Intense broadband 3.1 μm emission in Er3+-doped fluoroaluminate-tellurite glass for mid-infrared laser application

Er³⁺ single doped fluoroaluminate-tellurite glasses were made by employing a conventional melt-quenching technique. A strong fluorescence around 3.1 μm was achieved from Er³⁺-doped fluoride glasses, under a 980 nm laser diode pump, which was assigned to the Er³⁺: ⁴S_3/2 → ⁴F_9/2 radiation transition process. The up-conversion and mid-infrared spectra of emission for fluoroaluminate-tellurite glasses with various concentrations of Er³⁺ ions dopant was researched. In addition, the calculated fluorescence lifetime value about 3.1 μm reaches 0.48 ms. The findings indicate that fluoroaluminate-tellurite glasses doped with Er³⁺ have prospects of being developed into 3.1 μm mid-infrared fiber and laser materials.     

Intense emission at 2.9 μm from Yb3+/Ho3+ co-doped TeO2–Ga2O3–ZnO tellurite glasses

Mid-infrared lasers have important applications in infrared countermeasures, sensing, environmental monitoring, biomedicine, and many military and civilian fields. In this work, an intense emission at 2.9 μm from Yb³⁺/Ho³⁺ co-doped TeO₂-Ga₂O₃-ZnO (TGZ) glass was reported. The 2 μm, 1.2 μm and visible emissions were also performed to understand the competitive luminescent mechanism. With the increase in Yb³⁺ concentration, all the emissions of Ho³⁺ increased, whereas the emission of Yb³⁺ decreased due to the phonon-assisted energy transfer from Yb³⁺ to Ho³⁺. The lifetimes of optimized 3 mol% Yb₂O₃ and 1 mol% Ho₂O₃ co-doped TGZ glass, which has the maximum emission intensity, are 548 μs and 1.7 ms at 2.9 and 2 μm, respectively. The Judd–Ofelt intensity parameters, absorption, and emission cross sections were calculated to evaluate the mid-infrared fluorescence properties of this new glass matrix material. The gain coefficients show that the 2 and 2.9 μm laser gain can be realized by small pump energy, indicating that this glass is a promising medium for the mid-infrared optical fiber laser.     

Two-wavelength excitation–driven robust operation of green up-conversion emission in Er3+-doped oxyfluoride glass–ceramic

Efficient optical modulation enables a significant improvement of optical conversion efficiency and regulation of optical response rate, showing great potential for optoelectronics applications. However, the weak interaction between photons poses a strong obstacle for manipulating photon–photon interactivity. Here, upon simultaneous excitation of 850 and 1550 nm, a fast–slow optical modulation of green up-conversion (UC) luminescence in oxyfluoride glass ceramics containing NaYF₄:Er³⁺ nanocrystals can be achieved. Compared with the sum of luminescence intensity excited by the two single-wavelengths, green UC luminescence excited by simultaneous two-wavelength presents an obvious increase by approximate six times. Interestingly, the response rate of green UC luminescence relies on the pump strategy of two-wavelength excitation, showing as high as two times of the fast–slow response difference. The fast–slow optical modulation of green UC luminescence under two-wavelength excitation is promising for emerging applications in all-optical switching.     

Fabrication and spectroscopic investigations on Er3+, Ho3+: SrF2 transparent ceramics for 2.7 μm emission

