Luminescence of YAG:Ce Phosphors Excited by UV Laser Radiation
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OPTICS AND SPECTROSCOPY LUMINESCENCE OF YAG:Ce PHOSPHORS EXCITED BY UV LASER RADIATION V. M. Lisitsyn,1 V. A. Vaganov,1 L. A. Lisitsyna,2 Zh. T. Karipbayev,3 M. Kemere,4 A. T. Tulegenova,5 Y. Ju,6 and Y. N. Panchenko7
UDC 535.37
Spectral and kinetic characteristics of photoluminescence of commercial YAG:Ce phosphors excited both by laser radiation in the range of 4–6.415 eV and by beams of electrons with energy of 250 keV are investigated. It is shown that electron-hole (e-p) pairs are formed in the matrix by electron beam and upon exposure to laser radiation at 193.3 nm (6.415 eV) as well. All excitation methods initiate the band in the range of 560 nm caused by Ce3+ ions and the UV bands at 320 nm and 360–380 nm. UV luminescence is due to luminescence of intrinsic lattice defects. Possible processes of energy transfer to luminescence centers under optical excitation in the range of 4–6.415 eV are discussed. Keywords: YAG:Ce phosphors, UV laser excitation, UV luminescence.
INTRODUCTION The luminescence in YAG:Ce phosphors is effectively excited by optical radiation at 340 and 460 nm. The excitation energy is transferred to luminescence centers emitting at 560 nm. The energy absorption and subsequent luminescence are caused by transitions from 4f (2F5/2) to 5d (2D5/5) and from 5d(2D3/5) and 5d(2D3/5) to 4f(2F5/2) and 4f(2F7/2) energy levels in a cerium ion, respectively [1]. This effect is widely used in InGaN light-emitting diodes to convert blue radiation of the chip to radiation of the visible range [2–4]. The luminescence at 560 nm in the YAG:Се phosphors and ceramics is also excited by ionizing radiation [5–8]. Therefore, the YAG:Се materials are promising for application as scintillators. Under irradiation, electronic excitations formed in the matrix transfer their energy to the luminescence centers. The luminescence in the YAG:Се materials is also excited by optical radiation in the range of 190–300 nm [9, 10], encompassing the spectral range from the edge of the intrinsic absorption band [7] to the shortwavelength edge of the cerium ion excitation band. This effect is promising for visualization of UV radiation fluxes. Optical excitation in this range stimulates the UV luminescence for which, according to [11–14], the intrinsic defects of the lattice are responsible. Hence, investigations of the UV luminescence will be useful for estimation of the degree of defectiveness of the lattice in the YAG:Се materials and the influence of intrinsic defects on UV excitation energy transfer to the luminescence centers at 560 nm. The energy transfer to the luminescence centers excited by UV radiation, especially by UV laser radiation, has been studied absolutely insufficiently.
1
National Research Tomsk Polytechnic University, Tomsk, Russia, e-mail: [email protected]; [email protected]; Tomsk State University of Architecture and Building, Tomsk, Russia, e-mail: [email protected]; 3L. N. Gumilyov Eurasian University, Nur-Sultan, the Republic of Kazakhstan, e-mail: [email protected]; 4Institute of Solid State Physics, Universit
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