Plasma spraying of cerium-doped YAG
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Jan Kubát Crytur, Ltd., 511 01 Turnov, Czech Republic
Zdenek Pala and Barbara Nevrlá Institute of Plasma Physics, Academy of Sciences of the Czech Republic, 180 00 Prague 8, Czech Republic (Received 20 March 2014; accepted 21 August 2014)
Yttrium–aluminum garnet doped with Ce was plasma sprayed using two different processes – gas-stabilized plasma torch and water-stabilized plasma torch. Coatings on various substrate materials (stainless steel, ceramics, YAG undoped crystals), as well as self-standing plates, were obtained. The coatings adhered on materials with relatively large variety of thermal expansion coefficient. Besides microstructural, crystallographic, and thermal-stability investigations, numerous optical tests were performed. They included cathodoluminescence (CL), UV-VIS-NIR reflectance, and response of the Ce:YAG on light with various wave lengths. After spraying, the desired YAG crystalline phase sustained without any decomposition, but an amorphous fraction was present in both types of coatings. Selected coatings were heat-treated to crystallize fully and change their optical properties. Minor amorphous fraction crystallized at 930 °C. The heat-treated coatings exhibited higher CL and also larger visible emission when illuminated with a 366 nm lamp. Microhardness of the coatings was tested as well and proved the mechanical similarity of both coating types and difference from the single crystal. The optical responses of the coatings were influenced by imperfections like splat boundaries, pores, and thin cracks, which were healed only partly by heat treatment. However, the Ce:YAG was first plasma sprayed and moreover produced by both spray techniques without an irreversible loss of the desired garnet phase. I. INTRODUCTION
The most important oxide for luminescent applications is yttrium aluminum garnet or YAG with chemical formula Y3Al5O12. Cerium-doped YAG is an important photoluminescence material used in scintillators and for white light production in solid state light emitters. Scintillators are optical materials that emit pulses of visible photons when excited with high energy radiation. Gamma ray spectrometers providing high sensitivity and effective isotope identification require high energy resolution, high effective atomic number and scintillators that can be produced with large sizes.1 Recently, polycrystalline ceramics have been developed to the point where they can compete with the performance of single crystals for light emitting applications.2,3 When Ce:YAG is excited by light in the blue range, it produces yellow light that, when combined with the incident blue light, appears bright white to the human eye. Most work done on Ce:YAG so far has been about single crystals, but
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.251 2344
J. Mater. Res., Vol. 29, No. 19, Oct 14, 2014
http://journals.cambridge.org
Downloaded: 06 Dec 2014
polycrystalline ceramic Ce:YAG has a serious potential for efficient white light production.4 Ceramic single crys
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