Emission properties of nanostructured Eu3+ doped zinc aluminate spinels

doi:10.1016/S0925-8388(99)00696-9

Journal of Alloys and Compounds

Volumes 300–301, 12 April 2000, Pages 456-458

https://doi.org/10.1016/S0925-8388(99)00696-9 Get rights and content

Abstract

The preparation of nanostructured ZnAl₂O₄ spinel powders doped with Eu³⁺ ions obtained by a hydrothermal method is described. XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The averaged spinel particle size was determined to be 6 nm as prepared and it increased up to 8 nm for calcination at 500°C. The emission spectra of Eu³⁺ ions measured for the samples calcinated at 500°C demonstrated inhomogeneous shapes characteristic for disordered material which after heating at 1500°C changed shape into an ordered shape characteristic of the crystalline form.

Introduction

Since the discovery by Bhagrava and Galagher [1] that nanosize semiconductors doped with lanthanides demonstrate significant enhancement of radiative transitions, one observes an increasing interest in studies of lanthanide-doped nanocrystalline materials with particle diameters less than 100 nm. Such an effect may find potential applications in designing optoelectronical materials and also as efficient phosphor materials for flat-panel displays. It was found that decreasing nanoparticle sizes increases their emission efficiency in contrast to the microscale powders.

The emission properties of the Eu³⁺-doped γ-Al₂O₃ were reported by Felofilov et al. [2]. The effect of the shape of nanocrystalline particles on emission properties of Eu³⁺ in Al₂O₃ was reported by us [3].

Zinc aluminate ZnAl₂O₄ spinels are widely used as catalytic, ceramic (or glass ceramic) and electronic materials [4], [5], [6]. The optical properties of pure zinc aluminate spinels prepared by the solid state route were reported by Sampath et al. [7], however to our knowledge only the transition metal ion-doped ZnAl₂O₄ spinels were investigated. For instance the optical properties of the Cr³⁺-doped ZnAl₂O₄ spinel obtained by traditional ceramic processing followed by calcination at relatively high temperatures were studied by Nie et al. [8]. No rare-earth-doped zinc aluminate spinels were reported.

Recently, a new method of synthesis of the zinc aluminate spinel has been developed which seems to be very useful for obtaining a nanosize and nanoporous material of a spinel structure with a high surface area [9], [10], [11]. Those properties make them interesting as a host lattice for active systems like rare earth ions.

In this paper we report the emission properties of Eu³⁺ in nanostructured zinc aluminate spinel ZnAl₂O₄ powders.

Section snippets

Synthesis

A nanocrystalline and nanoporous zinc aluminate matrix with high specific surface area and narrow pore size distribution was obtained under hydrothermal conditions. The starting materials for the synthesis were basic aluminium nitrate and hydrated zinc acetate. Basic aluminium nitrate (empirical formula: Al₂(OH)_6−x(NO₃)_x where x was close to 1) was obtained by hydrolysis of powdered aluminium metal in aqueous solution of aluminium nitrate at elevated temperature for some days.

The mixture which

Results and discussion

The emission spectra of nanoparticle ZnAl₂O₄ spinels were measured for samples heated at 500°C. The emission spectra of the powders were measured at room temperature and are shown in Fig. 1, Fig. 2. The assignment of the transition bands is given in the figures.

The spectra of samples heated at 500°C have demonstrated broad bands. A band broadening is typical for disordered systems and is due to multisite distribution. The intensity ratios of the hypersensitive ⁵D₀→⁷F₂ transition band to the ⁵D₀→

Conclusions

Nanocrystalline ZnAl₂O₄ spinels doped with Eu³⁺ ions were prepared by two different doping techniques. The morphology of the obtained nanostructural matrices was studied. The size of the nanocrystallites was determined to be 8 and 15 nm for crystallites heated at 500°C and 1000°C, respectively. It was found that the emission properties of Eu³⁺ were not dependent on the doping techniques. It means that the Eu³⁺ ions are occluded in pores on surfaces of the spinel particles. However a significant

Acknowledgements

This work was performed under a grant from the Polish State Committee for Scientific Research KBN no. 3 TP9B 063 16.

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Emission properties of nanostructured Eu3+ doped zinc aluminate spinels

Abstract

Introduction

Section snippets

Synthesis

Results and discussion

Conclusions

Acknowledgements

J. Lumin.

Spectrochim. Acta

Appl. Catal. A: Gen.

J. Lumin.

Phys. Rev. Lett.

Emission properties of nanostructured Eu³⁺ doped zinc aluminate spinels