Yan Cui,Yan Gao,Zhichao Meng,Tao Hu,Yeqing Chen,Yan Chen,Qingguang Zeng
Optical thermometry offers promising applications in the fields of microelectronics and biomedicine, as well as in fire pre-warning systems. In this research, Pr3+-activated SrZn0.33Nb0.67O3 phosphors were successfully prepared via solid-state reactions. Under ultraviolet excitation, the SrZn0.33Nb0.67O3:x%Pr3+ (x = 0.25/0.75/1.25/2) phosphors exhibit bright blue and red emissions, located at 491 nm (3P0 → 3H4), 619 nm (1D2 → 3H4) and 651 nm (3P0 → 3F2). Specifically, two fluorescence intensity ratio (FIR) models of 1D2 → 3H4versus3P0 → 3H4 (Red1/Blue) and 1D2 → 3H4versus3P0 → 3F2 (Red1/Red2) in the temperature range of 300–500 K are adopted for temperature sensing. Our results show that the designed phosphor can serve as a novel potential self-calibrated optical thermometer. Moreover, the temperature sensitivity of the FIR thermometer is significantly enhanced when Ga3+ is incorporated into the SrZn0.33Nb0.67O3. Specifically, the maximum absolute and relative sensitivity for the 6% Ga3+ co-doped sample are increased five- and two-fold, respectively, compared with the undoped sample. This work may provide useful inspiration for effectively improving the temperature-sensing performance of optical thermometers.
Kaidi Gao,Qiao Hu,Yu Xia,Guangming Han,Jianfeng Yao
NASICON-type Na 3 V 2 (PO 4 ) 3 (NVP) has been identified as an ideal cathode for sodium-ion batteries (SIBs) because of its ultra-fast Na + diffusion and very stable structure. However, it still suffers from significant problems such as a low operating voltage plateau (3.4 V, vs. Na + /Na), inferior electronic conductivity and unsatisfactory energy density (370 Wh kg −1 ), thereby hampering the commercialization of NVP. Herein, a series of Al 3+ /Ga 3+ co-doping Na 3 V 2 (PO 4 ) 3 cathodes were successfully prepared through a facile solid-state reaction process. The substitution of Al 3+ /Ga 3+ for V 3+ in Na 3 V 2–2x Al x Ga x (PO 4 ) 3 ( x = 0, 0.1 and 0.2) effectively activates the electrons outside of V and achieves an extra redox couple V 4+ /V 5+ for high-voltage (3.9 V, vs. Na + /Na) reactions. Moreover, the presence of Ga in this series of electrode materials increases the proportion of sp 2 -type carbon. The optimized Na 3 V 1.8 Al 0.1 Ga 0.1 (PO 4 ) 3 material possesses high ionic/electronic conductivity and superior electrochemical performance: the energy density is enhanced by approximately 13.1 % at 0.1 C (from 345.4 Wh kg −1 for NVP to 390.7 Wh kg −1 for Na 3 V 1.8 Al 0.1 Ga 0.1 (PO 4 ) 3 ), and the power density is increased by approximately 135 % at 30 C (from 2574 W kg −1 for NVP to 6039 W kg −1 for Na 3 V 1.8 Al 0.1 Ga 0.1 (PO 4 ) 3 ). Furthermore, Na 3 V 1.8 Al 0.1 Ga 0.1 (PO 4 ) 3 exhibits excellent cycling stability with 93.4 % capacity retention after 350 cycles at 1 C. Ex-situ XPS and electrochemistry investigations imply the high reversibility of the V 3+ /V 4+ /V 5+ redox reaction in Na 3 V 1.8 Al 0.1 Ga 0.1 (PO 4 ) 3 . This work proposes a novel strategy to modulate the electronic structure of NVP by co-doping with Al 3+ and Ga 3+ to achieve reversible multi-redox activity (V 3+ /V 4+ /V 5+ ) in NASICON-type NVP, thus providing a viable approach for advancing ultrafast high-energy sodium storage.
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