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Enhanced tunable mechanoluminescence (ML) is obtained in orthorhombic phase compound LiYGeO4:Bi3+,Tb3+. An anti-counterfeiting device is designed, which demonstrates the potential application prospects in the dynamic anti-counterfeiting field.

Tunable luminescence from red to white in Pr3+ single-doped oxyfluoride glass and glass ceramic.

Mechanoluminescence peaked at 355 nm (Bi3+: 3P1→1S0) was observed in an orthorhombic phase compound of LiYGeO4:Bi3+, which has widened the mechanoluminescence spectral wavelength into UV range.

A deep-red to NIR ML phosphor of MgGeO3: Mn2+ is reported, and defect is believed to influence the ML properties by comparing the phosphor’s luminescent properties before and after Mn4+–Mn2+ self-reduction.

High-gain Tm

High-performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power. Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts have been of interest to researchers. Despite remarkable progress in moving TE fibers toward room-temperature TE conversion, the figure-of-merit value (ZT) and bending stability still need enhancement. Herein, interfacial-engineering-enhanced TE properties of micro-nano polycrystalline TE fibers fabricated by thermally drawing Bi

High-performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power. Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts are of interest to researchers. Despite remarkable progress moving TE fibers towards room-temperature TE conversion, the figure-of-merit value (ZT) and bending stability still need enhancement. Herein, we report interfacial engineering enhanced thermoelectric properties of micro-nano polycrystalline TE fibers fabricated by thermally drawing Bi2Te3-based bulks in a glass-fiber template. The interfacial engineering effect comes from generating stress-induced oriented nanocrystals to increase electrical conductivity and producing strain-distorted interfaces to decrease thermal conductivity. The resulting fibers achieve a 40% higher ZT (~1.4 at 300 K) than their bulk counterparts and show a reversible bending radius of 50 µm, approaching the theoretical elastic limit. This fabrication strategy works for a wide range of inorganic TE materials and benefits the development of fiber-based micro-TE devices.

We report a silicate-clad heavily Tm

N-type bismuth telluride (Bi2Te3) based thermoelectric (TE) fibers were fabricated by thermal drawing and Bridgman annealing, and the influence of Bridgman annealing on the TE properties of n-type Bi2Te3-based TE fibers was studied. The Bridgman annealing enhanced the electrical conductivity and Seebeck coefficient because of increasing crystalline orientation and decreasing detrimental elemental enrichment. The TE performance of n-type Bi2Te3-based TE fibers was improved significantly by enhancing the power factor. Hence the power factor increased from 0.14 to 0.93 mW/mK2, and the figure-of-merit value is from 0.11 to 0.43 at ~300 K, respectively.

Er3+ has been considered one of the most suitable sensitive ions of Ho3+ to generate 2 μm emission. In this work, luminescent properties and energy transfer mechanism of Er3+/Ho3+ co-doped lead silicate glass were systematically investigated under 980 and 1550 nm excitations, respectively. Based on the absorption spectra, the Judd-Ofelt intensity parameters, absorption and emission cross sections, and gain coefficient were calculated. The emission cross section of Ho3+: 5I7 → 5I8 transition is as large as 8 × 10−21 cm2. And the calculated maximum gain coefficient is 3.48 cm−1 at 2010 nm. In addition, the energy transfer efficiency between Er3+: 4I13/2 level and Ho3+: 5I7 level can reach 89.3% when the samples were pumped by a 980 nm laser diode. An intense 2 μm emission was obtained upon excitation of 1550 nm due to the large absorption cross section of Er3+ at 1550 nm and efficient energy transfer from Er3+: 4I13/2 level to Ho3+: 5I7 level. These results suggest that the Er3+/Ho3+ co-doped lead silicate glass has great potential for application as a mid-infrared laser material.

