Xusheng Wang

Bright dual-mode green emission and temperature sensing properties in Er3+/Yb3+ co-doped MgWO4 phosphor

Er3+/Yb3+ co-doped MgWO4 phosphor was synthesized by a solid state reaction method and the phase, photoluminescence and temperature sensing properties were analyzed. The phosphor has shown intense visible green emission via up-conversion process on near-infrared (980 nm) excitation and down-conversion process on 379 nm excitation and thus behaves as a dual-mode phosphor. In the up-conversion and down-conversion emission, the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of the Er3+ ion portray a temperature dependent behavior and have been used for optical temperature sensor by means of the fluorescence intensity ratio method. Moreover, we compared the curves of S in the continuous temperature range (83–583 K) and the two sectional temperature ranges in up-conversion process. It is found that the phosphor can be operated over a temperature range of 83–583 K with a maximum sensitivity of about 0.0093 K−1 at 583 K. The results indicate that the Er3+/Yb3+ co-doped MgWO4 phosphor is a potential candidate to be used in display devices and optical temperature sensors.

Color-tunable upconversion photoluminescence and highly performed optical temperature sensing in Er 3+ /Yb 3+ co-doped ZnWO 4 .

Er3+/Yb3+ co-doped ZnWO4 phosphors were synthesized by a solid state reaction method and their structure, photoluminescence and temperature sensing properties were characterized. The color-tunable upconversion emissions (from green to red) were observed by increasing the doped Er3+/Yb3+ concentration. The temperature sensing properties were studied by using the fluorescence intensity ratio technique in the temperature range of 83-583 K, and high performance was obtained. The maximum sensitivity is found to be 0.0099 K-1 at 583 K. The XRD Rietveld refinement revealed that the phosphors crystallized in monoclinic structure with the space group P2/c (13) at room temperature. The results suggest that the phosphors could be an exceptional choice for next generation luminescence-based temperature sensing devices as well as in multiple biolabels.

Phase Transitions and Relaxation Behaviors in Barium Strontium Titanate Ceramics Determined by Dynamic Mechanical and Dielectric Analysis

Barium strontium titanate (Ba1-xSrxTiO3) ceramics were prepared by solid-state reaction method. XRD patterns showed that BT (x = 0) and BST2 (x = 0.2) ceramics presented tetragonal phase, while BST4 (0.4) and BST6 (0.6) ceramics showed cubic phase at room temperature. The relative permittivity and dissipation factor of Ba1-xSrxTiO3 ceramics with temperature of 125–425 K were characterized at 1–100 kHz by LCR meter. The Youngs modulus and internal friction of Ba1-xSrxTiO3 ceramics in the range of 125 K–425 K at different vibration frequencies were tested by a Dynamic Mechanical Analysis (DMA) system. Compared with the dielectric measurement, mechanical analysis was more sensitive to reflect the phase transition and relaxation process. All Ba1-xSrxTiO3 samples showed three phase transitions, the transition temperatures decreased and the phase transition diffused as Sr content increased. Besides, a relaxation process caused by the interaction between domain walls and lattice defects emerged in pure BT ceramic, while it disappeared in all BST ceramics.

Upconversion luminescence and temperature-sensing properties of Ho3+/Yb3+-codoped ZnWO4 phosphors based on fluorescence intensity ratios

Ho3+/Yb3+-codoped ZnWO4 phosphors were synthesized using a solid state reaction method and their structures, upconversion (UC) luminescence, and temperature-sensing properties were investigated. The obtained ZnWO4:0.01Ho3+/xYb3+ phosphors crystallized in the monoclinic phase with space group P2/c. Under 980 nm excitation, bright green [(5F4, 5S2) → 5I8], weak red (5F5 → 5I8), and near-infrared emissions [(5F4, 5S2) → 5I7] were observed. The optimal Ho3+ and Yb3+ doping concentrations in ZnWO4 were 0.01 and 0.15, respectively. The near-infrared-green (I757/I540) and red-green (I641,665/I540,549) fluorescence intensity ratios (FIRs) were studied as a function of temperature at 83–503 K. The sensitivity of the ZnWO4:0.01Ho3+/0.15Yb3+ phosphors was also discussed and their potential application as thermal sensors in luminescence thermometry was analyzed using a four-level system and the intensity ratio of the red and green emissions. ZnWO4:0.01Ho3+/0.15Yb3+ phosphors could potentially be applied as optical temperature-sensing materials.

Green and Red Up-Conversion Luminescence of Er3+/Yb3+ Co-Doped 0.94Na0.5Bi0.5TiO3-0.06 BaTiO3 Ceramics

The Er3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Er3+/Yb3+) cera-mics were synthesized by a traditional solid state reaction method. The XRD patterns show that all the ceramics are the single phase with perovskite structure. Under the excitation of 980 nm laser diode, the samples exhibit bright green up-conversion (UC) emission bands, which corresponds to the radiative transitions from (4S3/2,2H11/2) to 4I15/2, respectively. By tailoring the ratio of Er3+/Yb3+, the optimal UC emission properties were obtained in NBT-BT:0.01Er, 0.10Yb ceramics. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0040K−1 at 502K. Moreover, ferroelectric and dielectric properties were enhanced with small amount of Er3+/Yb3+ co-doped. These ceramics, with excellent properties, may be a potential candidate in the application for electro-optical devices.

