Sesquioxide ceramics (Y2O3, Lu2O3 and Sc2O3) along with their solid solutions show great potential as hosts for solid-state laser gain materials due to their great suitability for various rare-earth ions, comparably physical properties to single crystals and far lower preparation temperature than the melting point (above 2400 °C). In this work, the development of the fabrication of rare-earth ions doped-sesquioxide ceramics like synthesis of raw nano-powders and ceramic sintering is reviewed, which demonstrates that the ceramics fabricated by vacuum sintering plus hot isostatic pressing technology from well-dispersive nano-powders possess high transparency with uniform microstructures. And the stable synthesis of powders, optical quality and large-scale preparation of ceramics need further investigation. Meanwhile, the progress on laser performance of the corresponding transparent ceramics is also summarized, which reveals that rare-earth active ions doped sesquioxide ceramics have great potential in efficient high power and ultrashort pulse laser applications during 1∼3 μm.

Research progress and prospects of rare-earth doped sesquioxide laser ceramics

Properties of transparent Re3+: Y2O3 ceramics doped with tetravalent additives

High efficiency emission of a laser based on Yb-doped (Lu,Y)2O3 ceramic

Chemical precipitation at the freezing temperature of ~4°C has directly yielded layered rare-earth hydroxide [LRH, Ln2(OH)5NO3·nH2O, Ln = Y0.95Eu0.05] nanosheets (up to 7 nm thick) for the Y/Eu binary system, with the interlayer NO3− exchangeable with SO42−. Calcining the sulfate derivative at 1100°C for 4 h produces well-dispersed and readily sinterable Ln2O3 red phosphor powders (~14.8 m2/g) that can be densified into highly transparent ceramics via optimized vacuum sintering at the relatively low temperature of 1700°C for 4 h (average grain size ~14 μm; in-line transmittance ~80% at the 613 nm Eu3+ emission or ~99% of the theoretical transmittance of Y2O3 single crystal). Our systematic studies also found that (1) the extent of SO42− exchange and the interlayer distance of LRH are both affected by the SO42−/Ln3+ molar ratio (R), and an almost complete exchange is achievable at R = 0.25 as expected from the chemical formula (one SO42− replaces two NO3− for charge balance). The optimal R value for sintering, however, was found to be 0.03; (2) The Ln3+ concentration for LRH synthesis substantially affects properties of the resultant oxides, and hard agglomeration has been significantly reduced at the optimized Ln3+ concentration of 0.05–0.075 mol/L; (3) Sulfate exchange significantly alters the thermal decomposition pathway of LRH, and was found essential to produce well-dispersed and highly sinterable oxide powders; (4) Both the oxide powders and transparent ceramics exhibit the typical red emission of Eu3+ at ~613 nm (the 5D0→7F2 transition) under charge-transfer (CT) excitation. Red-shifted CT band center, stronger excitation/emission, and shorter fluorescence lifetime were, however, observed for the transparent ceramics.

Controlled Synthesis of Layered Rare-Earth Hydroxide Nanosheets Leading to Highly Transparent (Y0.95Eu0.05)2O3 Ceramics

The Yb:Lu2O3 precursor made up of spherical particles was synthesized through the co-precipitation method in the water/ethanol solvent. The 5 at% Yb:Lu2O3 powder is in the cubic phase after calcination at 1100 °C for 4 h. The powder also consists of spherical nanoparticles with the average particle and grain sizes of 96 and 49 nm, respectively. The average grain size of the pre-sintered ceramic sample is 526 nm and that of the sample by hot isostatic pressing grows to 612 nm. The 1.0 mm-thick sample has an in-line transmittance of 81.6% (theoretical value of 82.2%) at 1100 nm. The largest absorption cross-section at 976 nm is 0.96×10−20 cm2 with the emission cross-section at 1033 nm of 0.92×10−20 cm2 and the gain cross sections are calculated with the smallest population inversion parameter β of 0.059. The highest slope efficiency of 68.7% with the optical efficiency of 65.1% is obtained at 1033.3 nm in quasi-continuous wave (QCW) pumping. In the case of continuous wave (CW) pumping, the highest slope efficiency is 61.0% with the optical efficiency of 54.1%. The obtained laser performance indicates that Yb:Lu2O3 ceramics have excellent resistance to thermal load stresses, which shows great potential in high-power solid-state laser applications.

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Fabrication, microstructures, and optical properties of Yb:Lu2O3 laser ceramics from co-precipitated nano-powders

In this article, we report on the fabrication and optical properties of highly transparent yttria ceramics for lasers active media with broadband gain profile. Laser synthesis method was used to produce Y2O3-based nanopowders doped with 1 mol.% Nd3+ or Yb3+ for these transparent ceramics. The additives of sesquioxides Lu2O3 and Sc2O3 were used along with ZrO2 to disorder the crystalline structure. The porosity and average grain size decrease with these additives and the emission bandwidths of Nd3+ (4F3/2 → 4I11/2) and Yb3+ (2F5/2 → 2F7/2) transitions widen to 40 and 60 nm, respectively. Laser operation with the slope efficiency of 29% was obtained in [(Yb0.01Lu0.24Y0.75)2O3]0.88(ZrO2)0.12 ceramic sample.

Fabrication and optical properties of Y2O3-based ceramics with broad emission bandwidth

The results of theoretical and experimental study of thermal lensing in diode-pumped Yb:YVO4 laser crystal,
Yb:Y2O3 and Yb:Sc2O3 laser ceramics are presented. Shown, that influence of thermo-lensing effect is necessary to
consider for creation of effective high-intensity femtosecond Yb-doped laser systems.

Measurement of thermal lensing in end-pumped Yb-doped yttrium vanadate crystal and sesquioxide laser ceramics

The development of combined enrichment technologies becomes more significant due to the decreasing of the processed ores quality and involvement in the processing of poor, refractory ores. The difficulty in the flotation enrichment of mixed and oxidized polymetallic ores and intermediate products lies in the effective sulfidization of the surface of oxidized minerals. The sodium sulfide reagent used in flotation does not always provide complete sulfidization of the mineral surface. On the intermediate product of lead-zinc ores related to the phase composition of mixed ores, flotation studies were carried out on the original product and after preliminary sulfidization by the pyro-metallurgical method. It was found that in the pre-sulfidizied product, the extraction of zinc increased to 17.23 %, and lead to 10.07 %, compared with the original product without pre-treatment.

K. V. Polyakov

Papers

Fabrication and optical properties of Y2O3-based ceramics with broad emission bandwidth

Measurement of thermal lensing in end-pumped Yb-doped yttrium vanadate crystal and sesquioxide laser ceramics

Flotation studies of the middling product of lead-zinc ores with preliminary sulfidizing roasting of oxidized lead and zinc compounds