Abstract
Ce doped yttrium aluminum garnet (Ce:YAG) is an important photonic material that is used as a yellow phosphor for white light emitting diodes. In this work, the physical and optical properties of Ce:YAG nanophosphors are investigated and the effects of high-temperature thermal treatments and annealing atmospheres on the particle size and luminescence intensity are discussed. Furthermore, photo-luminescence (PL) was measured as a function of temperature and compared with PL from Ce:YAG single crystals and transparent ceramics to understand the mechanism of luminescence decay with temperature. While the characteristics of PL emission as a function of temperature for single crystals and NPs are similar and follow common decay trends, Ce:YAG transparent ceramics exhibit an interesting unusual increase in PL with temperature. We explained this unique novel behavior by a 4-step mechanism involving localized states in the band gap, and provided evidence from thermo-luminescence measurements to support this interpretation. The work reveals a new luminescence phenomenon arising from the overlap of PL and TL emissions; this phenomenon is most likely characteristic of transparent ceramics.
Highlights
Yttrium Aluminum Garnet, Y3Al5O12 (YAG) has been the subject of intense research efforts because of their wide use as detectors, laser host materials and phosphors [1,2,3,4,5,6,7]
In the current work we investigate the physical and optical properties of Cerium-doped YAG (Ce):YAG NPs prepared by the sol gel method including particle size and photoluminescence, and the corresponding effects of annealing temperature and environment as well as compare NP emission with that of Ce:YAG transparent ceramics and single crystals and investigate their luminescent decay with temperature
The formation of pure YAG phase is first seen at 1000°C, when the sample was annealed in the range of 600 to 900°C, X-ray diffraction (XRD) pattern revealed the absence of YAG phase
Summary
Yttrium Aluminum Garnet, Y3Al5O12 (YAG) has been the subject of intense research efforts because of their wide use as detectors, laser host materials and phosphors [1,2,3,4,5,6,7]. Solid state methods induce high levels of defects which affect the optical properties and exciton dynamics Wet chemical routes such as sol-gel methods have significantly reduced the temperature required for the formation of YAG phase, as well as reduced the mixing temperature which allows for better control of particle size and doping limit [22, 27,28,29,30,31]. In the current work we investigate the physical and optical properties of Ce:YAG NPs prepared by the sol gel method including particle size and photoluminescence, and the corresponding effects of annealing temperature and environment as well as compare NP emission with that of Ce:YAG transparent ceramics and single crystals and investigate their luminescent decay with temperature. We are not aware of any reports on similar phenomenon in PL temperature dependence studies
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