Wydarzenia

Seminarium Oddziału Spektroskopii Optycznej

Fabrication aspects of coarse and nanograined optical ceramics

dr Roman P. Yavetskiy

Institute for Single Crystals of NAS of Ukraine, Kharkov, Ukraine

The approach to produce Y₂O₃:Eu³⁺ nanograined ceramics by the transformation-assisted consolidation of 125 nm discrete monodispersed nanospheres under high pressures will be described [1]. Compared to coarser analogues nanograined ceramics has improved mechanical properties (due to significant contribution of grain boundaries) and potentially better optical properties (due to lower light scattering on defects with dimension below the visible light wavelengths) [2]. Nanograined ceramics was fabricated via high-pressure (7.7 GPa) low-temperature (~0.1T_m) sintering in toroidal-type high-pressure apparatus. Y₂O₃:Eu³⁺ polycrystalline nanospheres (~40 nm crystallite size) prepared by co-precipitation method were used as a starting material. The phase composition evolution, morphologies, densities, luminescent and mechanical properties of sintered ceramics vs. preparation conditions will be presented.

Optically-transparent (T=50 %) bulk nanograined Y₂O₃:Eu³⁺ ceramics with relative density of 99±1 % and average grain size in the 10-40 nm range have been produced by high-pressure low-temperature sintering. Optical Y₂O₃:Eu³⁺ nanograined ceramics consists of mixture of cubic (C) and monoclinic (B) phases depending on the P-T sintering conditions. Transformation-assisted consolidation allows one to fabricate Y₂O₃ nanoceramics with average grain size three times smaller (12 nm) than that of starting nanopowders (37 nm) at unprecedented low temperature due to significant activation of plastic flow during phase transformation. Mechanical properties of sintered ceramic will be presented. Luminescence of nanograined Y₂O₃:Eu³⁺ ceramics will be analyzed as a spectral probe to identify its crystal structure.

Peculiarities of phase formation and densification processes during reactive sintering of Nd³⁺:YAG laser ceramics prepared using particles with different size have been studied. It has been found that utilization of submicron powders can significantly reduce YAG formation temperature from 1700°C for coarse powder to 1200-1500°C for fine powders. Moreover, utilization of different-sized yttria and alumina particles provide a competitive advantage of shrinkage over expansion processes by changing the kinetics of YAG phase formation. Nd³⁺:YAG (1-4 at.%) laser ceramics with in-line optical transmission of about 82.5 % at l=1064 nm has been produced by reactive sintering. Finally, we succeed in lasing of Nd³⁺:YAG (4 at. %) ceramics under laser diode pumping.