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Ho‐doped sesquioxide is one of the most important laser gain media for 2 micron wavelength band laser applications. It is hard to be transparent by sintering because of its high melting point. Herein, the structural and spectral properties of 0.5 at% Ho:(Y1−xScx)2O3 (x = 0, 0.3, 0.5, 0.7, 1.0) ceramics fabricated by vacuum pressureless sintering are studied. Then, 0.5 at% Ho:(Y0.7Sc0.3)2O3 transparent ceramics with 1.0 at% ZrO2 as a sintering aid are prepared by vacuum pressureless presintering (1680 °C for 4 h) combined with hot isostatic pressing sintering treatment (1600 °C/190 MPa for 3 h). The transmittance of Ho:(Y0.7Sc0.3)2O3 ceramic reaches 80.8% at 1100 nm (6 mm in thickness), which is close to its theoretic value. The addition of ZrO2 has no significant influence on spectroscopic properties of 0.5 at% Ho:(Y0.7Sc0.3)2O3 ceramics. [ABSTRACT FROM AUTHOR]

Dy 3+ -doped Y 2 O 3 ceramics were fabricated by Spark Plasma Sintering method. The effect of sintering temperature on the microstructure and the optical transmittance of the ceramics was studied. The maximum in-line transmittance of Dy:Y 2 O 3 ceramics with thickness of 1 mm was 74.5% at 574 nm when sintering temperature was 1550 ℃. The spectroscopic parameters were determined by Judd-Ofelt theory based on the room temperature absorption spectra. The peak emission cross section for the 4 F 9/2  →  6 H 13/2 transition was calculated to be 0.569 × 10 −20  cm 2 . The fluorescence decay curve and quantum efficiency of the 4 F 9/2 multiplet were measured to be 269.2 μs and 37.1%, respectively. [ABSTRACT FROM AUTHOR]

Transparent Sm:Y 2 O 3 ceramics were fabricated by spark plasma sintering (SPS). The effects of LiF additive and sintering temperature on the microstructure and optical transmittance of the Sm:Y 2 O 3 ceramics were investigated. The optimal content of LiF additive and sintering temperature was found to be 0.3 wt% and 1500 ℃. The transmittance of Sm:Y 2 O 3 ceramics with a thickness of 1.7 mm reached 75.3% at 609 nm, which is about 94% of the theoretical value. The average grain size of the sample was about 50 µm. [ABSTRACT FROM AUTHOR]

Tb3Al5O12 ( TAG) transparent ceramics were prepared by a reactive sintering method using presintering in a muffle furnace combined with hot isostatic pressing ( HIP) sintering. The dilatometric, differential scanning calorimetry-thermogravimetric ( DSC- TG) curves and optical quality were investigated. The microstructure evolution of the TAG ceramic samples was clarified. Two successive transformations were found to generate a TAG phase, as observed in the dilatometric and DSC- TG curves and XRD patterns of TAG ceramics sintered at different temperature. The changes in average grain size and densification suggest that a 1600°C presintering temperature is suitable for HIP. The optical transmittance of the obtained 0.4 wt% TEOS: TAG transparent ceramics, which were fabricated by a new two-step sintering of presintering at 1600°C in a muffle furnace followed by HIP at 1650°C, can reach above 80% in the visible (vis) and near-infrared ( NIR) regions. Its transmittance was very close to the theoretical limit. To the best of our knowledge, this is the first time that TAG transparent ceramics with ideal optical quality were obtained without vacuum sintering. [ABSTRACT FROM AUTHOR]