3 at.% Er³⁺, x at.% Ho³⁺: SrF₂ (x = 0, 0.05, 0.1, 0.5, 1, 2) transparent ceramics, as the potential material for the 2.7 μm solid-state laser, were fabricated by hot-pressed sintering. XRD, TEM, SEM, and EDS measurements were used to investigate the phase composition, morphology, microstructure, and distribution of the elements of the nanoparticles and transparent ceramics. Results showed that the Er³⁺ ions and Ho³⁺ ions do not alter the SrF₂ crystal structure, and they are distributed uniformly in the sample. With the increase of the Ho³⁺ doping concentration, the lattice parameter decreased from 5.799 Å to 5.784 Å, and the average grain size decreased gradually. The maximum transmittance of as-obtained ceramics is approximately 93 % which is close to the theoretical transmittance of SrF₂. Moreover, the absorption spectra, emission spectra, and the lifetime of Er³⁺ and Ho³⁺ were investigated. The energy transfer processes between Er³⁺ and Ho³⁺ were discussed. After co-doping Ho³⁺, the lifetime difference between Er³⁺:⁴I_11/2 and Er³⁺:⁴I_13/2 levels was shortened from 8.50 ms to 1.12 ms. All the results show that the incorporation of Ho³⁺ with proper doping concentration is beneficial for achieving 2.7 μm laser output in Er³⁺: SrF₂ transparent ceramics.     

Moderate temperature plastic deformation in amorphous Al2O3–ZrO2 ceramics containing different amount of nanocrystals

Abstract

The differences in the deformation behaviour and the microstructures among the amorphous Al₂O₃–ZrO₂ ceramics containing different amount of nanocrystals were investigated. Therein, the amorphous sample without nanocrystals displayed large plastic deformation due to its large free volume change. With the increase in nanocrystals, the yield strength and plasticity of Al₂O₃–ZrO₂ ceramics were promoted. However, excess nanocrystals would induce the decrease in the plasticity.     

Large third-order optical nonlinearity of ZnO–Bi2O3–B2O3 glass–ceramic containing Bi2ZnB2O7 nanocrystals

Homogeneous transparent optical glass–ceramics precipitated with unique nonlinear crystals are promising materials for photonic applications. We have utilized heat treatment method to prepare transparent ZnO–Bi₂O₃–B₂O₃ glass–ceramic containing Bi₂ZnB₂O₇ nonlinear nanocrystals. A large third-order nonlinear susceptibility χ⁽³⁾ of glass–ceramic is measured by Z-scan technique, which mainly attributed to unique [BiO₆] and [B₂O₅] units in Bi₂ZnB₂O₇ crystal structure and the quantum size effect of nanoparticles. The discovery is of great potential in the application of nonlinear optical integrated devices.     

Colloidal processing of Al2O3-doped zirconia ceramics with CaO–P2O5–SiO2 glass as additive

Well-dispersed concentrated aqueous suspensions of Al₂O₃-doped Y-TZP (AY-TZP), AY-TZP with 5.4 vol% of CaO–P₂O₅–SiO₂ (CaPSi) glass (AY-TZP5) and 10.5 vol% CaPSi glass (AY-TZP10), with ammonium polyacrylate (NH₄PA) dispersant were prepared to produce slip cast compacts. The rheological properties of 35 and 40 vol% slips were studied. The densification, microstructure as well as hardness and fracture toughness were investigated as a function of CaPSi glass content at 1300°C-1500°C. The optimum NH₄PA concentration of 35 vol% AY-TZP5 and AY-TZP10 slips at pH ~9 was found to be about 43% and 67% greater than that of AY-TZP slips; this behavior was related to the greater amounts of Ca²⁺ ions leached out from the CaPSi glass surface. The viscosity of stabilized 40 vol% slips with NH₄PA attained a minimum value at 5.4 vol% CaPSi glass addition, and resulted in a more dense packing of cast samples. AY-TZP5 can be sintered at a lower temperature (1300°C) compared to that of AY-TZP. AY-TZP5 exhibited a fine microstructure of tetragonal ZrO₂ (grain sizes below 0.3 µm), and ZrSiO₄–Ca₂P₂O₇ particles homogeneously distributed within the zirconia matrix. It presented similar fracture toughness and a slightly lower hardness compared to those of AY-TZP.     

