Divalent and Trivalent Europium Doped Alumina Waveguides Elaborated by Pulsed Laser Deposition
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Divalent and Trivalent Europium Doped Alumina Waveguides Elaborated by Pulsed Laser Deposition Anne Minardi, Claudine Garapon, Jacques Mugnier, Corinne Champeaux1 Laboratoire de Physico-Chimie des Matériaux Luminescents, CNRS-Université Lyon I 10 rue Ampère, 69622 Villeurbanne Cedex, France 1 Laboratoire de Science des Procédés Céramiques et Traitements de Surface, CNRS-Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France
ABSTRACT
Europium doped alumina Al2O3 optical waveguides were prepared by pulsed laser deposition (PLD) using a KrF laser. The targets were obtained by sintering doped powders synthesized by a sol-gel method. Depending on the oxygen pressure used during the deposition, Eu3+ (for 0.1 mbar) or Eu2+ (for 10-5 mbar) are obtained in the films. Two kinds of Eu2+ ions are present, with a 4f-5d broad excitation band peaking at 330 nm and emission bands located at 490 nm or 585 nm respectively. For Eu3+ doped films, the usual 5D0 to the 7FJ multiplets emission spectra were observed. The emission lines are strongly inhomogeneously broadened. Low temperature site selective fluorescence measurements were achieved in order to correlate the different Eu3+ sites observed with the structure of the films (amorphous or γ crystallized). INTRODUCTION Transition metal ions may easily dope α-Al2O3 and Cr:Al2O3 or Ti:Al2O3 are well-known examples of high performance laser materials. Rare earth ions, which have interesting fluorescence properties too, cannot be introduced into α-alumina by conventional crystal growth methods, due to their large size relative to that of Al3+ ions. Up to now, only rare earth doped transition alumina, such as γ-alumina, have been reported: thin films were prepared by implantation or PLD and monolithes by a sol-gel method[1-3]. Our aim is to elaborate by pulsed laser deposition optical waveguides of rare earth doped alumina and to compare their structural, optical and fluorescence properties with those of samples obtained by the sol-gel method, as powders or waveguiding thin films. Rare earth fluorescence properties may be thus considered either as the objective of this study or as a tool enabling to understand how these ions may be incorporated into alumina matrix. It is the reason why Eu3+, which is a simple structural probe, was first chosen. In a preliminary study, we showed that, in case of europium doping, Eu2+ may be obtained instead of Eu3+, when the film deposition is achieved under vacuum rather than under an oxygen pressure [4]. The aim of this article is to give further details about the spectral and dynamic properties of europium, divalent or trivalent and to try to draw conclusions from the structural point of view.
RESULTS AND DISCUSSION
Europium doped alumina films were obtained by pulsed laser deposition using a KrF excimer laser (λ=248 nm) with a fluence of 3 J/cm2 [5]. The pressure in the ultra high vacuum G3.10.1
deposition chamber was adjusted from 10-6 to 10-1 mbar by oxygen introduction. The silica substrates could be heated by an halogen l
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