by conventional solid-state reaction of Al2O3 and La2O3 in the temperature range of 1500–1700 °C [3], [4]. But this typical 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.

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 [5], sol–gel process [6], [7], [8], EDTA gel route [9], [10], co-precipitation method [11], [12], pyrolysis using triethanolamine [13] and combustion synthesis with urea as fuel [14], [15].

Moreover, various wet and soft chemical methods including polymerized complex method using citric acid and ethylene glycol route have been reported [16]. Recently LaAlO3 have been successfully prepared by microwave irradiation [17].

This paper presents the synthesis and characterization of LaAlO3:Eu3+ phosphors, prepared by combustion synthesis, 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), 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 [Eu(NO3)3·5H2O], and glycine [H2NCH2COOH] (99%). La(NO3)3·6H2O and Al(NO3)3·9H2O Eu(NO3)3·5H2O and H2NCH2COOH were dissolved in distilled water. Eu3+ ions doped Lanthanum aluminate with general formula (La1−x Eux) AlO3 were prepared with different concentration of Eu (x = 2%, 5%, 10%). During the process, the molar ratio of glycine

Experimental

The X-ray powder diffraction (XRD) patterns of all samples were recorded on a X’PERT Pro PANAnalytical diffractometer with Cu Kα radiation (λ = 1.5418 Å). Infrared spectra were recorded on a NICOLET 560 spectrometer using KBr pellets in the region of 4000–400 cm−1.

The scanning electron images of samples were recorded with scanning electron microscope (SEM) JEOL JSM-5600LV, operated at 20 kV equipped with an Oxford Instruments ISIS series 300 EDS detector.

The morphology of products was characterized

X-ray diffraction

The X-ray diffraction patterns of LaAlO3:Eu3+ are shown in Fig. 1. According to XRD analysis (Fig. 1a), a pure rhombohedral phase of LaAlO3 (JCPDS no. 01-082-0478) with a perovskite structure could be obtained at 800 °C. Fig. 1b shows that the doping concentration does not influence the crystalline phase formation. So all diffraction peaks in these XRD patterns could be attributed to the rhombohedral perovskite crystal structure of LaAlO3 with space group R-3c, with unit cell dimensions a = 5.369 Å

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 4f  4f(5D0  7Fi) (i = 1, 2, 3, 4, 5) transitions of Eu3+ ion, the most intense emission of Eu3+ in LaAlO3 was registered for the transition 5D0  7F2, up to 5% of Eu3+ the intensity decrease because of concentration quenching.

Acknowledgement

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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