Yanxia Li

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.

Intensive up-conversion photoluminescence of Er3+-doped Bi7Ti4NbO21 ferroelectric ceramics and its temperature sensing

The intensive up-conversion (UC) photoluminescence and temperature sensing behavior of Er3+-doped Bi7Ti4NbO21(BTN) ferroelectric ceramics prepared by a conventional solid-state reaction technique have been investigated. The X-ray diffraction and field emission scanning electron microscope analyses demonstrated that the Er3+-doped BTN ceramics are single phase and uniform flake-like structure. With the Er3+ ions doping, the intensive UC emission was observed without obviously changing the properties of ferroelectric. The optimal emission intensity was obtained when Er doping level was 15 mol.%. The temperature sensing behavior was studied by fluorescence intensity ratio (FIR) technique of two green UC emission bands, and the experimental data fitted very well with the function of temperature in a range of 133–573 K. It suggested that the Er3+-doped BTN ferroelectric ceramics are very good candidates for applications such as optical thermometry, electro-optical devices and bio-imaging 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.

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.

Elastico-mechanoluminescence in non-piezoelectric CaTiO 3 :Pr 3+

Pure phase orthorhombic CaTiO₃:Pr³⁺ was synthesized by a conventional solid-state method and its elastico-mechanoluminescence (EML) was characterized. The results revealed that the EML emission peak was centered at 612 nm, similar to its photoluminescence (PL) (Fig.1), indicating both EML and PL originated from ¹D₂-³H₄ transitions of Pr³⁺. Thermoluminescence and afterglow properties showed tunneling effect in its anomalous fading. The EML mechanism of CaTiO₃:Pr³⁺ was discussed and thought to be attribute to tunneling effect instead of piezoelectricity. Lattice distortion caused by strain diminished the distance between electron captured by trap and Pr⁴⁺, and thus increased the probability of immigration of electron to Pr⁴⁺, eventually leading to EML.

Improved electrical properties and dual-mode photoluminescence in (1−x)(Na 0.475 K 0.475 Li 0.05 )NbO 3−x (Er 0.5 Na 0.5 )TiO 3 lead-free multifunctional ceramics

(1-x)(Na0.475K0.475Li0.05)NbO3-x(Er0.5Na0.5)TiO3 (0≤x≤0.025) lead-free multifunctional ceramics were prepared by a conventional solid-state reaction method. Their phase, photoluminescence, dielectric, ferroelectric and piezoelectric properties were investigated systematically by the X-ray Diffraction (XRD), scanning electron microscopy (SEM) spectrophotometer and electrical property measurements. The relationship of composition, microstructure and electrical properties and the mechanisms of up-conversion and down conversion emissions were analyzed detailed. The results show that the ceramics exhibit the optimum piezoelectric and ferroelectric properties when their compositions lie at the nearby of the morphotropic phase boundary (MPB). Moreover, these ceramics can emit strong 550 nm green light when they were excited by a nearinfrared (980 nm) light and a 486 nm blue light, respectively. Together with the excellent ferroelectric properties and good dielectric properties, these ceramics should be one of the promising candidates for multifunctional optoelectronic applications.