Characterization of Eu- and Y-polytantalate Films Deposited by RF Diode Sputtering
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Characterization of Eu- and Y-polytantalate Films Deposited by RF Diode Sputtering
Vladimir S.Vasilyev, Alvin J. Drehman and Lionel O. Bouthillette Air Force Research Laboratory, Sensors Directorate, 80 Scott Drive, Hanscom AFB, MA 01731 ABSTRACT Using radio frequency (RF) diode sputtering of sintered stoichiometric (Eu,Y)2O3:7Ta2O5 ceramic targets, thin films (0.2-0.6 µm) of Eu- and Y-polytantalates, and their solid solution EuxY1-xTa7O19 were deposited on fused silica, Si (100) and sapphire (001) substrates under various sputtering conditions. As-grown films were amorphous, and were crystallized by postannealing in oxygen at 900 to 1000 oC. The influences of deposition gases (Ar and O2-partial pressure) substrate material, deposition time, substrate temperature, and post-annealing time and temperature on the structural, morphological and photo-luminescence (PL) properties of Eu3+ions in the films have been studied and compared to properties of sintered (Eu,Y)Ta7O19 ceramic and EuTa7O19 single crystals. INTRODUCTION The recent development of photonic devices requires highly efficient and superior stable luminescent materials [1]. One class of such promising materials are the compounds of doubleoxides of RE2O3-Ta2O5 (RE=Rare Earth), that exhibit a fortuitous combination of high thermoand chemical stability with attractive luminescent characteristics. Doped with Eu3+, Tb3+, Tm3+, and Nd3+, RE-tantalates have intensive red-, green-, blue-color and infrared PL and cathodoluminescence (CL) spectra, respectively, with the interesting profile in the rare-earth polytantalates (RE2O3-Ta2O5=1:7) [2–7]. Due to large RE-RE distance (~6-6.5Å) in the RETa7O19 crystalline cell these highly concentrated phosphors do not experience concentration quenching and could produce a further interest for development of multicolor displays, coherent light sources, and high-density optical data storage. These opportunities have created research efforts dedicated to synthesis of ceramics and crystals of rare-earth tantalates and understanding of properties of these materials [7–13]. The challenge of our effort for growing crystal films of Eu- and Y- tantalates is to maintain stoichiometry while providing a uniform large area with excellent properties approaching those of bulk crystals and sintered ceramic. EXPERIMENTAL The films were prepared by RF (13.56 MHz) diode sputtering from each of three sintered targets of stoichiometric mixes of pure grade oxides (EuxY1-xTa7O19, x=1, 0.5 and 0) onto fused silica, Si (100) and sapphire (001) substrates. These substrates were considered to be suitable for photonic devices processing. The conditions for the preparation of films with a high crystallinity and PL intensity were as follows: sputtering voltage 1000 V, sputtering gas composition 5 mtorr Ar + 1 mtorr O2. These conditions were found to supply a typical films deposition ratio 20-50 nm/h. The thickness of obtained films was in the range of several hundred nanometers. The deposition temperature was varied in the range from room temperatur
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