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Abstract Owing to few thermal populations or spectral absence at extreme low temperature, fluorescence intensity ratio (FIR) technique based on thermal coupling levels is sometimes unpractical for low temperature sensing. Herein, using bandwidth as a sensing parameter, the low temperature sensing performances of YOF:Yb3+/Tm3+ phosphor are reported. The YOF:10%Yb3+/0.2%Tm3+ phosphor is prepared by hydrothermal and calcined methods. Under 980 nm excitation, the temperature dependent upconversion spectra are recorded in the range of 12–300 K, and the temperature sensing behaviors are investigated in detail. The phosphor exhibits a single-band near-infrared (NIR) luminescence composed of multiple narrow peaks. Thereinto, the ultranarrow bandwidths of 12,485 cm−1 (800.9 nm) and 12,580 cm−1 (794.9 nm) emission bands are only 14 cm−1 (0.9 nm) and 12 cm−1 (0.75 nm) at 12 K, respectively. Based on temperature dependent bandwidth, the maximum relative sensitivities are found to be 0.60% K−1 (12–190 K) and 0.84% K−1 (190–300 K), which enable the YOF:10%Yb3+/0.2%Tm3+ phosphor to be a promising thermometer for low temperature sensing. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

The methods of modulating emitting color are greatly important for up-conversion phosphors to broaden their applications, ranging from information storage to surface display. In this paper, the Ho 3+ /Tm 3+ /Yb 3+ tri-doped Gd 2 (MoO 4 ) 3 phosphors are synthesized by typical sol-gel method. It is found that the phosphors can radiate intense blue (475 nm), green (542 nm) and red (660 nm) up-conversion luminescence under 980 nm or 915 nm laser excitation. Especially, the emission color of the phosphors can be tuned from red to lavender by adjusting the excitation power of 980 nm or 915 nm continuous lasers. In addition, the up-conversion luminescence is also investigated under the excitation of 980 nm pulse laser. The emission color varies from green to blue and green to yellow by altering the pulse width and frequency, respectively. Combining the above methods, multi-color and white light are realized, indicating the potential application in dynamic colorful display. [ABSTRACT FROM AUTHOR]

A strategy to improve the sensitivity of NaLuF 4 :Yb 3+ /Er 3+ is elaborated via incorporation Mn 2+ ions, which results a closed energy transfer between Er 3+ and Mn 2+ ions ( 4 S 3/2 (Er 3+ ) → 4 T 1 (Mn 2+ ) → 4 F 9/2 (Er 3+ )). The NaLuF 4 :Yb 3+ /Er 3+ and NaLuF 4 :Yb 3+ /Er 3+ /Mn 2+ phosphors are prepared by a hydrothermal method. Notably, incorporation Mn 2+ for NaLuF 4 :Yb 3+ /Er 3+ phosphor rusults in enhancing the red to green intensity ratio, which acts as a bridge for energy transfer between 4 S 3/2 and 4 F 9/2 levels of Er 3+ . The temperature sensing behaviors of two phosphors are investigated in the 295–595 K range using a ratiometric technique under 980 nm excitation. Based on thermally ( 2 H 11/2 and 4 S 3/2 ) and non-thermally ( 4 F 9/2 and 4 S 3/2 ) coupled levels of Er 3+ , the influences of this energy transfer are discussed in detail. The sensitivity of NaLuF 4 :Yb 3+ /Er 3+ doping with Mn 2+ ions based on non-thermally coupled levels is much higher than that without Mn 2+ ions based on both thermally and non-thermally coupled levels in the 295–525 K range. The maximum sensitivity is 10.99 × 10 −3 K −1 at 295 K for NaLuF 4 :Yb 3+ /Er 3+ /Mn 3+ phosphor. These meaning results indicate that incorporation Mn 2+ ions in NaLuF 4 :Yb 3+ /Er 3+ phosphor is an effective method for enhancing sensitivity in the 295–525 K range. [ABSTRACT FROM AUTHOR]

Most thermometers suffer from thermal quenching resulting in low signal to noise ratio at elevated temperature. To overcome thermal quenching, we fabricated a negative thermal expansion (NTE) thermometer based on Sc 2 Mo 3 O 12 :Nd3+/Yb3+/Er3+ phosphor. Under 808 nm excitation, the upconversion (UC) emissions of Er3+ ions show the thermal enhancement and its 524 nm emission increases 10-fold as the temperature increased from 310 to 670 K. Furthermore, the temperature sensing behaviors are investigated. It is found fluorescence intensity ratio (FIR) of 524–559 nm is linear with temperature over a wide range of 310–790 K. The maximum relative sensitivity is 0.84% K−1 at 310 K. These results indicate such phosphor not only achieves a high sensitivity, but also exhibits excellent performances at high temperature due to its thermal enhancement. [ABSTRACT FROM AUTHOR]