Weichang Li,Qiang He,Jixi Xu,Chongyun Shao,Shiyu Sun,Shaohua Fan,Lili Hu
The efficient NIR-to-NIR upconverter of LiYF 4 :Yb 3+ ,Tm 3+ (simplified as LYF:Yb,Tm) was synthesized by a modified hydrothermal method in this work. The synthesized LYF:Yb,Tm has well controlled morphology of monodisperse micrometer sized octahedrons. XRD pattern confirms its pure tetragonal LiYF 4 structure. The LYF:Yb,Tm exhibits a dominating NIR UC emission at ~793 nm along with relative weak blue and red UC emissions under 976 nm LD excitation. The optimal concentrations of Yb 3+ and Tm 3+ ions for NIR up-conversion (UC) emission are 20 mol% and 0.6 mol%, respectively. The internal UC quantum yield (IUCQY) of this LYF:Yb,Tm in NIR band is tested to be 5.1% at 959 nm LD excitation power density (PD) of 120 W/cm 2 . The UC emission mechanism is discussed based on UC fluorescent behaviors of Yb 3+ and Tm 3+ . The results of fluorescent labeling indicate its potential applications in fluorescent markers, solar cells and 3D flat panel displays .
Optical thermometry is a non-contact temperature detective technique that has high sensitivity and rapid response. In present work, we developed LiYF 4 :20Yb 3+ , 1Ho 3+ (mol%) micro octahedrons obtained by a modified hydrothermal method . The temperature dependent up-conversion (UC) emission and luminescence decays for LiYF 4 :20Yb 3+ , 1Ho 3+ under 976 nm LD excitation with various power density were studied systematically in the temperature range from 100 K to 500 K. The green and red UC emissions are sensitive to the sample temperature whereas the excitation power density in the studied temperature ranges plays a negligible role on the red to green UC emissions ratio. The non-contact optical temperature sensing behaviors were investigated based on the fluorescence intensity ratio (FIR) of red (R3 + R4) and green (G3) at temperature from 100 K to 500 K, which are ascribed to non-thermally coupled levels of Ho 3+ : 5 F 5 and 5 F 4 , respectively. The maximum absolute sensitivity (S a ) of 0.0477 K −1 and maximum relative sensitivity (S r ) of 0.0129 K −1 at the temperature range of 100–500 K based on FIR of (R3 + R4)/G3 were found. The mechanism of temperature effect on UC emission was discussed. The heating and cooling cycle test indicates the high thermal stability of LiYF 4 :20Yb 3+ , 1Ho 3+ . These results imply the LiYF 4 :20Yb, 1Ho has potential application in ratiometric thermometers and temperature sensing devices.
Weichang Li,Jixi Xu,Qiang He,Yan Sun,Shiyu Sun,Wei Chen,Malgorzata Guzik,Georges Boulon,Lili Hu
The development of novel phosphors with stable and efficient green and red up-conversion (UC) emission is important for many applications such as fluorescent labeling , color display and anticounterfeiting. In this work, we report a stable and efficient green and red up-converter of LiYF 4 :Yb 3+ ,Ho 3+ octahedrons obtained by modified hydrothermal method . The UC emission and luminescence decays of LiYF 4 :Yb 3+ ,Ho 3+ with various Yb 3+ and Ho 3+ ion concentrations were studied systematically under 976 nm LD excitation. The Yb 3+ and Ho 3+ ion concentrations were optimized to be 20 mol% and 1 mol% respectively, for efficient green and red UC emissions. LiYF 4 :Yb 3+ ,Ho 3+ presents not only controlled morphology of monodisperse octahedrons with length of ∼20 μm and width of ∼10 μm, but also performs efficient green and red UC emissions, which is about four times stronger than that of β-NaGdF 4 : 20 Yb 3+ ,0.5Ho 3+ (NaGdF 4 : 20 Yb 3+ ,0.5Ho 3+ ). More importantly, the stable UC emission with variation of green intensity ratio ΔG% (G% = I 520-570nm /I 500-700nm , ΔG%= (G%) max -(G%) min ) and red intensity ratio ΔR% (R% = I 625-685nm /I 500-700nm , ΔR%= (R%) max -(R%) min ) < 1% was found over 976 nm LD excitation power density (PD) ranging from 1.0 to 5.6 W/cm 2 . Whereas, their variations of ∼6% and 25% are observed at the same excitation PD for NaGdF 4 :20 Yb 3+ ,0.5Ho 3+ and commercial β-NaYF 4 :20 Yb 3+ ,2Er 3+ (NaYF 4 : 20 Yb 3+ ,2Er 3+ ), respectively. The mechanism of green and red UC emissions in LiYF 4 : Yb 3+ ,Ho 3+ as a consequence of energy transfer processes has been briefly discussed taking into account the UC emission kinetics. The highly stable intensity ratio of G% and R% combined with the efficient green UC color hints the potential application of LiYF 4 : Yb 3+ ,Ho 3+ in fluorescent labeling and color display.
危险品化学品经营许可证（带存储）