Fabrication of high-efficiency Yb:Y2O3 laser ceramics without photodarkening

High-efficiency Yb:Y₂O₃ laser ceramics were fabricated using the vacuum-sintering plus hot isostatic pressing (HIP) without sintering additives. High-purity well-dispersed nanocrystalline Yb:Y₂O₃ powder was synthesized using a modified co-precipitation method in-house. The green bodies were first vacuum sintered at a temperature as low as 1430°C and then HIPed at 1450°C. Finally, the samples were air annealed at 800°C for 10 h. Although no sintering aids were used, full density of the samples with excellent optical homogeneity and an inline transmission of 80% at 400 nm could be obtained. Moreover, photodarkening phenomenon was not detected in the ceramics. Preliminary laser experiment with the fabricated ceramics in a two-mirror cavity has demonstrated 32 W continuous-wave (CW) output at ∼1077 nm with an optical-to-optical conversion efficiency of 58.2%. To the best of our knowledge, this is so far the highest CW output power and optical-to-optical conversion efficiency achieved with the Yb³⁺-doped sesquioxide ceramics in a simple two-mirror cavity.     

Effect of B2O3 addition on structure and properties of Yb3+/Al3+/B3+-co-doped silica glasses

The homogeneous Yb³⁺/Al³⁺/B³⁺-co-doped silica glasses were prepared via a sol-gel method. The impact of B₂O₃ addition on the physical and optical properties and network structure was systematically studied. The network structure was investigated by the Fourier Transform Infrared (FT-IR), Raman spectra, and Solid State Nuclear Magnetic Resonance (SSNMR). Herein, B₂O₃ addition can continuously decrease the refractive index and density. When B₂O₃ is lower than 2 mol%, B₂O₃ addition can obviously decrease the scalar crystal field parameters, Yb³⁺ asymmetry degree, Yb³⁺ cross-sections, due to the generation of Yb–O–B bonds at the cost of partial Yb–O–Al/Si ones. When B₂O₃ is more than 2 mol%, FT-IR, Raman spectra, and SSNMR results indicate that further increased B atoms prefer to connect with Si and Al rather than Yb. Consequently, the above parameters are basically unchanged. Based on the results, an intuitive model of structure and properties evolution during the substitution of SiO₂ by B₂O₃ has been established.     

Effect of Yb concentration on the microstructures,spectra, and laser performance of Yb: CaF2 transparent ceramics

Ytterbium-doped calcium fluoride transparent ceramics is considered as a promising laser gain medium. How to prepare low scattering loss ceramics is the main challenge at present. In this study, a simple route of hot-pressing method was introduced to fabricate high optical quality of Yb: CaF₂ laser ceramics with different concentration of Yb ions. The influence of Yb concentration on the particle sizes of the powders, microstructure, fluorescence spectra, output power, and laser emitting spectra of Yb: CaF₂ transparent ceramics was discussed. About 976 nm LD pumped CW laser operation has been demonstrated in 1, 2, 4, and 5 at.% Yb doped CaF₂ ceramics. A maximum average output power of 0.809 W was obtained for the 5 at.% Yb: CaF₂ ceramics with the slope efficiency was 26%.     

Synthesis of non-agglomerating submicron/nano-Yb2Si2O7 powders by a carbon-coated coprecipitation method

We herein report a novel carbon-coated coprecipitation method to synthesize non-agglomerating submicron/nano-β-Yb₂Si₂O₇ powders. Yb(C₂H₃O₂)₃·4H₂O and silica sol (alkaline) were chosen as the ytterbium source and silicon source, respectively. A carbon surface layer is processed using sucrose as carbon source to hinder the contact and sintering of β-Yb₂Si₂O₇ particles during heat treatment under a protective atmosphere, and then the carbon layer could be completely removed by inletting air at 900°C during cooling process. The as-synthesized Yb₂Si₂O₇ powders demonstrate an average size of 271 nm with a narrow distribution of 142–531 nm. The results show that the carbon layer could successfully solve the severe agglomeration or sintering of nanometer β-Yb₂Si₂O₇ particles during the calcination process. The as-developed carbon-coated coprecipitation technique is an effective method to fabricate high purity submicron/nano-Yb₂Si₂O₇ powders.     

Yb∶LuScO_3晶体的超精密光学加工及其激光性能

Yb∶LuScO_3晶体作为固体激光器的新型增益介质,其面形和表面质量严重影响激光器的光束质量,因此探索Yb∶LuScO_3晶体的超精度光学加工工艺参数具有重要意义。本文系统开展了Yb∶LuScO_3晶体超精密光学加工的工艺参数研究,针对Yb∶LuScO_3晶体在加工过程中容易破裂和表面质量较差的问题,提出了拼接上盘和树脂铜盘抛光垫的关键技术。首先,使用COMSOL Multiphysics有限元软件对拼接工艺中选取的不同保护垫料的应力进行仿真。接着,研磨阶段逐步减小B_4C磨料的粒径。然后,粗糙阶段使用树脂铜盘作为抛光垫,并对树脂铜盘抛光垫的作用进行了分析。最后,使用激光二极管泵浦加工好的样品进行激光输出实验。实验结果表明:基于该技术加工后的晶体表面粗糙度RMS=0.296 nm,面形精度PV=53 nm。在1 086 nm处获得了8.3 W的连续激光输出,斜效率为58%。该加工方法可以广泛应用于Yb∶LuScO_3晶体的高精度加工。     

