Lu2O3 Ceramics Research Articles

Preparation, structure and spectral properties of Eu3+-doped Lu2O3 scintillation ceramics

Lu2O3 scintillation ceramics doped with different concentrations of Eu3+ were prepared by SPS in a vacuum environment. The microstructural properties of the prepared ceramics were analyzed using XRD, SEM and EDS in details. Excited by the 395 nm, the Eu3+-doped samples display a prominent emission peak at 612 nm, corresponding to the transition 5D0→7F2. The PL spectra across various concentrations identified 3 at.% as the optimal doping concentration. The temperature-dependent PL spectra reveal the activation energy of approximately 0.266 eV for the 3 % Eu3+-doped Lu2O3 ceramic. Under 395 nm excitation, the lifetimes of xEu:Lu2O3 (x = 0.01, 0.03, 0.05 and 0.07) ceramics were fitted to be 1.07 ms, 1.02 ms, 0.99 ms and 0.92 ms, respectively. The XEL spectra of Eu3+-doped samples are consistent with their PL spectra, aligning well with the sensitivity range of the detector. These results demonstrate that Eu3+:Lu2O3 scintillation ceramics are ideal materials for scintillation detectors.

The origin of microstructural inhomogeneity in vacuum‐sintered ZrO2‐doped Lu2O3 transparent ceramics

AbstractHighly transparent Lu2O3 ceramics were prepared by using co‐precipitation combined with vacuum sintering method with ZrO2 as sintering aid. The effect of ZrO2 on densification, transmittance, and microstructure evolution of the Lu2O3 ceramics was carefully studied. It was found that the addition of ZrO2 was very effective in improving densification of Lu2O3. The highest transmittance (at 600 nm) of the 3 at.% ZrO2 doped Lu2O3 ceramic (1.6‐mm thickness) sintered at 1800°C reached 80.1%. Microstructural inhomogeneity was found after vacuum sintering with larger grain sizes at the central. The microstructural inhomogeneity mainly occurred in the final stage of sintering. Doping ZrO2 mitigated microstructural inhomogeneity and decreased markedly the grain size of Lu2O3 ceramics. Raman measurements indicated that the disordered structure was formed due to oxygen vacancy, and the oxygen vacancy concentration at the central was higher than at the peripheral. The oxygen vacancy concentration gradient is the dominant factor governing nonuniform microstructure evolution during vacuum sintering. Furthermore, a uniform microstructure was obtained by the inhibition of oxygen vacancy formation by the Lu2O3/ZrO2 double powder bed.

High efficiency in-band pumped Tm- and Ho-doped 2-μm solid-state lasers

The expansion of laser sources operating at 2-3 μm is motivated in large by strong absorption in atmospheric gases, liquid water, and plastics, critical for applications in remote sensing, soft and hard tissue surgery, and materials processing. 2-μm novel solid-state lasers based on Tm3+-doped ceramics (Lu2O3 or Y2O3) or YAP crystals in-band pumped by a fiber laser at 1670 nm are presented in this report. CW, actively or passively Q-switch operations of the Tm3+-doped lasers are described. The Tm3+ laser characteristics are compared with parameters of an in-band fiber-laser-pumped Ho3+:YAG laser. The 2-μm output of the lasers are used to pump the Cr2+-doped ZnSe or CdSe crystals. The lasers based on the Tm3+:Lu2O3 ceramics and the Tm3+:YAP crystal are also used as pump sources for mid-IR optical parametric oscillators (OPOs) or second-harmonic generators (SHGs). The high-efficiency oscillations are obtained at 3.8-4.1 μm in the OPOs based on a fun-out PPMg:LN; the SHGs provided the repetitively-pulsed radiations at 970-983 nm.

Fabrication and characterizations of Tm:Lu2O3 transparent ceramics for 2 μm laser applications

2 at.% Tm:Lu2O3 ceramics were fabricated by vacuum sintering plus hot isostatic pressing (HIP) from nano-powders without sintering aids. The resultant powders consist of spherical particles with the diameter of about 100 nm. The HIP post-treated ceramic sample has fine grains and clean grain boundaries, whose in-line transmittance reaches 82.1% at 2000 nm (1.3 mm thickness). The mechanical, thermal, and spectral properties were also investigated systematically. The thermal conductivity of the Tm:Lu2O3 transparent ceramics is 10.2 W·m−1·K−1 at room temperature. The absorption and emission cross-sections are 0.35 × 10−20 cm2 at 796 nm and 1.13 × 10−20 cm2 at 1943 nm, respectively. The laser performance was tested in quasi-continuous wave (QCW) conditions. A maximum laser output power of 0.45 W was obtained with a slope efficiency of 16.0%. Results indicate that Tm:Lu2O3 transparent ceramics is a promising gain medium for 2 μm laser applications.

