Introduction Calcium fluoride has a lot of attributes, which caused it is very attractive material for laser application. It characterizes a very good transparency in wide range of electromagnetic radiation, from UV to IR.... [ view full abstract ]
Introduction
Calcium fluoride has a lot of attributes, which caused it is very attractive material for laser application. It characterizes a very good transparency in wide range of electromagnetic radiation, from UV to IR. Additionally, calcium fluoride emits a low photon energy, which prevents an overheating during the laser pumping process.
Methods
Samples were obtained by using two commercial powders of calcium fluoride: C1-Sigma-Aldrich with an average particle size of 20 µm and C2-provided by ABCR with an average particle size of 8 µm. Ytterbium fluoride was added to the powder of calcium fluoride as a source of active ions. Specimens were sintered in temperature range 900 - 1350oC in vacuum. Additionally samples were densificated by hot isostatic pressing under conditions: 2000 bar and 1300oC. The microstructure of specimens was observed using electron microscopy. Qualitative phase analysis was carried out with the use of X-ray diffraction method. Absorbance of CaF2 sample was measured by spectrophotometer Varian Cary 500. Fluorescence emission was measured by spectrometer SPEX 270M.
Results
XRD analysis confirmed that both powders contains only cubic phase, fig.1. The differences between materials were noticed during thermogravimetric analysis, fig.2. Powder provided by ABCR has contaminations which were analyzed as residual carbon. On basis of SEM CaF2 sample images it was found that surface was free from macro porosity. On the surface of CaF2 samples with 2%Yb it can be observed occurrence of porosity, fig.3. Fig. 4. shows cooperative optical process in cluster of Yb3+ ions at 504nm. Additionally, we can observe upconversion process 2H11/2---> 4I15/2 at 516 and 526 nm for Er 3+ions, which contaminate of ytterbium fluoride. Luminescence of Yb+ ions are presented at 1030nm.
Discussion
Porosity of calcium fluoride doped Yb ions sample is undesirable for laser materials and further works were focused on elimination of microstructure defects. Basis on fluorescence spectra it can be assumed that ions of ytterbium were incorporated in the crystal lattice of calcium fluoride or ions of calcium were substituted by ytterbium ions.
Acknowledgement
This work was funded by the Polish Ministry of Science and Higher Education.
