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A highly sensitive and flexible, multichannel thermometer prepared by exploiting the emission behaviors of Er3+ in Y7O6F9:Er/Yb crystal-embedded polyacrylonitrile fibers is reported. This sensor could be operated at 303–433 K, and the maximum relative sensitivity based thermal-coupling level was 1.285% K−1 at 303 K. More interesting is that the self-calibration could be achieved from the single Er3+ emission avoiding the intervention of other calibration tools. Repeatability experiments also confirmed the accuracy and durability of this fabricated material. Further details have been provided to reveal the multi-channel sensing mechanism, in which the green–green emission and red–red emission based thermal-coupling level, and the blue-green emission based non-thermal coupling level are discussed. All the above results showed that the Y7O6F9:Er/Yb crystal-embedded polyacrylonitrile fibers have extraordinary potential in intelligent wearable devices, industrial safety protection, and anti-counterfeiting mark fields. [ABSTRACT FROM AUTHOR]

Sr2(La1−xErx)F7/polyacrylonitrile composite fibers with special pliability and excellent crystal dispersibility have been fabricated, which provide smaller size and appropriate temperature sensitivity. Up-conversion emission shows quadratic dependence of the photoluminescence intensity on pump power, confirming the participation of two photons during the excitation processes. The composite fibers, combining main and auxiliary sensing derived from green and red emissions, give fibers the ability to obtain accurate results and better reproducibility. Among them, assigning the green emission as the main indicator of non-contact temperature sensing, the absolute and relative sensitivities are 0.514% K−1 and 0.654% K−1 at 373 K, respectively. Furthermore, the ratio of green and red emission serves as an auxiliary monitoring parameter to calibrate the deviation, where the absolute and relative sensitivities reach 7.208% K−1 and 0.901% K−1 at 373 K. In general, composite fibers with excellent dual-ratiometric temperature sensing are expected to be applied in biological probes, miniature devices and accurate temperature sensors. [ABSTRACT FROM AUTHOR]

Composition effect on electro-optic (EO) properties of a LiNbO3 (LN) single-crystal has been investigated in a Li2O-content range of 47.0-49.95 mol%. Some non-congruent LN crystals with different Li2O-contents were prepared by performing Li-deficient or Li-rich vapour transport equilibration treatments on as-grown congruent LN crystals. Unclamped EO coefficients γ13 and γ33 of these samples were measured by a Mach-Zehnder interferometric method. The measurements show that in the Li-deficient regime both γ13 and γ33 increase by ~8% as Li2O-content decreases from the congruent 48.6 mol% to the 47.0 mol% in the Li-deficient regime. The feature is desired for the EO application of the Li-deficient crystal. In the near-stoichiometric regime, both γ13 and γ33 reveal a non-monotonic dependence. As the Li2O-content increases from the 48.6 mol%, the EO coefficient decreases. Around Li2O-content 49.5 mol%, a minimum is reached. After that, the EO coefficient recovers slowly. At the stoichiometric composition, it recovers to a value close to that at the congruent point. Comparison shows that different crystal growth methods give rise to different defect structure features and hence different composition effects. [ABSTRACT FROM AUTHOR]

Abstract: Efficient infrared emissions at ~ 1.2 and ~ 2.0 µm were recorded in Ho3+-single-doped and Ho3+/Yb3+-co-doped aluminum germanate glasses (NMAG), respectively. The maximum stimulated emission cross-sections for the ~ 1.2- and ~ 2.0 µm emissions were derived to be 2.3 × 10−21 and 5.8 × 10−21 cm2, respectively; then the gain cross-sections were further evaluated and the effective gains have been anticipated. In addition, the channel waveguide fabricated by K+-Na+ ion-exchanged method exhibited a complete single mode at 1.55 µm and the field diameters were identified to be horizontally 10.6 µm and vertically 6.7 µm. Effective amplified spontaneous emission at ~ 2.0 µm was recorded under 980 nm laser pumping. Broad bandwidth, large emission cross-section and perfect thermal ion-exchangeability indicate that Ho3+- and Yb3+-doped NMAG glasses are promising for the development of optical amplifier, tunable laser and light source operating at ~ 1.2 and ~ 2.0 µm.Graphical abstract: [ABSTRACT FROM AUTHOR]