In this work, strong yellow emission was obtained in Dy3+ doped multi-component phosphate glass due to its high asymmetry and covalency of the local field and high phonon energy. The internal quantum efficiency was measured to be 39.27% and the figure of merit was calculated to be 210.53 pm2 × μs. What is more, silicate-clad Dy3+ doped multi-component phosphate core glass fiber was successfully drawn by using a rod-in-tube method, which has a strong fluorescence emission in yellow spectra band. The Dy3+ doping concentration is 2.6 wt.%, which is much larger than that of Dy3+ doped (0.2 wt.%) ZBLAN fiber. These results suggest that the silicate-clad Dy3+ doped multi-component phosphate glass fibers are potential host matrices for yellow laser.

Nd3+ doped multi-component phosphate glass was prepared by the conventional melt-quenching method. The absorption spectrum, emission spectrum, and fluorescence lifetime of the prepared glass were measured. Based on the absorption spectrum, Judd-Ofelt (J-O) intensity parameters, spectroscopic quality factor, absorption and emission cross-sections, and figure of merit were calculated and analyzed. What is more, multi-material fibers with Nd3+ doped multi-component phosphate glass core and silicate glass cladding were successfully drawn by using the molten core method. The Nd3+ doping concentration reaches as high as 3.82 × 1020 ions/cm3 (3.86 wt.%). More importantly, 1.05 μm amplified spontaneous emission (ASE) was realized in a 4-cm-long as-drawn multi-material fiber when pumped by an 808 nm laser diode (LD). These results suggest that the Nd3+ doped multi-component phosphate glass multi-material fibers are promising gain material for 1.05 μm fiber laser applications.

Tin selenide (SnSe) exhibits high thermoelectric (TE) performance, which is a promising TE candidate for thermal-electrical energy conversion. In this work, Sn-Se alloy core borosilicate glass-clad fibers with ∼94 μm core and ∼220 μm cladding in diameter were fabricated by a molten core drawing method. X-ray diffraction (XRD) showed the core to be highly crystalline and consist of SnSe and SnSe2 poly-crystal grains. Based on EPMA measurement, there exists an inter-diffusion process between the core and cladding ions during the fiber drawing. The Seebeck coefficient of the Sn-Se core is −151 μV/K. The electrical conductivity of the Sn-Se core is as high as 6.2 × 103 S/m, which is close to that of SnSe single crystals. The demonstration of fibers with TE core materials and the integration with the conventional fiber fabrication technique represents the first step in providing the building blocks for fiber-integrated TE devices.

Tm3+-doped lead-silicate glass with good thermal stability was prepared by the melt-quenching method. The absorption spectra, emission spectra, luminescent lifetime, and absorption and emission cross sections of the core glass were measured and analyzed. Then, Tm3+-doped lead-silicate glass photonic crystal fiber (PCF) was successfully drawn with a core diameter of $30~\mu \text{m}$ and a mode-field-area of ± $3160~\mu \text{m}^{2}$ of the emitted fundamental mode. Nearly 2.0- $\mu \text{m}$ amplified spontaneous emission was obtained in a 3.0-cm-long as-drawn PCF. The results indicate that the Tm3+-doped PCF is a promising fiber material for 2.0- $\mu \text{m}$ fiber laser applications.

In4Se3 exhibits high thermoelectric performance as a typical example of semiconductors, which is a promising thermoelectric candidate for energy conversion applications. Here, InSe alloy core thermoelectric fibers with glass cladding were fabricated by a reactive molten core drawing method. The as-drawn fiber core was found to be InSe crystals as evidenced by X-ray diffraction. The In4Se3 crystals were obtained in the fiber core by annealing the as-drawn fibers. The Seebeck coefficient of the In4Se3 core fibers (−347 μV/K) was enhanced by ∼85% compared with that of the as-drawn InSe core fibers (−189 μV/K). This work constitutes a proof-of-concept that thermoelectric materials can be incorporated into fibers, which have promising applications in fiber-based thermoelectric devices.

A new type of thermally sensitive fibers with an antimony selenide (Sb 2 Se 3 ) core and phosphate glass cladding is demonstrated. The fibers were fabricated by a molten core method and maintained overall diameters ranging from 250 to 800 μm and core diameters of 35–200 μm. A 2.8 cm long Sb 2 Se 3 core fiber, electrically contacted to external circuitry through fiber end facets, exhibited a four orders of magnitude change in conductivity after the whole fiber was heated from 25 to 195 °C. In addition, the fiber exhibited enhanced photoconductivity under illumination. These results indicate that Sb 2 Se 3 core multimaterial fibers have promising applications in temperature sensing, optical switches and photodetectors.

