Rare earth dopant

Examination of the electronic states of catalysts and of rare earth dopants in phosphors are other applications which come to mind. When more is known about some of the yet unexplored properties of other possible Mossbauer nuclides, Mossbauer spectroscopy bids fair to being a powerful tool in rare earth chemistry. 

The materials used as up-converters consist of a rigid host lattice with rare earth dopants. Fluorides and oxides have been used as host lattices, the latter being slightly... 

These include ion-ion energy transfer, which can give rise to concentration quenching and non-exponential decay and relaxation by multiphonon emission, which is usually essential for completing the overall scheme, and can affect the quantum efficiency. For low concentration of rare earth dopant ions the principle nonradiative decay mechanism is a multiphonon emission. 

A simple analysis would predict that the conductivity should be a maximum when half the oxygen lattice sites are vacant however, this is not the case. In Figure 14, the effect of various rare earth dopants on the properties of CeCh show that the ionic conductivity is highly dependent on the ionic radius of the dopant. Moreover, the conductivity increases and then decreases across the rare earth dopant series from Yb to Ta, peaking at Gd (Figure 14). A similar observation has been made for Zr, with the peak occurring at Sc. It is clear that the conductivity drops with relatively modest additions of the rare earth ion, when the vacancy concentration is only a few percent. 

The tetragonal RE, Y, and Sc orthophosphates in particular have been widely used as host media for a variety of solid state chemical, spectroscopic, magnetic resonance, neutron and other studies of rare-earth and actinide impurities. These materials have proved to be ideal hosts for the incorporation of other rare-earth dopants (e.g., Er-doped Lu(P04) for microlaser studies). Doped orthophosphates with desired levels of dopants are desirable for both basic investigations and applications. Unfortunately, there are apparently no available quantitative data on the segregation coefficients for the rare earths in the tetragonal orthophosphates. 

The composition of the IGF may vary across its width. In Figure 14.27, the rare-earth dopant has formed an La-rich monolayer at the glass/crystal interface. 

Thompson, A.M., K.K. Soni, H.M. Chan, M.P. Harmer, D.B. Williams, J.M. Chabala, and R. Levi-Setti. 1997a. Rare earth dopant distributions in creep-resistant alumina. Journal of the American Ceramic Society 80(2) 373-376. ... 

Chani VI, Boulon G, Zhao W, Yanagida T, Yoshikawa A (2010) Correlation between segregation of rare earth dopants in melt crystal growth and ceramic processing for optical applications. Jpn J Appl Phys 49 075601... 

Figure 1.24 Dependence of room temperature fracture strength of doped Ce02 ceramics on the concentration of rare earth-dopants yttrium (YDC), gadolinium (GDC), and samarium (SDC).[272],...

Ersundu, A.E., Karaduman, G., Gelikbilek, M., Solak, N. Aydin, S. (2010). Effect of rare-earth dopants on the thermal behavior of tungsten-tellurite glasses. Journal of Alloys and Compounds, 508, pp. 266-272,0925-8838... 

The position and value of the minimum of the activation energy H. as a function of rare-earth dopant content appears to vary with dopant type. In fact the minimum value of the activation energy H, rnin shows a smooth parabolic-type dependence with the ionic radii of the dopant, exhibiting a minimum in the region between Gd (1.053 A) and Nd (1.109 lown in the inset of... 

Extensive atomistic simulation work " has provided valuable insights into the nature of defect association and migration. It is generally recognized that both attractive coulombic interactions and attractive or repulsive elastic lattice relaxation play a major role in the energetics of ionic transport. The atomistic simulations conclude that for small dopants, the oxide ion vacancies preferentially associate with dopant ions, whereas for large dopants the oxide ion vacancies tend to associate with Ge host cations. The switchover is estimated to occur at a rare-earth dopant ionic radius similar to that of Gd, which offers a rational for the minimum in activation energy and the maximum in ionic conductivity observed for Gd- or Sm-doped Andersson et con-... 

F. Goutaland, P. Jander, W. S. Brocklesby, G. Dai, Crystallisation effects on rare earth dopants in oxyfluoride glass ceramics. Opt. Mater. 22, 383-390 (2003). 

Fig. 4.2 Conductivity and binding energies of rare earth dopants in Ce02 as a function of ionic size...

The addition of rare earths to dielectric materials has been studied for a long time. Rare earth dopants in BaTi03 have been reported to lower the resistivity (Saburi, 1959), while La-doped BaZr03 showed an increase in resistivity by several orders of magnitude (Koenig and Jaffe, 1964). The former was attributed... 

The refractive index of the basic glass compositions is often modified by the addition of rare earth dopants [219,518]. To modify the mechanical and optical properties, occasionally the fibres are crystallised before use [510]. 

---