The research activity on advanced optical materials for various applications, such as lasers, scintillators, phosphors, is greatly increasing with the availability of sintered polycrystalline ceramics, which present some advantages compared to single crystals (sizes, mechanical strength, overall production cost). Understanding their optical properties requires a detailed investigation of their microstructure, especially regarding the exact location of the required dopants (e.g. rare earth elements such as Ce3+, Nd3+ or Yb3+). The main goal of this lecture is to show how Transmission Electron Microscopy (TEM) useful for characterizing rare earth-doped YAG ceramics which were elaborated in different places (Shanghai Institute of Ceramics, China; Konoshima company, Japan; Faenza, CNR, Italy) from the following new observations:
- Nd3+ and Ce3+ luminescent ions strongly segregate at grain-boundaries [1-2-3],
-Yb3+ ions do not segregate significantly at grain-boundaries ,
-There is a correlation between segregation of rare earth dopants in melt crystal growth and ceramic processing depending on their place in the lanthanide family [5-6],
-High Resolution and chemical spectroscopic nano-analysis results indicate the presence of amorphous and crystalline silicate phases at grains triple junction that could be one of the major scattering sources and the reason of the high optical loss in ceramics ,
-At last, a few comments will be given on our way to detect a single luminescent ion in the YAG host by TEM technique .
Characterization of the distribution of rare earth ions in ceramics is especially important for the interpretation of all optical data in relationship with the real luminescent ion concentration. We will give some possible consequences on the behavior of laser ceramics.
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