Li Meiling,Cao Yongze,Cheng Lihong,Fan Yuhan,Wang Yichao,Li Xiangping,Zhang Xizhen,Chen Baojiu
A series of Er 3+ /Yb 3+ co-doped NaY(WO 4 ) 2 (NYWO) phosphors are prepared by molten salt synthesis (MSS) with Na 2 SO 4 as solvent. The holding temperature, holding time, and solvent-to-solute mass ratio parameters are regulated. The structure, morphology, and luminescence properties of the samples were tested by XRD, SEM, and fluorescence spectrometers, respectively. The lamellar sample is prepared at 900℃ for 5 h when solvent-to-solute is 3, which has the highest pure green upconversion luminescence (UCL) intensity under 980 nm laser excitation. It is demonstrated that the UCL intensity of the samples prepared by MSS is higher than that of solid sintered samples. The maximum absolute sensitivity (S A ) and relative sensitivity (S R ) are 0.012184 K⁻ 1 at 507 K and 0.01102 K⁻ 1 at 303 K, respectively. These materials can be used for pure green luminescence displays and temperature sensing.
Yao Hanyu,Shen Honglie,Tang Quntao,Yang Nannan,Zhai Zihao,Li Yufang
NaY(WO 4 ) 2 : Er 3+ phosphors with various doping concentrations of [Er 3+ ]/([Er 3+ ]+[Y 3+ ]) (0, 5, 7, 10, 12, 15%) were successfully synthesized by high-temperature solid-state reaction. X-ray diffraction (XRD) measurement demonstrated the presence of tetragonal-phase NaY(WO 4 ) 2 phosphors and Fourier transform infrared (FT-IR) spectra showed a strong υ 3 stretching vibration mode of WO 4 2− , indicating the good crystallization of the phosphors. Well-crystallized phosphors showed a fine morphology with particle sizes of 0.8–10 µm by scanning electron microscope (SEM). Under excitation of 980 nm laser, Er 3+ -doped phosphors exhibited strong green emissions centered at 527 and 549 nm in addition to a 665 nm emission band in the red region, which were assigned to the 2 H 11/2 , 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions, respectively. When the doping concentration was 10%, the intensities of green and red emissions reached their maximum values, stronger than that in 5% Er 3+ doped one by 13 times. The double-logarithm plot of the upconversion (UC) emission intensity to the excitation power for different Er 3+ doping concentrations depicted that at least two infrared photons were involved for every emitted green and red photon. UC emission intensity changing with temperature displayed different trends for the phosphors with different Er 3+ concentrations. The enhancement for green emission band centered on 549 nm could reach 50 times at 30 K in sample with 5% Er 3+ concentration. Under excitation by 355 nm laser, all the phosphors showed a strong PL emission band at 430 nm, while green luminescence band locating from 540 to 570 nm was only observed in 7, 10, and 12% Er 3+ -doped phosphors, which was ascribed to 4 S 3/2 → 4 I 15/2 transition.
Hanyu Yao,Honglie Shen,Quntao Tang,Jiaqi Peng,Rui Liu
The fluorescence-based temperature sensor using temperature-dependent fluorescence properties is a great candidate to replace traditional temperature-measurement detector like thermocouple , because the latter is inaccessible to conquer some special circumstances such as a corrosive environment. In this study, the nano-sized Er 3+ doped NaY(WO 4 ) 2 phosphors were synthesized by solvothermal method. The origins of three emission peaks located at 527 nm, 549 nm and 665 nm were identified. The 2 H 11/2 → 4 I 15/2 (green emission 1) and 4 S 3/2 → 4 I 15/2 (green emission 2) transitions of the Er 3+ ion possessed a temperature dependent behavior over the range of 300–30 K and it was proposed for temperature sensing (optical thermometry) using the fluorescence intensity ratio (FIR) method. The FIR value of nano-sized phosphors decreased with the decrease of temperature, and the experimental data were well fitted with a theoretical function. A large energy difference (1048.5) was obtained from the fitting curve, which indicate that the sensitivity of nano-sized NaY(WO 4 ) 2 : Er is higher than that of micro-sized one prepared by high temperature solid state reaction. Particularly, at temperatures below 150 K, the sensitivity of nano-sized UC phosphors was enhanced obviously. The results suggested that this nano-sized phosphor could be a splendid option for next generation luminescence-based temperature sensing devices in cryogenic region.
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