Spectral characteristics of “mixed” sesquioxide Yb:(Gd,Lu)2O3 transparent ceramics

In this work, Yb3+-doped Gd1.4Lu0.5Yb0.1O3 optical quality ceramics were successfully fabricated for the first time, to the best of our knowledge. The absorption and emission spectra were measured, spectroscopic investigations of 1-μm emission were carried out, and optical gain properties were analysed. The stimulated-emission cross-sections were 9.7·10−21 cm2 and 3.7·10−21 cm2 (calculated using the Fuchtbauer-Ladenburg equation) at 1031 nm and 1073 nm respectively. The calculated values were close to the estimated value of emission cross-sections for other Yb-doped sesquioxides. All the results show that Yb:(Gd,Lu)2O3 ceramics can be used as a potential active medium for mid-infrared high-power lasers.

Efficiency degradation of laser ceramics caused by inappropriate dispersants and sintering aids

Lasing quality 8 at.% Yb:Lu2O3 laser ceramics were fabricated using nanocrystalline Yb:Lu2O3 powders synthesized with a modified coprecipitation method and either (NH4)2SO4 or PAA (Poly acrylic acid) as a dispersant. Although using (NH4)2SO4 as a dispersant the calcinated Yb:Lu2O3 powders could have better sinterability, and the sintered Yb:Lu2O3 ceramics could even have higher in-line transmittance, it was found that the laser ceramics always had much lower lasing efficiency than those fabricated with PAA as a dispersant. We show that the efficiency degradation of the laser ceramics is due to the photodarkening caused by using (NH4)2SO4 as a dispersant.

Study of densification mechanisms during Spark Plasma Sintering of co-precipitated Ho:Lu2O3 nanopowders: Application to transparent ceramics for lasers

This work was focused on the determination of densification mechanisms during Spark Plasma Sintering (SPS) of Ho:Lu2O3 nanopowders. Strong variation of the stress exponent n was evidenced during the sintering process. At low relative density (i.e. ρ < 66 %), n = 3 and powder particles rearrangement and coalescence take place because of high value of effective stress and low size of primary nanoparticles. Then, for ρ between 66 % and 85 %, the stress exponent decreases to n = 2 then n = 1. Such values were related to Rachinger then Lifshitz sliding mechanisms, the last one was associated with an average activation energy of 565 kJ.mol−1. At the final densification stage (ρ > 85 %), the stress exponent suddenly increases to 4 in accordance with a power-law creep. From these investigations, an optimized thermomechanical cycle was proposed to obtain highly transparent Ho:Lu2O3 ceramics suitable for laser applications.

1940 nm, 1966 nm and 2066 nm multi-wavelength CW and passively-Q-switched operation of L-shaped Tm3+:Lu2O3 ceramic laser in-band fiber-laser pumped at 1670 nm

A Tm3+:Lu2O3 ceramics laser with the L-shaped cavity in-band pumped by a fiber laser at 1670 nm was studied in CW and passively Q-switched multi-wavelength regimes. The CW laser operated at 2066 nm at the weak pump power and self-tuned to 1966 nm and further to 1940 nm at higher pump power. The maximum power in the CW regime at 1940 nm reached 9.5 W, while the average power of 3.6 W was registered in the Q-switched regime with the pulse repetition rate of 110–170 kHz and the pulse duration of 200–240 ns. The Q-switched operation was obtained using a Cr2+:ZnSe saturable absorber. Pulsed regime started at the shortest wavelength of 1940 nm and self-tuned to the double-wavelength of 1940 nm and 1966 nm at higher pump power.

Characterisation of passively Q-switched Yb:Lu2O3 ceramic laser based on graphdiyne absorber

A stable pulsed Yb:Lu2O3 ceramic laser using graphdiyne (GDY) as a saturable absorber has been successfully demonstrated for the first time. The nonlinear optical absorption of GDY was obtained by a homemade picosecond pulsed solid-state laser at ~1064 nm as the source, which indicate the feasibility of GDY in laser modulation. The passively Q-switched Yb:Lu2O3/GDY laser was carried out. A 288 mW maximum average output power was achieved. The obtained repetition rate, pulse energy and peak power were 46.20 kHz, 6.23 μJ and 3.85 W, respectively, when the absorbed pump power of Yb:Lu2O3 ceramics was 2.3 W. These results indicate that GDY is a promising saturable absorption material and is expected to be widely used in ceramic laser.