Transparent Y 2 O 3 ceramics were fabricated by the solid-state reaction and vacuum sintering method using La 2 O 3 , ZrO 2 and Al 2 O 3 as sintering aids. The microstructure of the Y 2 O 3 ceramics sintered from 1550 °C to 1800 °C for 8 h were analyzed by SEM. The sintering process of the Y 2 O 3 transparent ceramics was optimized. The results showed that when the samples were sintered at 1800 °C for 8 h under vacuum, the average grain sizes of the ceramics were about 3.5 µm. Furthermore, the transmittance of Y 2 O 3 ceramic sintered at 1800 °C for 8 h was 82.1% at the wavelength around the 1100 nm (1 mm thickness), which was close to its theoretical value. Moreover, the refractive index of the Y 2 O 3 transparent ceramic in the temperature range from 30 °C to 400 °C were measured by the spectroscopic ellipsometry method. [ABSTRACT FROM AUTHOR]

In this paper, we report the fabrication of high-quality 5 at. % Er3+ ions doped SrF2 transparent ceramics, the potential candidate materials for a mid-infrared laser-gain medium by hot-pressing at 700 °C for 40 h using a chemically-derived powder. The phase structure, densification, and microstructure evolution of the Er:SrF2 ceramics were systematically investigated. In addition, the grain growth kinetic mechanism of Er:SrF2 was clarified. The results showed lattice diffusion to be the grain growth mechanism in the Er:SrF2 transparent ceramic of which highest in-line transmittance reached 92% at 2000 nm, i.e., very close to the theoretical transmittance value of SrF2 single crystal. Furthermore, the emission spectra showed that the strongest emission band was located at 2735 nm. This means that it is possible to achieve a laser output of approximately 2.7 μm in the 5 at. % Er3+ ions doped SrF2 transparent ceramics. [ABSTRACT FROM AUTHOR]

Nd:LuAG transparent ceramics were fabricated by the solid-state reaction under vacuum sintering using SiO 2 and MgO as sintering aids, commercial Lu 2 O 3 , Al 2 O 3 and Nd 2 O 3 as raw materials. The Nd doping concentration was adopted from 0 at. % to 1.3 at. %. The phase transformation and microstructure evolution of 1.3 at. % Nd:LuAG ceramics under different sintering temperature was investigated in detail. Meanwhile, the effects of Nd 2 O 3 on the grain growth were surveyed. The results shown that when the samples were sintered at 1780 °C, the 1.3 at. % Nd:LuAG ceramic had clean gain boundary, and the transmittance of it reached 83.8% at 1064 nm. [ABSTRACT FROM AUTHOR]

In this work, the TAG transparent ceramics doped with 0.4 wt.% TEOS and different concentration of MgO were fabricated by a reactive sintering process under vacuum sintering combined with hot isostatic pressing (HIP) treatment. The effect of MgO on the microstructure evolution and optical properties of delivered ceramics were investigated. The results showed that the TAG ceramics doped with 0.4 wt.% TEOS and 0.1 wt.% MgO exhibited the optimum optical transmittance, which can reach about 81% in the visible and near-infrared (NIR) regions. The addition of MgO inhibited the grain growth and accelerated the densification of TAG ceramic at the sintering temperature reached about 1600 °C. [ABSTRACT FROM AUTHOR]

(Tb x Y 1−x ) 3 Al 5 O 12 (x = 0.2, 0.5, 0.8) transparent ceramics were synthesized by a solid-state reaction and HIP. All the samples were pre-sintered at 1650 °C for 4 h in a muffle and later HIPed at 1650 °C for 3 h. (Tb 0.2 Y 0.8 ) 3 Al 5 O 12 transparent ceramics exhibit best microstructure with an average grain size of approximately 5.22 μm and optical transmittance of over 65% in the region of 500–1600 nm. Additionally, average grain sizes of all the samples are less than 10 μm. XRD scanning patterns indicate that only the (Tb 0.8 Y 0.2 ) 3 Al 5 O 12 samples have little secondary phases. [ABSTRACT FROM AUTHOR]

