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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]

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]

Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor with respective functions of optical temperature sensing and optical heater are investigated in detail. The Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ film (~200 nm) and powder are successfully prepared, respectively. The crystalline structure is characterized by XRD and the relevant morphologies are analyzed by SEM and AFM, respectively. Based on fluorescence intensity ratio (FIR) technique, photo-thermal behaviors of Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ powder are illustrated. Under 980 nm excitation, the temperature induced by laser is calculated, which varies from 323 to 617 K as exciting power increased from 0.03 to 3.78 W. Additionally, the temperature sensing behaviors of Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ film are investigated. Highly accurate temperature sensing can be realized due to the negligible photo-thermal effect. This thermal sensor exhibited a high sensitivity in the range of 295–660 K, and the maximum value of relative sensitivity was determined as 13.4×10 −3 K −1 at 295 K. These results demonstrate that Gd 2 (MoO 4 ) 3 :Er 3+ /Yb 3+ phosphor can be applied in terms of temperature sensing and optical heater. [ABSTRACT FROM AUTHOR]