Highly rare earth ions (RE-ions) doping phosphate glass fiber makes it possible to obtain high gain and high output power per unit length. However, high concentrations of RE-ions will cause concentration quenching and crystallization during the conventional rod-in-tube fiber drawing process. In this work, highly Er 3 + /Yb 3 + co-doped multi-component phosphate glasses were prepared by the melt-quenching method. Through thorough investigation of 1.53 μm luminescent properties of the glasses, optimal RE-ions were ascertained. The Er 3 + and Yb 3 + doping concentrations reach as high as 13.77 × 10 20 and 2.295 × 10 20 ions/cm 3 , respectively. Then the silicate-clad highly Er 3 + /Yb 3 + co-doped phosphate core multimaterial fibers were successfully fabricated by a molten core method. The multimaterial fibers have a large refractive index difference and good interface between the phosphate glass core and silicate glass cladding. An intense 1.53 μm emission was obtained from the multimaterial fiber. The results indicate that the highly Er 3 + /Yb 3 + co-doped multimaterial fibers are promising in applications that require high gain and high power from a short piece of active optical fiber.

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.

Yb3 +/Tm3 + co-doped fluorogermanate glasses have been prepared by the melt-quenching method. Their luminescent properties were investigated by absorption spectra, excitation and emission spectra, and dynamic luminescence decay curves. The energy transfer parameters were analyzed by the phonon sideband theory and the energy transfer mechanism between Yb3 + and Tm3 + was proposed. An efficient 1.8 μm luminescence with reduced up-conversion emission is achieved under excitation of 980 nm laser diode. It is found that the emission at 800 nm is the main path of energy loss in the up-conversion process and it can be lowered at a higher Tm3 + doping level. In addition, the forward energy transfer parameter from Yb3 + to Tm3 + is approximately two orders of magnitude greater than the backward one, supporting efficient 1.8 μm emission.

Rare-earth (RE) doped photonic glasses exhibit potential applications in the area of optical communication, laser lidar, remote sensing, infrared detection, and biomedical. Up to now, the widely used silica based photonic glasses encounted intrinsic limitations such as lower rare-earth doping concentration, narrower emission band, larger phonon energy, and lower gain coefficients. Therefore, it is necessary to study and develop novel photonic glasses and fibers to meet the needs of new wavelength bands, especially the near-and mid-infrared materials and devices. In this paper, the important applications of RE doped photonic glasses in optical fiber amplifiers and fiber lasers are briefly described. The basic requirements for realizing near-and mid-infrared luminescence and laser are summarized. The latest research progress in RE doped photonic glasses, fibers, and devices are reviewed with special emphasis on 1.0, 1.5, 2.0 and 3.0 μm wavelength bands. In addition, challenges, applications, and future advances of the near-and mid-infrared luminescence and laser in RE doped photonic glasses have also been dealt with.

For the first time to the best of our knowledge phosphate glass-clad optical fibers comprising tellurium (Te) semiconductor core have been fabricated using a molten core approach. The cores were found to be highly crystalline and phase-pure as evidenced by X-ray diffraction (XRD) and corroborated by Micro-Raman spectrum. Elemental analysis across the core/clad interface suggests that there is some diffusion of oxygen and phosphorus into the core region and, conversely, diffusion of Te into the cladding region. Unfortunately, the propagation loss of the Te core fibers was too high to measure due to the significant scattering from the grain boundaries, oxygen and phosphor precipitates. However, the larger Raman gain, infrared and terahertz transparency of tellurium over silicon and germanium should make these fibers of significant value for fiber-based mid- to long-wave infrared, terahertz waveguides and Raman-shifted infrared light sources.

