Effects of sintering additives on preparation of CaF₂ transparent ceramics

Abstract

The effects of different sintering addictives on the preparation of CaF₂ transparent ceramics were studied. Transparent CaF₂ ceramics were fabricated by vacuum sintering and hot isostatic pressing (HIP) method, using CaF₂ nanopowders synthesized by chemical precipitation method as raw materials. The nanopowders and transparent ceramics were studied using X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and spectrophotometer. The experimental results indicated that the obtained nanopowders presented normal distribution with grain size about 30 nm; transmittance of CaF₂ transparent ceramics was 39% and 26% at 1100 nm for LiF and NaF as sintering addictives, respectively, with corresponding mean grain size 188 μm and 44 μm. Loss of transmission could be attributed to the residual closed porosity. Sintering mechanism was liquid-phase sintering at pre-stage, then solid-phase sintering at later stage, as well as solid solution of lithium ions and sodium ions in the CaF₂ lattice structure.

Keywords

CaF₂ / sintering additives / transparent ceramics / transmittance / solid solution

References

[1] Colmenares C., Shapiro E. G., Barry P. E., . A Europium-Doped, Calcium-fluoride Scintillator System for Low-level Tritium Detection[J]. Nuclear Instruments and Methods, 1974, 114(2): 277-289.

[2] Dressler L., Rsuch R., Reimann R. On the Inhomogenity of Refractive Index of CaF₂ Crystal or High Performance Optic[J]. Crystal Research and Technology, 1992, 27(3): 413-420.

[3] Ko H. J., Chen Y. F., Zhu Z., . Effects of a Low-temperature Buffer Layer on Structural Properties of ZnO Epilayers Grown on (111) CaF₂ by Gwo-step MBE[J]. J. Cryst. Growth, 2000, 208(1–4): 389-394.

[4] Ko H. J., Chen Y. F., Zhu Z., . Photoluminescence Properties of ZnO Epilayers Grown on CaF₂(111) by Plasma Assisted Molecular Beam Epitaxy[J]. Appl. Phys. Lett., 2000, 76(14): 1 905-1 907.

[5] Ma Y., Du G., Wang X., . Growth and Characteristics of ZnO Thin Film on CaF₂ (111) Substrate by Metalorganic Vapor Phase Epitaxy[J]. Applied Surface Science, 2005, 243(1–4): 24-29.

[6] Société CRYSTAL Gmbh.Optische Komponenten: Kalziumfluorid f r UV, VIS und IR-Bereich [DB/DL]. http://www.crystal-gmbh.com/pdf/OPTIK/CAF2.PDF, 2002

[7] Crystran Ltd. Materials Data from Crystran Ltd: Calcium Fluoride [DB/OL]. http://www.crystran.co.uk/uploads/files/96.pdf, 2004

[8] Hatch S. E., Parsons W. F., Weagley R. J. Hot-Pressed Polycrystalline CaF₂:Dy₂₊ Laser[J]. Appl. Phys. Lett., 1964, 5: 153-154.

[9] Bausa L. E., Lifante G., Daran E., . CaF₂:Er³⁺ Molecular Beam Epitaxial Layers as Optical Waveguides[J]. Appl. Phys. Lett., 1996, 68(23): 3 242-3 244.

[10] Lifante G., Balaji T., Munoz-Yague A. Planar Optical Waveguides Fabricated by Molecular Beam Epitaxy of Pb-doped CaF₂ Layers[J]. Appl. Phys. Lett., 1997, 70(16): 2 079-2 081.

[11] Lahoz F., Daran E., Lifante G., . CaF₂:Yb₃ + Pr₃₊ Codoped Waveguides Grown by Molecular Beam Epitaxy for 1.3 μm Applications[J]. Appl. Phys. Lett., 1999, 74(8): 1 060-1 062.

[12] Labbe C., Doualan J. L., Camy P., . The 2.8 μm Laser Properties of Er₃₊ Doped CaF₂ Crystals[J]. Optics Communications, 2002, 209(1–3): 193-199.

[13] Camy P., Doualan J. L., Renard S., . Tm₃₊:CaF₂ for 1.9 μm Laser Operation[J]. Optics Communications, 2004, 236(4–6): 395-402.

[14] Petit V., Doualan J. L., Camy P., . CW and Tunable Laser Operation of Yb₃₊ Doped CaF₂ [J]. Applied Physics B: Lasers and Optics, 2004, 78(6): 681-684.

[15] Su L., Xu J., Xue Y., . Low-threshold Diode-pumped Yb³⁺,Na⁺:CaF₂ self-Q-switched laser[J]. Opt. Express, 2005, 13(15): 5 635-5 640.

[16] Carnall J R. Polycrystalline Bodies and Means for Producing Them[P]. U S:3,476,690, 1969

[17] Ikesue A., Furusato I., Kamata K. Fabrication of Polycrystal line, Transparent YAG Ceramics by a Solid-State Reaction Method[J]. J. Am. Ceram. Soc., 1995, 78(1): 225-228.

[18] Ikesue A., Kinoshita T., Kamata K., . Fabrication and Optical Properties of High-Performance Polycrystalline Nd: YAG Ceramics for Solid-State Lasers[J]. J. Am. Ceram. Soc., 1995, 78(4): 1033-1040.

[19] Kopylov Y. L., Kravchenko V. B., Komarov A. A., . Nd:Y₂O₃ Nanopowders for Laser Ceramics[J]. Opt. Mater., 2007, 29(10): 1 236-1 239.

[20] Zhang J., Wang S., An L., . Infrared to Visible Upconversion Luminescence in Er₃₊:Y₂O₃ Transparent Ceramics[J]. J. Lumines., 2007, 122–123: 8-10.

[21] Aubry P., Bensalah A., Gredin P., . Synthesis and Optical Characterizations of Yb-doped CaF2 Ceramics[J]. Opt Mater., 2009, 31(5): 750-753.

[22] Gerward L., Olsen J. S., Steenstrup S., . X-ray Diffraction Investigations of CaF₂ at High Pressure[J]. Journal of Applied Crystallography, 1992, 25(5): 578-581.

[23] Bensalah A., Mortier M., Patriarche G., . Synthesis and Optical Characterizations of Undoped and Rare-earth-doped CaF₂ Nanoparticles[J]. Journal of Solid State Chemistry, 2006, 179(8): 2 636-2 644.

[24] Scouler W. J., Smakula A. Coloration of Pure and Doped Calcium Fluoride Crystals at 20 °C and −190 °C[J]. Phys. Rev. B, 1960, 120(4): 1 154-1 161.

[25] Ikesue A., Yoshida K., Yamamoto T., . Optical Scattering Centers in Polycrystalline Nd:YAG Laser[J]. J. Am. Ceram. Soc., 1997, 80(6): 1 517-1 522.