Ce and La Single- and Double-Substitutional Defects in Yttrium Aluminum Garnet: First-Principles Study

Abstract

The atomistic structure, energetics, and electronic structure of single substitutional Ce and La defects and double substitutional Ce-La defects in Ce,La-codoped yttrium aluminum garnet (YAG) Y 3 Al 5 O 12 have been studied by means of first-principles periodic boundary conditions density-functional theory calculations. Single substitution of Y by Ce or by La produces atomistic expansions around the impurities which are significantly smaller than the ionic radii mismatches and the overall lattice distortions are found to be confined within their second coordination spheres.In double substitutional defects, the impurities tend to be as close as possible. La-codoping Ce:YAG provokes an anisotropic expansion around Ce defects. The Ce impurity introduces 4f occupied states in the 5.0 eV computed gap of YAG, peaking 0.25 eV above the top of the valence band, and empty 4f , 5d, and 6s states starting at 3.8 eV in the gap and spreading over the conduction band.La-codoping produces very small effects on the electronic structure of Ce:YAG, the most visible one being the decrease of covalent bonding with one of the oxygen atoms, which shifts 0.05Å away from Ce and gets 0.04Å closer to La in the most stable Ce-La double substitutional defect.

Multicenters in Ce3+ visible emission of YAG ceramics

“…Since Ce 3+ has in 8-fold coordination larger ionic radius compared to Y 3+ [28], in Ce:YAG crystal a significant expansion of the distorted cubic local structure (limited to the nearest neighbors coordination O 2À sphere) takes place. The estimated two Ce 3+ -O 2À distances, 2.38 Å and 2.52 Å [27], are much larger than those of Y 3+ -O 2À 2.31 Å and 2.44 Å in pure YAG, and the expansion is anisotropic; these experimental results are in agreement with the theoretical estimation of structure relaxation near Ce 3+ in YAG [29]. The symmetry of Ce 3þ Y center can be considered as D 2d , the parent group of D 2 , as the pressure data show [30].…”

Local structure of the Ce3+ ion in the yellow emitting phosphor YAG:Ce

“…Despite the fact that this phosphor material was proposed almost 45 years ago [1], and that it has been very thoroughly investigated from the point of view of optical spectroscopy [2][3][4][5][6] and electronic structure [6,7], to the best of our knowledge an experimental investigation of the local structure of the impurity in the garnet structure has never been reported so far. For this reason, we have found it interesting to undertake a detailed study of the location of the Ce3+ ions in YAG using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, with the aim of gaining more insight on the spectroscopic behaviour of this valuable material, and to compare the experimental results with the theoretical ones [7,8]. We are also confident that the present structural results will allow a solid foundation for future improved electronic structure calculation on YAG:Ce.…”

Transition of Emission Colours as a Consequence of Heat-Treatment of Carbon Coated Ce3+-Doped YAG Phosphors

“…Especially, white light can be generated through a simple combination of blue-emitting devices and yellow emitting phosphor YAG:Ce 3+ , i.e., phosphor-converted LEDs (PC-LEDs), which have been successfully commercialized [9]. Therefore, adjusting luminescence properties of YAG:Ce 3+ attract much attention via codoping with another lanthanide ions (La 3+ , Pr 3+ , Tb 3+ , Sm 3+ codoping) [10,11,12,13,14] or modification of the host-lattice by substitution (Lu/Y, Ga/Al, Si/Al, N/O, Si-N/Al-O) [15,16,17,18,19,20]. …”