Photo and Cathodoluminescence in Cerium-Activated Yttrium-Aluminium Borates
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Photo- and Cathodoluminescence in Cerium-Activated Yttrium-Aluminium Borates V. Z. Mordkovich Intl Center for Materials Research, KSP East 601, Takatsu-ku, Kawasaki 213-0012, Japan ABSTRACT Ce3+ luminescence in Ce-activated yttrium aluminium borates was studied. Photoluminescnece was excited by continuous-wave UV or by pulse laser irradiation. Cathodoluminescence was excited at the acceleration voltage in the range 5 to 600 V. These phosphors show under continuous wave UV excitation three emission peaks: in near UV, deep blue and light blue ranges. The light blue peak at around 490 nm which may be connected to forbidden 2D3/2 → 2F7/2 transition appears in continuous wave-excited photoluminescence only and does not appear in cathodoluminescence nor under pulse excitation. The blue-emitting Ceactivated yttrium aluminium borates exhibit unusually strong activator ion-host lattice interaction. As a result a substantial red shift in the emission is induced by Ce concentration increase and complicated concentration dependence of the emission intensity is observed. INTRODUCTION Rare earth borate phosphors were first introduced by R.I.Smirnova et al. in 1969 [1] and have been of little or no interest for two decades. More recently due to rising demand for new efficient phosphors for flat panel display applications the rare earth borates’ properties such as high efficiency, easy processibility, durability and often long afterglow have attracted attention. As a result, more publications appeared [2-4]. As for blue-emitting phosphors, they had been represented only by cerium-activated yttrium orthoborate with photo- and cathodoluminescence at ~410 nm i.e. of violet color [1]. Meanwhile, luminescence of Ce3+ is known to be strongly influenced by substituting some yttrium with aluminium [5]. Such substitution may lead to drastic changes in both emission wavelength and in efficiency either due to lower symmetry of Ce3+ ion surrounding or due to different contribution into crystal field by Y3+ and Al3+ ions. We recently introduced a Ce3+-activated yttrium aluminium borate [6] as a blue-emitting phosphor which is more efficient than that of work [1]. The purpose of the present work was to study photo- and cathodoluminescence of the cerium-yttrium-aluminium borates with various Y/Al ratio and Ce3+ concentration. EXPERIMENTAL DETAILS The samples were prepared in the composition range (CexY1-x)1-yAlyBO3 where x=0.008 to 0.5 and y=0 to 0.75. The samples were synthesized at 900°C from stoichiometric amounts of yttrium chloride, cerium chloride and aluminium chloride mixed with excess boron oxide. After washing out the excess boron oxide the final product represents a powder with 2-3 µm particle size. X-ray diffraction showed a distorted hexagonal lattice typical for yttrium borate [7] with parameters slightly varying with Ce or Al concentration change.
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Activation was performed by annealing the samples at the temperature in range 300-1200°C in a flow of a hydrogen/argon gas mixture (hydrogen concentration 10-14 %). Photoluminesc
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