2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0, 0.1, 0.5 and 1) transparent ceramics were fabricated via vacuum sintering. The microstructural properties of the prepared ceramics were determined using XRD and SEM. The absorption cross-section of 2 at.% Tm, 1 at.% Dy:Y 2 O 3 ceramic was 0.53 × 10−20 cm2 with the FWHM of 43.59 nm. The increased cross-section originates from a large overlapping range appearing in the absorption spectrum of the Dy3+:6H 15/2 → 6F 5/2 and Tm3+:3H 6 →6H 4 transitions. The J-O intensity parameters Ω 2 , Ω 4 and Ω 6 and the fluorescence characteristics of the pivotal luminescent level of the Dy3+ ions were investigated. Under 793 nm excitation, the emission cross section of the Tm,Dy:Y 2 O 3 ceramic at 3094 nm was 3.63 × 10−21 cm2 with the FWHM of 355 nm. The fluorescence lifetimes of Dy3+:6H 13/2 level of 2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0.1, 0.5 and 1) ceramics were fitted to be 357 μs, 282 μs and 149 μs, respectively. In order to explore the quenching mechanism of Tm3+:3F 4 level, the fluorescence lifetimes of Tm3+:3F 4 of the 2 at.% Tm, xat.% Dy:Y 2 O 3 ceramics (x = 0, 0.1, 0.5 and 1) were measured to be 4.878 ms, 462 μs, 104 μs and 61 μs, respectively. The possible energy transfer mechanisms between Tm3+ and Dy3+ ions are discussed. The results show that adding Tm3+ ions to Dy:Y 2 O 3 ceramics can effectively enhance the 2.9 μm MIR through energy transfer. [ABSTRACT FROM AUTHOR]

Laser grade 7 at.% Er:Y 2 O 3 transparent ceramics with submicron grain size were fabricated by using one-step vacuum sintering followed by hot isostatic pressing (HIPing) technique. Through studying the sintering trajectory of Er:Y 2 O 3 ceramics, the sintering temperature zone where sufficient relative density (>96%), no pore-boundary separation, and sub-micron grain size (<1 μm) ceramic samples could be identified. The samples pre-sintered in this zone were readily densified by HIPing. To maximum the densification and achieve high transparency, it is critical to suppress the final-stage grain growth. After HIPing at 1520 °C, the Er:Y 2 O 3 ceramics were fully densified without further grain growth, and exhibited in-line transmission of about 81.6% at 2000 nm. Continuous wave (CW) room temperature laser operation of the Er:Y 2 O 3 transparent ceramic at 2.7 μm was demonstrated. [ABSTRACT FROM AUTHOR]

Sm3+ doped yttria transparent ceramics (Sm x Y 1-x) 2 O 3 (x = 0.01, 0.015, 0.03) were fabricated by Spark Plasma Sintering method. Absorption spectra, as well as emission spectra and luminescence lifetime were carried out at room temperature. Judd-Ofelt (J-O) theory was used to calculate the Ω t (t = 2, 4, 6) intensity parameters. The spontaneous transition probabilities, radiative lifetime, branching ratio, and stimulated emission cross-sections have been calculated for 4G 5/2 excited level. The emission cross section for the 4G 5/2 → 6H 7/2 transition at about 607 nm was calculated to be 6.73 × 10−22 cm2. The results indicate that Sm:Y 2 O 3 ceramic may be a potential reddish orange-light laser material around 607 nm. [ABSTRACT FROM AUTHOR]

• After co-doping Tb3+ ions, the Ω4/Ω6 increased 1.57 from to 1.66. • The branching ratios of the 3H 4 →3F 4 transition also strengthened. • The decay curve of 3F 4 level doped with different Tb3+ ions concentration decreased. • Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. Tm3+ and Tb3+ co-doped Y 3 Al 5 O 12 (YAG) ceramics were fabricated by high temperature solid state reaction under oxygen sintering. The absorption spectra, fluorescence spectra and fluorescence decay curves of Tm,Tb:YAG ceramics were measured. The spectral parameters of Tm,Tb:YAG ceramic were calculated. The lifetimes of Tm3+:3F 4 level of Tm,Tb:YAG ceramics were calculated to be 11.28, 2.12, 1.24, 0.63 and 0.49 ms for the Tb3+ doping concentration of 0, 0.1, 0.2, 0.35 at 0.5 at%, respectively. The co-doping Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. These results indicate that the addition of Tb3+ ions in Tm,Tb:YAG ceramic could be a promising technique for laser operation around 1.5 µm. [ABSTRACT FROM AUTHOR]