Elemental bismuth (Bi) exhibits a high magnetoresistance as a typical example of semimetal, which has significant application in information technologies. Silicate glass-clad Bi core fibers were fabricated by a molten core method and maintained core diameter of 100–150 µm and overall diameter of 300–450 µm. X-ray diffraction (XRD) and micro-Raman spectra showed the core to be highly crystalline with no observed secondary phases. Electro-probe micro-analyzer (EPMA) measurements confirmed a very well-defined core-clad interface. Demonstration of fibers with high magnetoresistance core materials and the potential integration with current state of the art technologies represents the first step in providing the building blocks for all-fiber sensors.

Transparent Er3+-doped germanotellurite glass ceramics (GCs) with variable Te/Ge ratio were prepared by controllable heat-treated process. X-ray diffraction (XRD) and transmission electron microscope (TEM) confirmed the formation of nanocrystals in glass matrix. Raman spectra were used to investigate the evolution of glass structure and photon energy. Fourier transform infrared (FTIR) spectra were introduced to characterize the change of hydroxyl group (OH−) content. Enhanced 2.7 μm emission was achieved from Er3+-doped GCs upon excitation with a 980 nm laser diode (LD), and the influence of GeO2 concentration and heat-treated temperature on the spectroscopic properties were also discussed in detail. It is found that the present Er3+-doped GC possesses large stimulated emission cross section at around 2.7 μm (0.85 × 10−20 cm2). The advantageous spectroscopic characteristics suggest that the obtained GC may be a promising material for mid-infrared fiber lasers.

In this work, Tm:YAG (Tm: Y 3 A l 5 O 12 ) ceramic-derived multimaterial fiber was fabricated by using the molten core method, which has a high gain per unit length of 2.7 dB/cm at 1950 nm. To our knowledge, this is the highest gain per unit length at 2 µm band in similar Tm:YAG-derived multimaterial fibers. A distributed Bragg reflector (DBR) fiber laser was built based on a 10-cm-long as-drawn fiber. The achieved 1950 nm laser, which has a maximum output power of ∼ 240 m W and a slope efficiency of 16.5%, was pumped by a self-developed 1610 nm fiber laser. What is more, an all-fiber-integrated passively mode-locked fiber laser based on the 10-cm-long as-drawn fiber was realized. The mode-locked pulses operate at 1950 nm with duration of ∼ 380 p s , and the repetition rate is 26.45 MHz. The results described here indicate that the Tm:YAG ceramic-derived multimaterial fiber with high gain per unit length has promising applications in 2 µm all-fiber fiber lasers.

The competition between infrared down-conversion (DC) and visible up-conversion (UC) is systemically studied in Tm3 + and/or Yb3 +/Tm3 + co-doped fluoride modified germanate glasses. Based on the absorption spectra, the Judd–Ofelt intensity parameters, absorption and emission cross-sections, figure of merit (FOM), and saturated gain coefficient are calculated and analyzed. An intense 1.8 μm emission is obtained upon 808 nm laser diode (LD) excitation in Tm3 + doped samples, while an efficient 1.8 μm emission is observed by 980 nm LD in Yb3 +/Tm3 + co-doped samples, along with visible UC emissions. It is found that 3F4 state of Tm3 + can be easily populated and then further excited to higher excited states through Yb3 + upon 980 nm LD. Our results suggest that these Tm3 + doped fluoride modified germanate glasses are of great significance for searching efficient mid-infrared laser materials.

Enhanced 1.8 μm emission from Tm 3+ by Yb 3+ sensitization and bubbling in tungsten tellurite glasses has been demonstrated under the excitation of a 976 nm laser diode. Radiative properties such as spontaneous emission probabilities, radiative lifetimes and fluorescence branching ratios along with absorption and emission cross sections have been calculated from the absorption spectra. The influences of Yb 3+ concentration, Tm 3+ concentration, and bubbling time on spectroscopic properties have been thoroughly investigated. It is found that with increasing the bubbling time to 35 min, OH − content deceases sharply while 1.8 μm emission intensity improves greatly and 3 F 4 level lifetime prolongs to 1.57 ms close to radiative time. After 35 min, they change very little due to almost reaching the dynamic balance. The strength of interaction between Tm 3+ and OH − is determined. The energy transfer mechanism between Yb 3+ and Tm 3+ is proposed by photoemission spectroscopy and lifetime measurement. The energy transfer coefficients have been analyzed by the extended spectral overlap method and hopping model. Large ratio of the forward energy transfer from Yb 3+ to Tm 3+ to the backward one (223) and high energy transfer efficiency (97%) from Yb 3+ to Tm 3+ ensure efficient 1.8 μm emission. Hence, Yb 3+ sensitization and the reduction of OH − content could be expected to open up a possibility to achieve high efficient 2.0 μm lasing from Tm 3+ under a 976 nm LD pump.

