Laser‐quality Tm:(Lu_0.8Sc_0.2)₂O₃ mixed sesquioxide ceramics shaped by gelcasting of well‐dispersed nanopowders

Abstract

Tm 3+ -doped mixed sesquioxide transparent ceramics are attractive candidates for the generation of robust~2.1 μm lasers. In this paper, laser-quality Tm: (Lu 0.8 Sc 0.2 ) 2 O 3 mixed sesquioxide ceramics were shaped for the first time by gelcasting of well-dispersed nanopowders, which were obtained using a modified coprecipitation method. The dispersibility of starting nanopowders was largely improved using alcohol-water solvent. The rheological properties of slurries were optimized for gelcasting. We also investigated the densification behavior of the gel-casted green compacts. In contrast to the dry-pressing route, it was found that gelcasting could yield more homogeneous and transparent ceramics. The optical in-line transmittance of the ceramic rod 12 mm in length was as high as 80.3% at 2090 nm. Upon pumping the ceramic rod by 796 nm diode laser, a 1.88 W CW laser at 2090 nm was acquired with a slope efficiency of 24.6% (with respect to the input pump power).

Achievements and Future Perspectives of the Trivalent Thulium-Ion-Doped Mixed-Sesquioxide Ceramics for Laser Applications

“…Even though the modern fabrication methods yield disordered ceramic matrices with lasing quality, considerable efforts will be required for obtaining large-sized and large-aperture active components, so as to give an impulse to further development of the advanced 2 μm solid-state lasers required in various fields of science and technology. In this regard, the approach suggested by Wu et al, consisting of gel-casting of well-dispersed nanopowders followed by HIP treatment [ 122 ] for the synthesis of 12 mm long 2 at. % Tm:(Lu 0.8 Sc 0.2 ) 2 O 3 ceramic rods, with an attenuation coefficient of ~0.006 cm −1 at 2090 nm, is a major step towards large, high-optical-quality samples.…”

“…A major challenge in the process of lasing quality mixed-sesquioxide ceramics is the attainment of a pore-free microstructure with homogeneous distribution of chemical components at the nanoscale level, so as to avoid refractive index modulation near grain boundaries. In this regard, two main fabrication methods can be distinguished: The first method consists of a sintering plus HIP approach, with the utilization of commercially available powders or nanoparticles synthesized by co-precipitation and added ZrO 2 as a grain growth inhibitor [ 54 , 121 , 122 ]. The second method involves conventional vacuum sintering of weakly agglomerated nanoparticles produced by laser ablation [ 53 , 112 ].…”

“…Recently, a 2 at. % Tm 3+ :(Lu 0.8 Sc 0.2 ) 2 O 3 was obtained via the gel-casting of well-dispersed nanopowders obtained by co-precipitation method using an alcohol–water solvent, which was expected to yield more homogeneous and transparent ceramics [ 122 ]. The excellent optical quality of samples was carried out from the optical in-line transmittance of a 12 mm long ceramic rod, with results as high as 80.3% at 2090 nm, which is comparable with the theoretical transmittance of ~81.4% at 2090 nm.…”

Fabrication, microstructure and mid-infrared luminescence of Er:(Sc Y1-)2O3 transparent ceramics

“…It helps to greatly reduce the synthesis temperature (typically down to 1800±50 °C), ensures size-scalable production and simplifies the fabrication of highly-doped and especially "mixed" materials with a well-defined composition (i.e., A/B balances) and uniform dopant distribution (as there is almost no segregation of RE 3+ ions as in the case of single-crystals). In the past years, "mixed" sesquioxide transparent ceramics (Lu,Sc)2O3, (Lu,Y)2O3 doped with various rare-earth ions such as Yb 3+ [17][18][19], Tm 3+ [20,21] or Ho 3+ [22] were fabricated. They evidenced smooth and broad emission bands (as compared to the corresponding parent compounds) leading to generation of record-short laser pulses from mode-locked oscillators [4,5].…”

“…This method is of particular interest for solid-solution compositions, as it provides homogeneous mixing of RE-radicals followed by fast crystallization of vapors into nanosized particles having a uniform distribution of chemical elements through their volume [25]. Moreover, high sintering activity of laser-ablated nanopowders enables to achieve full densification of green bodies by conventional vacuum sintering and to avoid costly hot isostatic pressing (HIPing) post-treatment typically used for fabricating "mixed" sesquioxide transparent ceramics with laser quality [20,21].…”