Structural,morphological and up-converting luminescence characteristics of nanocrystalline Y2O3:Yb/Er powders obtained via spray pyrolysis

Sub-micronic, spherical Y₂O₃:Yb/Er particles comprising clustered nano-units (70 nm) were prepared via ultrasonic spray pyrolysis from pure nitrate precursor solutions with different Yb/Er dopant ratios. The particles were additionally thermally treated at 1100 °C for 12, 24 and 48 h. The structural and morphological characteristics of particles were studied by X-ray powder diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy dispersive X-ray analysis and specific surface area (BET) and were further correlated with their advanced optical properties. For the recorded up-conversion emissions, originating from the following Er³⁺ transitions: [²H_9/2→⁴I_15/2] in blue (407–420 nm); [²H_11/2, ⁴S_3/2→⁴I_15/2] green: 510–590 nm; and [⁴F_9/2→⁴I_15/2] in red (640–720 nm) spectral region, the corresponding lifetimes were acquired in the wide temperature range (10–300 K). The most intense green up-conversion emission with the long decay of 550 ms is recorded for Y_1.97Yb_0.02Er_0.01O₃ particles thermally treated at 1100 °C for 24 h.     

Two micrometer fluorescence emission and energy transfer in Yb3+/Ho3+ co-doped lead silicate glass

Enhanced 2.0 μm and visible up-conversion emissions from Ho³⁺ via Yb³⁺ sensitization in lead silicate glasses have been obtained under the excitation of 980-nm laser diode. The possible energy transfer mechanism has been analyzed based on the photoemission spectroscopy and lifetime measurement. The lifetime of Ho³⁺: ⁵I₇ laser upper level has also been measured. Based on the absorption spectra, Judd–Ofelt parameters, spontaneous emission probability, the absorption, emission cross sections, and gain coefficients have been calculated and analyzed. The results indicate that the Yb³⁺/Ho³⁺ co-doped lead silicate glass has potential application in mid-infrared wavelengths.     

Investigation of the effect of ytterbium doping on photoluminescence and photocatalytic activity of Li4Ti5O12

This work reports the combined effect of the morphology and crystallization to investigate the role of Yb³⁺ as an additive in Li₄Ti₅O₁₂ crystals on its photocatalytic and photoluminescence (PL) properties. With the pure phase, the synthesized samples have a spherical morphology and spherical structure with good crystallinity and uniform particle size distribution. Li₄Ti₅O₁₂ doped with ytterbium (Yb³⁺), were obtained by a new optimized hydrothermal approach. The crystal properties and surface morphology of the synthesized compounds were examined by X-ray diffraction method and field emission scanning electron microscopy. Bond structures and surface areas were investigated by Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller analyses. Finally, the excitation and emission spectra were obtained by a PL spectrophotometer. The PL results show that room-temperature PL of Yb³⁺ doped Li₄Ti₅O₁₂ phosphor has an emission peak at 710 nm which can be attributed to Li₄Ti₅O12 crystal defect emission. Moreover, it has been found that Yb doping resulted in enhancement of photocatalytic activity, evaluated by monitoring the degradation of methylene blue solution. Note that, 0.01% Yb doped lithium titania phosphor exhibited excellent photocatalytic activity.     

Tunable multicolor upconversion luminescence of Yb3+ sensitized Na3La(VO4)2 crystals

Multicolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb³⁺-sensitized Na₃La(VO₄)₂ upconversion luminescence crystals are synthesized by the solid-state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na₃La(VO₄)₂:Yb³⁺,Tm³⁺, Na₃La(VO₄)₂:Yb³⁺,Er³⁺, and Na₃La(VO₄)₂:Yb³⁺,Ho³⁺ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb³⁺-sensitized system are discussed in detail. In the Na₃La(VO₄)₂ host material, the Yb³⁺/Ho³⁺ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho³⁺ ion ⁵I₆ level, which provides the possibility of three primary color luminescence under 980 nm excitation.     

Probing structure of ytterbium stabilized Pr-doped zirconia obtained by microwave hydrothermal method

Nanoparticles of ZrO₂:Pr stabilized with ytterbium in the range 0.5%mol.-20%mol. were synthesized. Crystallite sizes depended on Yb concentration. Red luminescence resulting from ¹D₂→³H₄ transition of Pr³⁺ is present in all the samples. Additionally in the samples calcined at 1200 °C blue-green luminescence from ³P₀ level of Pr³⁺ was found. This emission was more intense than red one. Intensity of the ³P₀→³H₄ luminescence depended on ytterbium content and was found to be the highest at 20% mol. Yb. Luminescence study had shown, that ytterbium introduced additional lattice defects. Some quantity of praseodymium activator ions were found to be present at +4 state and changed its valence to +3 as ytterbium content had risen.