Yoshihiro Nishisu

Optical characterization of spherical fine particles of glassy Eu3+ doped yttrium basic carbonates

Abstract Spherical fine particles of glassy Eu3+ doped yttrium basic carbonate, whose sizes are about 300 nm in diameter, are prepared by a co-precipitation method using urea as a precipitation generator. The optical properties concerned with the f–f transitions of Eu3+ are investigated for the as-prepared powder and the powder samples calcined at 300 and 550 °C. As the calcination temperature becomes high, the absorption band (charge-transfer band) due to the electron transfer from O2− to Eu3+ shifts to lower energy. The forced electric dipole 5 D 0 – 7 F J (J=0,2,3,4) transition strengths and the inhomogeneous width of the 5D0–7F0 luminescence spectrum of Eu3+ increase with calcination temperature. From these results, the local structure around Eu3+ is compared among the three powder samples. The persistent spectral hole burning (PSHB) effect is observed at 10, 70, and 120 K in the 7F0–5D0 transition of Eu3+ in all the samples. It is found that, at these temperatures, the burning reaction rate decreases with increasing calcination temperature. Probable PSHB mechanisms of the three samples are discussed.

Preparation of Spherical Fine Particles of Yttrium/Iron Composite by Precipitation from Homogeneous Solution Containing Urea.

Fine composite particles containing yttrium and iron were prepared from homogeneous solution using urea as a precipitant generator. The ratio of yttrium to iron in the precipitate could be controlled by adjusting the concentration of the starting materials in the initial solution. These composite particles were considered to be amorphous. Shapes and morphology of the precipitated particles were influenced by the difference of the reaction conditions. Particles obtained from the solution containing 1.88 mmol dm-3 FeCl3 H2O, 3.13 mmol dm-3 YCl3 H2O and 500 mmol dm-3 urea at 97 °C were almost spherical and mono-dispersed. Particles precipitated on the condition as mentioned above converted from amorphous into monophasic garnet (Y3Fe5O12) by calcining at 1,200 °C for 5 hours. After calcination, particle changed its color from brown to medium olive and indicated marked magnetic character.