Sm3+ doped germanotellurite glasses (NZPGT) with maximum phonon energy of 793cm−1 have been prepared and characterized. Judd-Ofelt parameters Ωt (t=2, 4, 6) have been calculated to be 3.52×10−20, 4.70×10−20 and 1.90×10−20cm2, respectively. Large value of Ω2 indicates a high asymmetry and covalent environment around Sm3+ in the glass system. The maximum stimulated emission cross-section of the dominant transition 4G5/2→6H9/2 peaking at 645.0nm was derived to be 10.00×10−22cm2, predicting that the red fluorescence emission can be efficiently extracted from the optical glasses. The internal quantum efficiency and external quantum yield of 0.4wt% Sm2O3 doped NZPGT glasses were deduced to be 82.5% and 6.0%, respectively. The results demonstrate that Sm3+ doped NZPGT glasses are a potential candidate for developing tunable visible lasers, compact light sources and solid-state display devices. [ABSTRACT FROM AUTHOR]

Sr 2 (La 1- x Er x )F 7 /polyacrylonitrile composite fibers with special pliability and excellent crystal dispersibility have been fabricated, which provide smaller size and appropriate temperature sensitivity. Up-conversion emission shows quadratic dependence of the photoluminescence intensity on pump power, confirming the participation of two photons during the excitation processes. The composite fibers, combining main and auxiliary sensing derived from green and red emissions, give fibers the ability to obtain accurate results and better reproducibility. Among them, assigning the green emission as the main indicator of non-contact temperature sensing, the absolute and relative sensitivities are 0.514% K -1 and 0.654% K -1 at 373 K, respectively. Furthermore, the ratio of green and red emission serves as an auxiliary monitoring parameter to calibrate the deviation, where the absolute and relative sensitivities reach 7.208% K -1 and 0.901% K -1 at 373 K. In general, composite fibers with excellent dual-ratiometric temperature sensing are expected to be applied in biological probes, miniature devices and accurate temperature sensors.

Multi-photon-excited thermal-correlated green and red upconversion (UC) emissions have been quantified in H o 3+ / Y b 3+ co-doped fluotellurite (BZLFT) glass phosphor under the 978 nm laser excitation. The temperature dependence of the fluorescence intensity ratio (FIR) originated from UC emissions bands centered at 550 nm and 661 nm has been verified in the range of 303-543 K. The net emission photon numbers of 5 F 4 + 5 S 2 → 5 I 8 and 5 F 5 → 5 I 8 transition emissions are up to 40.08×10 12 and 68.51×10 12 c p s in the 0.4 w t . % H o 2 O 3 -0.4 w t . % Y b 2 O 3 co-doped BZLFT case under the 6.95 W / m m 2 laser power density. Furthermore, the quantum yield (QY) and luminous flux are determined to be dependent on pumping power. When the excitation power increases 874 mW, the QY values for 550 nm and 661 nm emissions are as high as 0.94×10 -5 and 1.60×10 -5 . In addition, the high photon producing efficiency is conducive to ensuring high feedback to thermosensitive performance. The temperature thermal sensor can be manipulated steadily in medium temperature range, and the relative sensitivity reaches 0.4 % K -1 at 303 K, which is 1 order of magnitude larger than those in several rare-earth-doped materials. Efficient photon conversion ability and high temperature sensitivity indicate that the rare-earth-ion-doped fluotellurite material has a prospective application in the construction of optical temperature sensors based on the FIR technique allowing for self-referenced temperature determination.

Intense multi-peak red fluorescence and effective near-infrared (NIR) ultra-broadband emission have been observed in Pr 3+ doped ion-exchangeable aluminum germanate (NMAG) glasses. The maximum emission cross section for P 0 3→F 2 3 red emission is up to 100.58×10 -21   cm 2 , and the NIR emission corresponding to D 2 1→G 4 1 transition possesses a full-width at half-maximum (FWHM) of 210 nm. Although the obvious cross-relaxation (CR) process at high concentration causes a decrease of the quantum efficiency, the CR broadens the spectral FWHM effectively from another perspective. The admirable red fluorescence trace and the NIR single-mode transmission confirm that Pr 3+ doped NMAG glass planar waveguides can support the generation of visible fluorescence and the amplification of infrared signal. For a waveguide channel ion-exchanged in molten KNO 3 for 2 h, the single-mode field diameters at 1.55 μm are identified to be 10.4 μm in the horizontal direction and 6.5 μm in the vertical direction, implying an acceptable overlap with a standard single-mode fiber. Effective red fluorescence and broad NIR emission demonstrate that Pr 3+ doped NMAG glasses are a promising substrate in developing irradiative luminescence sources and ultra-broadband waveguide amplifiers, especially operating at the entire S-, C-, and L- bands.