Up-conversion Luminescence, Temperature Dependence and Ferroelectric Properties in Ho3+ and Yb3+ Co-Doped Bi3TiNbO9 Multifunctional Ceramics

Bi3TiNbO9 (BTN) is an important member of the Aurivillius bismuth layer-structured ferroelectric compounds, consisting of [Bi2O2]2+ layers between which [BiTiNbO7]2- layers are inserted. Ho3+ and Yb3+ co-doped Bi3TiNbO9 (BTN) ceramics were synthesized by a conventional solid state reaction method and their up-conversion (UC) luminescence and the ferroelectric properties were investigated. A strong green emission band centered at 547 nm, two weak red emission bands centered at 657 nm and 758nm were obtained under a 980 nm laser excitation at room temperature. With the increasing of Yb3+ content, the intensity of the up-conversion luminescence increased initially and then decreased due to concentration quenching. The fluorescence intensity ratio of green UC emission centered at 547 nm and red UC emission centered at 657 nm was studied as a function of temperature in a range of 123 - 573K, and the result showed a quite good linear variation of the two emissions with temperature, which indicates that Ho3+/Yb3+ co-doped Bi3TiNbO9 multifunctional ceramic is a promising candidate for applications in optical temperature sensors.

Broadband Near-Infrared Photoluminescence and Strong Visible Up-Conversion Emission in BaTiO3-(Na0.5Er0.5)TiO3 Lead-Free Piezoelectric Ceramics

For checking photoluminescence properties of BaTiO3-(Na0.5Er0.5)TiO3 lead-free piezoelectric ceramics, optical diffuse reflection spectra, visible up-conversion luminescence spectra, 1.55 μm near-infrared photoluminescence spectra, and optical temperature sensing performances under the excitation of 980 nm laser were investigated systematically. Broadband near-infrared (˜1.55 μm, FWHM˜90 nm) emission and strong visible up-conversion (˜550 nm) emission were observed under the 980 nm excitation in the ceramics at room temperature. Near-infrared emission and visible up-conversion emission became stronger with increasing (Na0.5Er0.5)TiO3 concentration below quenching point above which it will degrade. The optimal emission intensity was obtained when (Na0.5Er0.5)TiO3 content was 7 mol%. These ceramics with excellent ferro-/piezoelectric and photoluminescence properties may be useful for ultrasonic transducer, optical temperature sensor, optical amplifier, and other relative applications.

Bright Green Emission in Ho+3-Yb+3 Co-Doped Bi1/2Na1/2TiO3 Ferroelectric Ceramics and the Optical Thermometry Behavior

Ho+3-Yb+3 co-doped bismuth titanate ferroelectric ceramics were prepared by the solid-state reaction method. A bright green emission is observed at room temperature, which ascribed to 5F4+5S2 →5I8 transition. The dependence of the emission intensity on the pumping power indicated that the up-conversion emission in the ceramics was a two-photon process. Additionally, an optical temperature sensor based on the blue emission from the 5F2,3/3K8 and 5F1/5G6 states of Ho3+ ions has been developed. In the temperature range of 273–573 K, the maximum sensitivity of about 0.0009 K−1is obtained. Our study suggests that Ho3+ and Yb3+ co-doped Bi1/2Na1/2TiO3 (NBT) ceramics can be applied to the fabrication of new photoluminescence ferroelectric ceramics devices and of the optical temperature sensors.

Fatigue Behaviors in PZT Ceramics Induced by Mechanical Cyclic Load

The PZT-5H and PZT-8 ceramics were subjected to fatigue testing at room temperature by dynamic mechanical analysis (DMA) in different load cycles. The elastic modulus of each sample showed fatigue-free character after 7 × 107 load cycles. The number of mechanical load cycles at which the onset of fatigue in ferroelectric and piezoelectric properties occurred was 107 load cycles for both PZT ceramics. The crystal structure and internal stress were soon analyzed by XRD before and after mechanical load cycles. The results prove that, the domain wall moved and the internal stress increased in PZT samples after mechanical load cycles.

Photoluminescence and thermal stability of yellow-emitting Pr3+ doped CaAl2O4 phosphors

Pr3+-doped CaAl2O4 phosphors with broad yellow emission were synthesized by conventional solid-state reaction in air and their structural and luminescent properties were investigated. A pure monoclinic structure can be obtained when the sintering temperature is 1400°C or above. With photoluminescence (PL) measurement, the excitation was observed at 450–500 nm, which covered the emission of the blue light-emitting diode (LED) chips. Emission of the phosphors showed a green band and a red band. So these phosphors showed great potential in application of warm white LEDs without reabsorption. Additionally, the optimal emission intensity was obtained when Pr doping level was at 0.2 mol%. Furthermore, the Pr-doped CaAl2O4 phosphors have the higher quenching temperature. With an increase in temperature, the emission bands of Pr-doped CaAl2O4 showed an abnormal blue-shift.