Effect of Carbon Doping on F‐Type Defects in YAG and YAG:Ce Crystals

Abstract

Ce‐doped yttrium aluminum garnet (YAG) is among the efficient rare‐earth garnet scintillators and phosphors. Herein, a computational and experimental study of complex F‐type defect centers formed in YAG by doping with cerium and carbon is addressed. The formation energies determined by ab initio calculations of different defects and atomic chemical potentials in YAG:Ce,C are discussed in O‐poor and O‐rich conditions corresponding to the crystal growth under Ar+CO reducing atmosphere, and postgrowth annealing in air, respectively. It is shown that as‐grown crystals contain numerous positively charged defects responsible for F‐type center formation, whereas mainly negative‐charged defects are remained after the annealing in air. The negatively charged defects located nearby Ce luminescence center occupying Y site may stabilize cerium in the tetravalent state and promote a hole transport to this luminescence center. This describes a high scintillation efficiency of Ce,C‐doped garnets. Furthermore, YAG:C and YAG:Ce,C with a high carbon concentration, in addition to luminescence peaked at 400 ns ascribed to F+‐type centers, possess a fast luminescence peaked around 650 nm that may be attributed to the complex defect centers. These unveiled features of the luminescence process in rare‐earth garnets may contribute to the development of efficient luminescence materials.

Influence of Carbon Doping on Stability of Intrinsic Defects in Y3Al5O12 and Lu3Al5O12

“…[4] This concentration exceeds the amount of any intrinsic defects in rare earth garnets.In our recent works, we evaluated the possibilities of carbon incorporation into different crystallographic positions and interstitials, as well as the formation of complex carbon-containing defects in Ce-free (YAG:C) [5] and Ce-doped (YAG:Ce,C) yttrium aluminum garnet. [6] It was determined that the most stable defects are positively charged in crystals grown in the oxygenpoor environment of Ar þ CO, creating conditions for electron capture and formation of color centers. Meanwhile, negatively charged defects were the most stable in the simulation in oxygen-rich conditions, corresponding to annealing in air.…”

“…In this work, by the same methodology, by combining ab initio calculations and optical spectroscopy, [5,6] we evaluated the formation energies and oxidation states of intrinsic and carboninduced defects, as well as optical absorption, photoluminescence (PL) excitation, and luminescence spectra of LuAG:C crystals grown under reducing Ar þ CO atmosphere in W crucibles and annealed in air. [9] The lattice constant was calculated to be 11.87 Å, which agreed well with the experimental value of 11.91 Å.…”

Effects of Codoping With Divalent Cations on Performance of YAG:Ce,C Scintillator

“…They cause deterioration of scintillation performance in Ce 3+ -doped garnets. According to first principles simulations [12,13], VO (oxygen vacancy), CO (carbon occupying oxygen site) and VAl (aluminum vacancy) are the most probable among the isolated defects in as-grown crystals under reducing conditions of CO-containing atmosphere. However, the lowest formation energies are obtained for the CO-VAl4 and Ci-YAl complex defects (VAl4 is an aluminum vacancy in a tetrahedral site; YAl is yttrium occupying Al sites).…”