Yb,Ho:Y 2 O 3 ceramics have been fabricated by Spark Plasma Sintering method (SPS). The microstructure and transmittance of the ceramics sintered from 1623 K to 1673 K were analyzed. The highest in-line transmittance of Yb,Ho:Y 2 O 3 ceramic sintered at 1673 K reached almost 83% at 750 nm with the thickness of 1 mm. The absorption spectra, fluorescence spectra and fluorescence decay curve were recorded at room temperature. The Judd-Ofelt parameters Ω 2 , Ω 4 and Ω 6 were calculated to be 8.33 × 10−20 cm2, 1.81 × 10−20 cm2, and 0.82 × 10−20 cm2, respectively. The intense emission cross section of Yb,Ho:Y 2 O 3 ceramic was 3.43 × 10−20 cm2 at 2057 nm with full width at half maximum (FWHM) of 208 nm. The results indicate that Yb,Ho:Y 2 O 3 transparent ceramic can be a promising laser gain medium for laser operation around 2 μm. Image 1 • The highest in-line transmittance of Yb,Ho:Y 2 O 3 ceramic sintered at 1673 K reached almost 83% at 750 nm with the thickness of 1 mm. • The spectral characteristics were intensively investigated through Judd-Ofelt theory. [ABSTRACT FROM AUTHOR]

Photograph of Yb,Ho:YAG crystals grown by the μ-PD method. (a) Yb = 0.05, (b) 0.1, (c) 0.15. • Y 3 Al 5 O 12 (YAG) single crystals doped with a fixed Ho3+ content of 0.5 at.% and various Yb3+ contents (Yb = 5, 10 and 15 at.%) have been successfully grown by the micro-pulling-down (μ-PD) method. Y 3 Al 5 O 12 (YAG) single crystals doped with a fixed Ho3+ content of 0.5 at.% and various Yb3+ contents (Yb = 5, 10 and 15 at.%) have been successfully grown by the micro-pulling-down (μ-PD) method. The absorption spectra, fluorescence spectra and fluorescence decay curves were recorded at room temperature. The intense emission of Yb,Ho:YAG crystal centered at 2 μm corresponds to the 5I 7 → 5I 8 transition. Three intense emissions centered at 524–569 nm, 623–691 nm and 744–746 nm, correspond to the 5F 4 + 5S 2 → 5I 8 , 5F 5 → 5I 8 and 5F 4 + 5S 2 → 5I 7 transitions, respectively. The possible energy transfer mechanisms were discussed intensively. [ABSTRACT FROM AUTHOR]

Mid-infrared ZnSe 0.9 S 0.1 transparent mixed crystal ceramics were successfully fabricated by hot pressing (HP) in combination with post hot isostatic pressing (HIP). The phase structure of the as-fabricated mixed ceramics was found to be composed of cubic sphalerite, and the existence of any secondary phase was not detected. It was noticed that after post HIP treatment, the grain size increased greatly, and many closed pores in the samples disappeared. The specimens HP sintered at 1000 °C under 60 MPa and post HIP treated at 1300 °C under 196 MPa in the Ar atmosphere for six hours had the best transmission of 62.3% at 14 μm. • Mid-infrared ZnSe 0.9 S 0.1 transparent ceramics were fabricated by hot pressing in combination with hot isostatic pressing. • The samples pre-sintered at 1000°C and hot isostatic pressing treated at 1300 °C under 196 MPa had the best transmission. • The optimum transmission of ZnSe 0.9 S 0.1 ceramic reach 62.3% at 14 μm. [ABSTRACT FROM AUTHOR]