Optical spectra and gain properties of Er3+:Lu2O3 ceramics for eye-safe 1.5-μm lasers

The Er 3+ -doped Lu 2 O 3 ceramics were successfully prepared by high temperature vacuum sintering of nanopowders using lantana as a sintering additive. The absorption coefficient and absorption cross-section of Er 3+ ions in Lu 2 O 3 ceramics at 980 nm were 3.3 cm −1 and 1.65·10 −21 cm 2 , respectively. The emission cross-section at 1534 nm was calculated to be 9.1·10 −21 cm 2 . The fluorescence decay lifetime of 4 I 13/2 energy level was 7.2 ± 0.2 ms. The positive gain cross-section at 1534 nm can be achieved if the inversion ratio P is 0.5 or higher. All results show that Er:Lu 2 O 3 ceramics can be used as potential active medium for mid-infrared lasers operated at 1.5 μm. • The Er 3+ -doped Lu 2 O 3 ceramics were successfully prepared by vacuum sintering. • The absorption cross section of Er 3+ ions in Lu 2 O 3 ceramics were reported. • All results show that Er:Lu 2 O 3 ceramics can be used for 1.5 μm lasers.

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

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.

Hot isostatic pressing of transparent Yb3+-doped Lu2O3 ceramics for laser applications

Yb3+-doped Lu2O3 nanoparticles produced by laser ablation were used to fabricate transparent ceramics by a combination of pressureless sintering in vacuum (PS) followed by a hot isostatic pressing (HIPing). The samples were subjected to various PS and HIPing conditions and the microstructure evolution and its correlation with the transmittance were investigated. Relative densities of over 97% were achieved after PS at the temperatures of 1250–1700 °C. Rapid grain growth occurred within PS and HIPing temperatures above 1500 °C leading to formation of intragranular porosity which is deleterious for optical quality. Higher transmittance (81.7% at λ = 1080 nm) and ultrafine microstructure with an average grain size of 0.35 μm were obtained by PS at 1250 °C followed by HIPing at 1400 °C for 5 h under 207 MPa. Output power of 2.02 W with a slope efficiency of 46.5% was obtained under a quasi-continuous wave end pumping at 929.4 nm.

Fabrication of Yb:Lu2O3 Transparent Ceramics by Hot Isostatic Pressing: the Effect of Yb Doping Concentrations

Highly transparent ytterbium doped lutctium oxide (Yb:Lu2O3) transparent ceramics with different Yb doping concentrations (0.5–10 at% Yb) were fabricated from commercial powders by vacuum sintering combined with hot isostatic pressing (HIP) method. The effects of Yb3+ doping concentrations on the microstructure, optical performance and the thermal conductivity of Yb:Lu2O3 transparent ceramics were investigated. The grain size of Yb:Lu2O3 ceramics first decreased with Yb doping concentration increasing and then kept nearly unchanged at high Yb doping concentrations. Under 1750°C HIP sintering for 2h, The in-line transmittance of the 5 at.% Yb:Lu2O3 ceramics (3 mm thick) exceeds 81.52% at 1100 nm. And it had the average grain size about 2μm. As the doping concentrations increase, the overall thermal conductivity decreases slightly. The fluorescence emission spectrum implied high possibility of realizing laser output at 1080 nm by pumping at 980 nm.

Mid-IR Optical Parametric Oscillator Based on Periodically Polled LiNbO3 Pumped by Tm3+:Lu2O3 Ceramic Laser

Optical parametric oscillator based on a periodically poled MgO:LiNbO3 crystal pumped by a repetitevely pulsed Tm3+:Lu2O3 ceramics laser at 1966 nm was studied. The OPO average output power up to 530 mW at wavelength of 3.7–4.2 μm was achieved at the ceramics laser power of 7.9 W. The optical-to-optical efficiency of OPO energy conversion was up to 6.7%, and the slope efficiency was up to 8%.

A passively Q-switched compact Er:Lu2O3 ceramics laser at 2.8 μm with a graphene saturable absorber

We have demonstrated a passively Q-switched Er:Lu2O3 ceramics laser using a monolayer graphene saturable absorber (SA). Stable pulsed operation with watt-level average power was achieved by a compact linear cavity without focusing on the SA. This is the first demonstration of a passively Q-switched mid-IR Er:Lu2O3 laser using a graphene SA. A maximum pulse energy of 9.4 μJ and a peak power of 33 W were achieved with a 247 ns pulse duration. To our knowledge, this is the shortest pulse duration, highest pulse energy, and highest peak power obtained with a graphene SA in the 3 μm wavelength region.