Ce3+ induced broadband enhancement around 2 μm in Tm3+/Ho3+ co-doped tellurite glass

Tellurite glasses doped with Tm³⁺, Ho³⁺ and Ce³⁺ ions were prepared via melt-quenching to realise broadband and fluorescence enhancement in near-infrared (NIR) band. Under the pumping of a commercial 808 nm laser diode (LD), the emission bands at 2.0 μm, 1.85 μm, 1.47 μm, and 705 nm were observed in the Tm³⁺/Ho³⁺ co-doping glass samples, which originated from the transitions of Ho³⁺:⁵I₇→⁵I₈ and Tm³⁺:³F₄→³H₆, ³H₄→³F₄, ³F_2,3 → ³H₆, respectively. The existence of 2.0 μm band fluorescence is due to the energy transfer from the Tm³⁺:³F₄ level to the Ho³⁺:⁵I₇ level. This band overlaps with the 1.85 μm band which forms a broadband fluorescence spectrum in the range of 1600–2200 nm. In glass samples co-doped with Tm³⁺/Ho³⁺ with 0.085 mol% Ho₂O₃ and 1 mol% Tm₂O₃, the full width at half maximum (FWHM) of this broadband spectrum (1600–2200 nm) was as high as ∼370 nm. After introducing 0.6 mol% CeO₂, the emission intensity of broadband fluorescence increased by ∼50%, which was caused by the cross-relaxations between Ce³⁺ and Tm³⁺ ions. The lifetime of fluorescence decay was determined to prove the interactions among the doped rare-earth ions, the radiative parameters such as transition probability, branching ratio and radiative lifetime were calculated from the absorption spectra based on the Judd-Ofelt theory to better understand the observed luminescence phenomena. In addition, X-ray diffraction (XRD) confirmed the amorphous state structure of the synthesised glass samples, while Raman spectrum revealed the different vibrational structural units forming the glass network.     

Intense continuous-wave laser and mode-locked pulse operation from Yb3+-doped oxyfluoride glass–ceramic fibers

Ultrafast fiber lasers, due to their short pulse duration, excellent beam quality, and high brightness, are extensively used in precision processing, biomedicine, nonlinear optics, and spectroscopy. However, great challenges still exist in improving the optical conversion efficiency in glass-based gain media because of the high non-radiative transition probability. Here, we demonstrate an oxyfluoride glass–ceramic (GC) fiber containing NaYF₄:Yb³⁺ nanocrystal that enables enhanced 1064-nm continuous-wave laser output with an optical signal-to-noise ratio of 60 dB. Compared with the as-prepared glass fiber, the optical conversion efficiency of GC fiber is improved from 24.2% to 30.0%. The improvement of laser action is mainly caused by the preferential incorporation of Yb³⁺ into the NaYF₄ nanocrystal with low phonon energy. Using this well-developed GC fiber, we successfully built a passively mode-locked pulsed fiber laser that deliveries laser pulses with a pulse duration of 8.1 ps and a repetition frequency of 56.92 MHz. These results highlight that the GC strategy may provide a roadmap for the development of ultrafast fiber laser and the application of GC fibers in various optoelectronic fields.     

Emission properties of 1.8 and 2.3 μm in Tm<Superscript>3+</Superscript>-doped fluoride glass

In this work a Tm³⁺-doped fluoride glass with good thermal stability is prepared. Intensive 1.8 and 2.3 μm emissions are obtained when pumped by an 800 nm laser diode. And the 1.48 μm emission is limited because of the much strong radiation around 1.8 μm. On the basis of absorption spectrum, radiative properties are investigated and discussed according to Judd–Ofelt parameters (Ω₂, Ω₄, Ω₆) calculated by Judd–Ofelt theory. Besides, absorption and emission cross-sections of ³ F ₄ → ³ H ₆ transition are figured out and analyzed by using McCumber and Beer–Lambert theories. The high gain around 1.8 μm was predicted by the large σ_emiτ_rad product (29.8 × 10^–21 cm² ms). The results obtained indicate that the Tm³⁺-doped fluoride glass can be a promising 2.0 μm laser glass material.     