ZnO–TeO2–P2O5 glasses were prepared by melt-quenching method. The color of the glass samples changed from colorless to pale red and dark red with increasing TeO2 content. Coloration mechanism and nonlinear optical properties of ZnO–TeO2–P2O5 glasses have been investigated. Raman spectra and transmission electron microscope measurements indicated the precipitation of ZnTe quantum dots in the glasses and ZnTe quantum dots are the origin of coloration. Z-scan technique was used to examine the nonlinear optical properties of the glasses. The glass sample with 30 mol% TeO2 exhibits large third-order nonlinear optical susceptibility of 10−11 esu.

Transparent Er3+-doped germanotellurite glass ceramics (GCs) with variable Te/Ge ratio were prepared by controllable heat-treated process. X-ray diffraction (XRD) and transmission electron microscope (TEM) confirmed the formation of nanocrystals in glass matrix. Raman spectra were used to investigate the evolution of glass structure and photon energy. Fourier transform infrared (FTIR) spectra were introduced to characterize the change of hydroxyl group (OH−) content. Enhanced 2.7 μm emission was achieved from Er3+-doped GCs upon excitation with a 980 nm laser diode (LD), and the influence of GeO2 concentration and heat-treated temperature on the spectroscopic properties were also discussed in detail. It is found that the present Er3+-doped GC possesses large stimulated emission cross section at around 2.7 μm (0.85 × 10−20 cm2). The advantageous spectroscopic characteristics suggest that the obtained GC may be a promising material for mid-infrared fiber lasers.

The laser performance of Er3+-doped tellurite fiber lasers operating at 2.7 μm due to 4I11/2 → 4I13/2 transition has been theoretically studied by using rate equations and propagation equations. The effects of pumping configuration and fiber length on the output power, slope efficiency, threshold, and intracavity pump and laser power distributions have been systematically investigated to optimize the performance of fiber lasers. When the pump power is 20 W, the maximum slope efficiency (27.62%), maximum output power (5.219 W), and minimum threshold (278.90 mW) are predicted with different fiber lengths (0.05–5 m) under three pumping configurations. It is also found that reasonable output power is expected for fiber loss below 2 dB/ m. The numerical modeling on the two- and three-dimensional laser field distributions are further analyzed to reveal the characteristics of this multimode step-index tellurite fiber. Preliminary simulation results show that this Er3+-doped tellurite fiber is an excellent alternative to conventional fluoride fiber for developing efficient 2.7 μm fiber lasers.

The morphology of hexagonal phase NaYF4:Er3+ nanorods synthesized by hydrothermal method changed greatly after a continuing calcination, along with a phase transformation to cubic phase. Photoluminescence (PL) spectra indicated that mid-infrared (MIR) emission was obtained in both hexagonal and cubic phase NaYF4:Er3+ nanocrystals for the first time. And the MIR emission of NaYF4:Er3+ nanocrystals enhanced remarkably at higher calcination temperature. To prevent uncontrollable morphology from phase transformation, the cubic phase NaYF4:Er3+ nanospheres with an average size of ~100 nm were prepared via a co-precipitation method directly. In contrast, the results showed better morphology and size of cubic phase NaYF4:Er3+ nanocrystals have realized when calcined at different temperatures. And PL spectra demonstrated a more intense MIR emission in the cubic phase NaYF4:Er3+ nanocrystals with an increasing temperature. Besides, the MIR emission peak of Er3+ ions had an obvious splitting in cubic phase NaYF4. Therefore, cubic phase NaYF4:Er3+ nanospheres with more excellent MIR luminescent properties seems to provide a new material for nanocrystal-glass composites, which is expected to open a broad new field for the realization of MIR lasers gain medium.