Studies on Thermal Migration of Eu Ion Doped into TiO₂ Nanoparticles

Abstract

The location of the Eu ion in the TiO 2 lattice was investigated as a function of sintering temperature using X-ray photoelectron spectroscopy (XPS), to clarify the role of the Eu ion in TiO 2 nanoparticles synthesized by the simple sol-gel method. The crystalline structure as well as the average crystallite size were evaluated using X-ray diffraction (XRD), and the direct observation of nanoparticles was carried out using atomic force microscopy (AFM). A model was proposed in which, in the as-synthesized gel state, the Eu ion occupies the core part of a nanoparticle, and with increasing sintering temperature, it migrates toward the particle shell to finally reach the surface at high sintering temperatures above 900 C, at which sufficient thermal energy is provided to allow the Eu ion to migrate to the surface of the nanoparticles, resulting in the formation of Eu 2 Ti 2 O 7 with a pyrochlore structure and an abrupt decrease in the photoluminescence (PL) intensity of the Eu ion.

Spectroscopy Study on the Location and Distribution of Eu3+ Ions in TiO2 Nanoparticles

“…The rutile phase appears at sintering temperatures above 950 C in 1 mol % Eu 3þ -doped titania, while it appears at temperature above 700 C in non-doped titania. 28) This is consistent with our results for Eu500, Eu900, TiO 2 500, and TiO 2 900. Figure 3 shows absorption spectra of Eu500, Eu900, TiO 2 500, and TiO 2 900 nanoparticles at room temperature, all of which are similar to each other.…”

“…It has, however, been observed in X-ray photoelectron spectroscopy (XPS) that the Eu 3þ ions have the tendency to locate near the surface. 28) We tried to find different PL spectra between the two samples. When Eu900 was excited at 290 nm or shorter wavelengths, we observed that a weak broad band spectrum was superposed on a sharp line spectrum as shown in Spectrum (4) of Fig.…”

“…As the sintering temperature is increased, the phase changes from anatase to rutile. 5,28) The critical temperature is different between doped and non-doped titania. The rutile phase appears at sintering temperatures above 950 C in 1 mol % Eu 3þ -doped titania, while it appears at temperature above 700 C in non-doped titania.…”

Lanthanide modified semiconductor photocatalysts

“…At temperatures above 900 1C, the Eu 3+ ions migrate to the surface and form Eu 2 Ti 2 O 7 . 107 The photoluminescence abruptly decreases due to the formation of the pyrochlore structure; this was confirmed in a subsequent study. 108 The luminescent and thermal property of Eu-TiO 2 fiber prepared by electrospinning was studied by Bianco et al The emission spectrum was dominated by the 5 D 0 to 7 F 2 transition and the broadness of the peak suggested an inhomogeneous distribution of the Eu 3+ ion.…”

Spectroscopic Signatures of Sub-Second Laser-Calcined Dy3+-Doped Oxide Precursors for Use in ex Situ Thermal Impulse Sensors

“…Both of these effects can be attributed to the anatase-to-rutile phase transformation, as the lattice volume shrinks during this transformation and causes the Dy 3+ ions to be ejected from lattice sites. These ejected Dy 3+ ions can then result in the formation of a secondary phase, which most likely has poorer PL properties. ,− …”