Multi-phase induced ultra-broad 1100-2100 nm emission of Ni2+ in nano-glass composites containing hybrid ZnGa2O4 and ZnF2 nanocrystals

A new type of Ni²⁺-doped dual-phase glass ceramics (GCs) is developed by a simple one-step thermal-induced crystallization process. The GCs thus obtained are embedded simultaneously with hybrid ZnGa₂O₄ and ZnF₂ nanocrystals (NCs). When pumped by a readily available 808 nm laser diode, an ultra-broad near-infrared (NIR) emission in a range of 1100−2100 nm is observed at room temperature. The NIR emission band with a full-width-at-half-maximum (FWHM) of more than 450 nm is comparable to the largest value ever reported in Ni²⁺-doped GCs, and much broader than those of single-phase GCs embedded with either pure ZnGa₂O₄ or ZnF₂ NCs. The microscopic morphologies of the embedded hybrid NCs, and especially the distribution of Ni²⁺ in the dual-phase GCs are studied by analytical transmission electron microscopy (TEM). The intriguing photoluminescence properties of Ni²⁺ are thoroughly investigated by steady-state and time-resolved emission spectra. The GCs demonstrated herein hold promise as broadband solid-state NIR-light sources.     

Realizing particle population inversion of 2.7 μm emission in heavy Er3+/Pr3+ co-doped low hydroxyl fluorotellurite glass for mid-infrared laser

In this work, the population bottleneck of Er³⁺: ⁴I_11/2 → ⁴I_13/2 was overcome for the first time in heavy Er³⁺/Pr³⁺ co-doped TeO₂–BaF₂–La₂O₃–LaF₃ (TBLL) low hydroxyl fluorotellurite glasses. Infrared emission spectra and fluorescence lifetime decay curves reveal that Pr³⁺ ions could deplete the electrons from the Er³⁺: ⁴I_13/2 level faster than those from the Er³⁺: ⁴I_11/2 under 980 nm excitation. Specifically, the energy transfer (ET) efficiency of the Er³⁺: ⁴I_13/2 → Pr³⁺: ³F_3,4 process (ET1) reached 96.27%, while that of the Er³⁺: ⁴I_11/2 → Pr³⁺: ¹G₄ process (ET2) is only 2.17% in the Er³⁺/Pr³⁺ co-doped glass. Additionally, the energy transfer mechanism of Er³⁺ and Pr³⁺ ions was investigated using the Dexter theory, where the energy transfer microscopic parameters C_D-A are 13.21 × 10⁻⁴⁰ cm⁶/s and 0.89 × 10⁻⁴⁰ cm⁶/s for the ET1 and ET2 processes, respectively. Finally, a numerical simulations laser model was developed to discuss the laser properties of the Er³⁺/Pr³⁺ co-doped TBLL fibers. The simulation results indicate that a 2.7 μm laser with a maximum output power of 2.26 W and slope efficiency of 13.89% could be achieved when the fiber background loss is reduced to 0.5 dB/m. The above results suggest that the Er³⁺/Pr³⁺ co-doped TBLL glass has great potential applications in mid-infrared fiber lasers.     

Glass-forming regions and enhanced 2.7 μm emission by Er3+ heavily doping in TeO2–Ga2O3–R2O (or MO) glasses

Er³⁺-doped fiber lasers operating at 2.7 μm have attracted increasing interest because of their various important applications; however, the intrinsic self-terminating effect of Er³⁺ and the reliability of glass hosts hindered the development of Er³⁺-doped fiber lasers. Herein, the glass-forming regions of a series TeO₂–Ga₂O₃–R₂O (or MO) (R = Li, Na, and Rb; M = Mg, Sr, Ba, Pb, and Zn) glasses are predicted by the thermodynamic calculation method. On this basis, the physical and optical properties of TeO₂–Ga₂O₃–ZnO (TGZ) glass are investigated in detail as an example. Under the excitation of 980 nm laser diode, the fluorescence intensity at 2.7 μm reaches a maximum in the heavily Er³⁺-doped TGZ glass. By contrast, the accompanying near-infrared fluorescence at 1.5 μm and upconversion green emissions at 528 nm and 546 nm are all effectively weaken. Furthermore, the lifetime gap between the ⁴I_11/2 upper laser level and ⁴I_13/2 lower laser level is sharply narrowed from 2.81 ms to 0.59 ms, which is beneficial to overcome the population conversion bottleneck. All results demonstrate that these newly developed ternary tellurite glass systems are promising candidates for near-/mid-infrared laser glass fiber, fiber amplifiers, and fiber lasers.     