Eu:Lu2O3 transparent ceramics fabricated by vacuum sintering of co-precipitated nanopowders

Europium doped lutetium oxide (Eu:Lu2O3) nanopowders were synthesized by a co-precipitation method using hydrogen carbonate (AHC) as a precipitant. Influence of the terminal pH value on properties of the Eu:Lu2O3 precursors and calcined powders was investigated. It is found that the terminal pH value has little influence on compositions of the precursors, and all the powders calcined at 1100 °C show good crystallinity. However, the terminal pH value has significant influence on morphology and agglomeration degree of both the precursors and the calcined powders. The powders are found to have the optimal dispersity with the average particle size of 68 nm when the terminal pH is 6.57. Using the nanopowders as starting materials, Eu:Lu2O3 transparent ceramics were fabricated by vacuum sintering at 1700 °C for 30 h. The ceramics prepared from the powders whose terminal pH is 6.57 were found to have the best transparency and the in-line transmittance reaches 68% at 611 nm. The influence of vacuum sintering temperatures on the microstructure and transmittance of the Eu:Lu2O3 transparent ceramics was also investigated. The Eu:Lu2O3 ceramics sintered at 1825 °C for 30 h show the highest in-line transmittance of 72% at 611 nm. The average grain size of the prepared Eu:Lu2O3 ceramics is about 454 μm and the light output of the sample is about 10 times higher than that of commercial BGO single crystal.

Submicron‐grained Yb:Lu2O3 transparent ceramics with lasing quality

AbstractWe report on our recent progress of fabricating Yb3+‐doped Lu2O3 transparent ceramics for 1 μm solid‐state laser application. Well‐dispersed 3.3 at.% Yb:Lu2O3 nanopowders were synthesized using a co‐precipitation method. Without using any sintering aids, the Yb:Lu2O3 nanopowders could be densified by vacuum sintering at 1500°C/10 hours followed by HIPing at 1480°C/4 hours. Such obtained Yb:Lu2O3 ceramics had not only dense microstructure and submicron grain size of about 0.6 μm, but also in‐line transmission of 80.0% at 600 nm. Preliminary continuous wave (CW) laser experiments with an uncoated Yb:Lu2O3 ceramic slab have demonstrated highly efficient CW laser oscillation at 1079.8 nm.

Fabrication and properties of Eu:Lu2O3 transparent ceramics for X-ray radiation detectors

Europium-doped lutetium oxide (Eu:Lu2O3) nano-powders were synthesized by a co-precipitation method from europium and lutetium nitrates using ammonium hydrogen carbonate (AHC) as the precipitant. Fine and low-agglomerated powders with average particle size of 68 nm were obtained by calcining the precursor at 1100 °C for 4 h. Using this powder as starting material, Eu:Lu2O3 transparent ceramics with the average grain size of ∼46 μm were fabricated by vacuum sintering at 1650 °C for 30 h, whose in-line transmittance reaches 66.3% at 611 nm. The influences of air annealing on optical transmittance, decay time, spectroscopic properties, light output and thermally stimulated luminescence of Eu:Lu2O3 ceramics were investigated in detail. Based on radioluminescence spectra, the light output of the annealed Eu:Lu2O3 ceramics is 10 times higher than that of the commercially available BGO single crystal, and it indicates that transparent Eu:Lu2O3 scintillation ceramics is a promising candidate for X-ray radiation detectors.

Fabrication, microstructure and spectroscopic properties of Yb:Lu2O3 transparent ceramics from co-precipitated nanopowders

Ytterbium doped lutetium oxide (Yb:Lu2O3) transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) of the powders synthesized by the co-precipitation method. The effects of calcination temperature on the composition and morphology of the powders were investigated. Fine and well dispersed 5 at% Yb:Lu2O3 powders with the mean particle size of 67 nm were obtained when calcined at 1100 °C for 4 h. Using the synthesized powders as starting material, we fabricated 5 at% Yb:Lu2O3 ceramics by pre-sintering at different temperatures combined with HIP post-treatment. The influence of pre-sintering temperature on the densities, microstructures and optical quality of the 5 at% Yb:Lu2O3 ceramics was studied. The ceramic sample pre-sintered at 1500 °C for 2 h with HIP post-treating at 1700 °C for 8 h has the highest in-line transmittance of 78.2% at 1100 nm and the average grain size of 2.6 µm. In addition, the absorption and emission cross sections of the 5 at% Yb:Lu2O3 ceramics were also calculated.

Effect of rate-controlled sintering on characteristics of hot isostatically pressed transparent Yb-doped Lu2O3 ceramics

Ytterbium-doped transparent lutetium oxide (Yb:Lu2O3) ceramics were fabricated from laser ablated nanoparticles via vacuum pre-sintering followed by hot isostatic pressing (HIPing). Nano-sized powder was uniaxially pressed and pre-sintered at 1550 °C using a conventional regime composed of a slow ramp (3 °C/min) with subsequent holding (CRH), and a rate-controlled sintering (RCS) regime consisting of a progressive reduction in densification rates. Although the pre-sintered samples approached identical relative density of ∼97%, the average grain size was decreased more than 30% by application of RCS regime. Pre-sintered Yb:Lu2O3 compacts were then HIPed to achieve full density and transparency. The optical attenuation coefficient of the ceramic pre-sintered by CRH regime was found to exceed that of the ceramic fabricated using RCS method by a factor of 2.1 at the wavelength of 1080 nm.