Eu²⁺ Stabilization in YAG Structure: Optical and Electron Paramagnetic Resonance Study

Abstract

A set of Eu-doped Y 3 Al 5 O 12 (YAG) phosphors in the powder form was successfully synthesized by multiple-step solid-state reaction under the reducing Ar:5%H 2 atmosphere. Their physical properties were investigated by means of X-ray diffraction, time-resolved luminescence spectroscopy, and electron paramagnetic resonance (EPR). Special attention was given to wellgrounded confirmation of Eu 2+ occurrence in the YAG structure. Xray diffraction confirmed the presence of a major YAG phase in all samples. The influence of Eu concentration, form of doping (EuS, EuF 2 , or Eu 2 O 3 ) and number/form of annealing steps was studied. Corresponding characteristics were measured and evaluated in a broad temperature range (8−800 K). The correlated measurements showed that the single Eu 2+ ions stabilized in YAG in the yttrium position are responsible for the 440 nm emission. The corresponding lowest energy excitation band is situated at 300 nm, and the radiative lifetime of Eu 2+ emission is about 500 ns. A phenomenological model of excited state dynamics was used to explain the experimentally observed features. Possible practical exploitation of the Eu 2+ center in the YAG host is discussed.

Photo-generated dinuclear {Eu(II)}2 active sites for selective CO2 reduction in a photosensitizing metal-organic framework

“…5b ). These two EPR signals are attributed to paramagnetic Eu 2+ species, because the Eu 3+ ions have no EPR signals, while the Eu 2+ ions are EPR active 41 , 42 . The valence change of the Eu 2 oxo-clusters can be attributed to the photo-induced LMCT process.…”

Garnet-Type Nanophosphors for White LED Lighting

“…Moreover, the control of the oxidation state at the nanoscale is problematic. Indeed, when working with micron-sized powder, typical annealing under controlled atmosphere can be performed to stabilize the oxidation state of the doping ion, as for Ce 3+ -doped YAG (George et al, 2013b) and also in Eu 2+ -doped YAG (Havlák et al, 2016). To obtain NCs, post-annealing should be avoided, making the control of the oxidation state more complex.…”

Study of the luminescence of Eu2+ and Eu3+ states in Ca3Ga2Ge3O12:Eu garnet using synchrotron radiation excitation

“…2b) can be caused by some overlapping of the Eu 2þ emission band with the emission band of defect related centers peaked approximately at 460 nm at RT [12,13] and is assumed to the luminescence of F þ centers [12]. Meanwhile, the Eu 2þ luminescence band Ca 3 Ga 2 Ge 3 O 12 :Eu ceramics and other garnet compounds possesses much wider FWHM of about 1.1 eV [16,17] than that in the case of the emission band of F þ centers with typical FWHM of about 0.3 eV (for instance. see Ref.…”

“…The excitation spectra of the Eu 2þ luminescence in Ca 3 Ga 2 Ge 3 O 12 :Eu ceramics show the two wide bands in the UV range, peaked at 5.04 and 6.05 eV, related to the characteristic 4f-5d transitions of Eu 2þ ions in other garnet states [16,17]. Apart from these bands, the excitation spectra of the Eu 2þ luminescence consist also of the bands at E ex (Eu 2þ ) ¼ 7.64 eV, most probably corresponding to the energy formation of the excitons bound with Eu 2þ ions [21,22].…”

“…4, curves 3-1, respectively). The shortest decay component of the luminescence in τ 1 ¼ 3.6-3.85 ns range can be partly caused by the overlapping of the Eu 2þ luminescence with defect centers, namely F þ centers [17][18][19][20]. Meanwhile, the second component of the luminescence in the 12.8-36.6 ns range are more characteristic to the allowed 4f-5d transitions of Eu 2þ ions in other compounds [16,18].…”