Enhanced dielectric energy storage performance of A-site Ca2+-doped Na0.5Bi0.5TiO3–BaTiO3–BiFeO3 Pb-free ceramics

(1-x) (0.98Na_0.5Bi_0.5TiO₃–0.01BaTiO₃–0.01BiFeO₃)–xCaTiO₃ (NBB-xCT) ceramics were produced using traditional solid-state synthesis methods. The surface morphology, domain structure, and electrical properties of the ceramic samples were systematically studied. In addition, the temperature and frequency stabilities of the NBB-15CT sample at 200 kV/cm were tested. Generally, NBB-xCT ceramics exhibit a typical single perovskite phase structure. The results indicate that the NBB-15CT ceramics showed a high energy density of 3.14 J/cm³ at 250 kV/cm. The piezoresponse force microscopy (PFM) results showed that the addition of CT broke the macrodomains of the 0.98Na_0.5Bi_0.5TiO₃-0.01BaTiO₃-0.01BiFeO₃ ceramic and helped to form nanodomains, leading to an improved energy storage performance. The above performance indicates that the specimens possess very good temperature-and frequency-dependent energy storage performances at 30–150 °C and 1–100 Hz. Moreover, the electric energy storage and release in the NBB-15CT ceramic indicated that the power density could reach 55.30 MV/cm³ at 180 kV/cm. Therefore, the NBB-15CT ceramic is a promising material for electrical capacitors.     

Enhanced broadband NIR emission in glass–ceramic fibers containing Nd3+/Yb3+ co-doped YCa4O(BO3)3 disordered nanocrystal

Demands are increasing for ultrashort pulse laser in industrial applications, where the gain bandwidth of most optical fiber material is not wide enough, and developing a wide bandwidth gain medium is challenging. Glass–ceramic fibers containing Nd³⁺/Yb³⁺ co-doped YCa₄O(BO₃)₃ nanocrystals were fabricated by the molten core method and successive heat treatment. After a careful heat treatment, Nd³⁺/Yb³⁺ co-doped YCa₄O(BO₃)₃ nanocrystals were precipitated in the fiber core. Enhanced broadband near-infrared (NIR) emission from 850 to 1150 nm (bandwidth: ∼252 nm) was obtained in the glass–ceramic fiber compared to that of precursor fiber. These results suggest that the Nd³⁺/Yb³⁺ glass–ceramic fibers are promising for broadband NIR optical amplifications and lasers.     

Structure and optical properties of transparent Er3+-doped CaF2–silica glass ceramic prepared by controllable sol–gel method

Transparent Er³⁺-doped CaF₂–silica glass ceramics were prepared by the direct physical introduction of Er³⁺ doped CaF₂ nanocrystals into acid-catalyzed sol–gel silica glass. The physical methods of ball milling, ultrasonic baths, and stirring were investigated to disperse Er³⁺ doped CaF₂ nanocrystals in the silica sols. The CaF₂–silica sol mixture went through gelation and heat-treatment to form Er³⁺-doped CaF₂–silica glass ceramics. The morphology of Er³⁺ doped CaF₂ in silica glass did not change after heat-treatment at 600 °C for 10 h. The experimental results showed that Er³⁺ doped CaF₂ in the glass ceramic prepared with the assistance of ball milling possesses the best dispersity and homogeneity. The highest in-line transmittance of the glass ceramic reached up to 85% in visible region. Glass ceramic exhibits efficient up-conversion emissions corresponding to the Er³⁺:⁴F_9/2→⁴I_15/2 transition and long lifetime of ⁴F_9/2 level (1.73 ms) under 980 nm excitation.     

