Fabrication And Properties Of Rare Earth Ions Doped CaF₂ Transparent Ceramics

The development of laser with different wavelengths is one of the hottest research directions of modern laser technology.Lasers with different wavelengths are facing different application fields,such as visible light laser is used in display,lithography and other fields because of its excellent color rendering ability;1?m laser can achieve high power and large energy laser output and it is widely used in industrial processing,laser weapons and other fields;1.5?m laser is in the safe band of human eyes and it is often used in laser communication field;2?m laser has strong cutting ability to human tissues and is an excellent laser light source for medical surgery.The calcium fluoride?CaF₂?material has excellent properties such as wide light transmission range,low phonon energy,and low refractive index,while the rich symmetrical character-site structure in trivalent rare earth ions(RE³⁺)doped CaF₂ endow RE:CaF₂ with very wide absorption and emission bands,which makes RE:CaF₂ materials suitable for application in the field of tunable lasers.The current research on RE:CaF₂ is mainly focused on single crystals,but RE:CaF₂ single crystals have low laser damage threshold and cannot achieve high concentration and uniform doping of RE³⁺ions.RE:CaF₂ transparent ceramics can make up for these deficiencies very well.In this paper,1at.%Nd:CaF₂,1at.%Er:CaF₂,2at.%Ho:CaF₂,4at.%Tm:CaF₂ and Yb:CaF₂ with different doping concentrations nano-powders were synthesized by the co-precipitation method.Then the fabrication and properties of RE:CaF₂ transparent ceramics applied to 1?m,1.5?m and 2?m lasers were studied:?1?1at.%Nd:CaF₂,1at.%Er:CaF₂,2at.%Ho:CaF₂,4at.%Tm:CaF₂ and Yb:CaF₂with different doping concentrations nano-powders were synthesized by the co-precipitation method.The average particle sizes of the Nd:CaF₂,Er:CaF₂,Ho:CaF₂ and Tm:CaF₂ powders were 57 nm,60 nm,54 nm and 44 nm respectively.The average particle size of Yb:CaF₂ powders decreases gradually with the increase of Yb³⁺concentration.All RE:CaF₂ powders were pure CaF₂ phase.?2?1 at.%Nd:CaF₂,1at.%Er:CaF₂,2 at.%Ho:CaF₂ and 4at.%Tm:CaF₂ transparent ceramics were fabricated by air sintering and HIP post-treatment.The effects of pre-sintering temperature on the densification,microstructure and optical quality of the ceramics before and after HIP were studied.The results show that 1at.%Nd:CaF₂transparent ceramics have the best in-line transmittance at pre-sintering temperature of625^oC,reaching 85.0%at 1200 nm.1at.%Er:CaF₂ transparent ceramics have the best in-line transmittance at pre-sintering temperature of 625^oC,reaching 90.2%at 1300 nm.4at.%Tm:CaF₂ transparent ceramics have the best in-line transmittance at pre-sintering temperature of 625^oC,reaching 88.0%at 1400 nm.2at.%Ho:CaF₂ transparent ceramics have the best in-line transmittance at pre-sintering temperature of 600^oC,reaching 92.6%at 1300 nm,which is close to the theoretical value.?3?The absorption spectra of 1 at.%Nd:CaF₂,1 at.%Er:CaF₂ and 4 at.%Tm:CaF₂transparent ceramics were studied.The absorption cross section at 792 nm of1at.%Nd:CaF₂ transparent ceramics is 0.74×10^-20 cm².The absorption cross section at1530 nm of 1at.%Er:CaF₂ transparent ceramics is 0.37×10^-20 cm².The absorption cross section at 676 nm of 4at.%Tm:CaF₂ transparent ceramics is 0.43×10^-20 cm².Then the spectral characteristic of 2at.%Ho:CaF₂ transparent ceramics were studied systematically.The absorption cross section at 1943 nm of 2at.%Ho:CaF₂ transparent ceramics is 0.25×10^-20 cm².The emission cross section at 2031 nm of 2at.%Ho:CaF₂transparent ceramics is 0.39×10^-20 cm².