Temperature induced conversion from surface to bulk sites in Eu 3-impregnated CeO 2 nanocrystals

• Evolution with calcination temperature of Eu 3 sites in CeO 2 nanocrystals is investigated by time-resolved photoluminescence spectroscopy. In the as-synthesized Eu 3 impregnated CeO 2, most of Eu 3 ions reside on surface (S) sites. The Eu 3emission in S sites is broad and short-lived (Ï„ 240 ÎŒs) being dominated by the electric dipole (ED) 5D 0- 7F 2 emission with little evidence for clustering. After calcination (between 500 and 1300 °C), Eu 3 is distributed on surface, cubic and up to three additional crystalline sites. Surface type emission could be detected until 1100 °C. In cubic sites, Eu 3 substitute for the lattice Ce 4 with O h symmetry (O sites). The emission of Eu 3 in O sites is characterized by relative long-lived (Ï„ 1.8-2 ms) and ultra-narrow (FWHM 7 cm -1) magnetic dipole (MD) 5D 0- 7F 1 emission centered at ∌591 nm. Three more crystalline sites are attributed to the oxygen vacancy charge-compensated defects: trigonal with C 3v symmetry (C1 sites) and C2 and C3 sites with C 2v or lower symmetry. Eu 3 in C1 sites exhibits predominant ED 5D 0- 7F 2 emission centered at ∌610 and 632 nm with lifetime of 0.85-1 ms. The C1 sites are assigned to Eu 3-(oxygen vacancy)-associated cubic sites. The O 2- to Ce 4 electronic charge-transfer band sensitizes preferentially the Eu 3 emission in O and, to a less extent, C1 sites but not the S sites. Overall, the results show that the oxygen vacancies are distributed around both Eu 3 and Ce 4 and the Eu 3-oxygen vacancy interaction mode as nearest-neighbour or next-nearest-neighbour depends on the calcination temperature.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

Calcination temperature

Charge-transfer bands

Electric dipole

Interaction modes

Magnetic dipole

Nearest-neighbour

Temperature-induced

Time-resolved photoluminescence spectroscopy

Calcination

Charge transfer

Crystalline materials

Nanocrystals

Oxygen vacancies

Photoluminescence spectroscopy

Europium

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