Transparent sol-gel glass ceramics containing β-NaYF4:Yb3+/Er3+ nanocrystals: Structure,upconversion luminescent properties and optical thermometry behavior

Transparent bulk glass ceramics (GCs) containing $\beta ?\mathit{NaY}{\mathrm{F}}_4:{\mathit{Yb}}^{3+}/{\mathit{Er}}^{3+}$ upconversion nanocrystals were successfully prepared via a new sol-gel route for the first time. The structure, composition and morphology of the as-fabricated glass ceramics are characterized by X-ray diffraction ($\mathit{XRD}$), scanning electron microscopy ($\mathit{SEM}$) and transmission electron microscopy ($\mathit{TEM}$), which confirm the segregation of β-NaYF₄ nanocrystals in silica glass matrix with the maintenance of their crystalline phase and microstructure. More significantly, intense upconversion (UC) emissions can be realized for ${\mathit{Yb}}^{3+}/{\mathit{Er}}^{3+}$ co-doped glass ceramics by profiting from low-phonon-energy environment of erbium ions in β-NaYF₄ nanophase. Furthermore, temperature-dependent UC emission performance of the present GC is systematacially investigated to explore their potential application in optical thermometry. Obviously, owing to intense UC emissions of $\beta ?\mathit{NaY}{\mathrm{F}}_4:{\mathit{Yb}}^{3+}/{\mathit{Er}}^{3+}$ nanocrystals and high transparency, superior chemical/mechanical stability of oxide glassy matrix, the as-fabricated GCs exhibit good temperature sensing performance and good thermostability for precise temperature detecting. It is expected that the preliminary research can give a reference for designing new transparent bulk GCs and may exploit a valid method for developing high-performance optical temperature sensors.     

Sintering properties and homogeneity of Ca2+-doped .65Y2O3–.35YCr0.5Mn0.5O3 NTC ceramics

Ceramics suitable for use over a wide temperature and having a negative temperature coefficient (NTC) based on .65Y₂O₃–.35YCr_0.5Mn_0.5O₃-doped with CaO were prepared by applying a solid-state reaction at different temperatures (1500–1650°C). The physical properties and scanning electron microscopy results revealed that dense NTC ceramics could be obtained by sintering at >1550°C. The effect of two different sintering methods on the properties of the NTC ceramics was studied, and the results indicated that the NTC ceramics obtained by employing the two-step sintering method exhibited better properties. The contents of Cr and Mn oxides in the NTC ceramic discs prepared by applying two-step sintering (1600°C) exhibited a decreasing trend from inside to outside. To quantify the diffusion rate, Fick's second law was used, and the diffusion coefficients of Cr and Mn oxides in the NTC ceramics were found to be 5.20 × 10^–5 and 2.36 × 10^–5 cm²/s, respectively. Resistivity and temperature analyses indicated that the resistivity (ρ₂₅), B_25/100, and B_700/1000 of the NTC ceramics were 1.61 × 10⁶ Ω cm, 2367 K, and 2697 K, respectively, which are suitable for a wide temperature range.     

Na2TiGeO5—A self-light-emitting phosphor with the stable structure and tunable emission resulted from Cr3+-doped for FEDs

For matching the high energy excitation by the low voltage electron beams, the phosphors with stable crystal structure and high energy level excitation band is necessary. In this work, it is interesting to find a suitable phosphor of Na₂TiGeO₅ with self-light emitting property. The tight crystal structure of Na₂TiGeO₅ formed by edge-shared NaO₆ and TO₅ polyhedrons corresponds to its good thermal stability and degradation resistance property. The results indicate that the PL and CL intensity can still remain beyond 80% and 90% at 150°C and after 1 hour electron beams bombardment, respectively. Under the 254 nm excitation, the bright blue light peaked at 460 nm can be detected and the light control has been realized with the Cr³⁺ doped, which changes blue light to cyan light. The high energy excitation is attributed to the charge transfer band (CTB) of Ti⁴⁺–O²⁻, which matches the electron beams. The bright CL emission light centered at 450 nm with good degradation resistance property has been detected. The results indicate its potential application in field emission display (FED)s.