Synthesis and characterizations of YZ-BDC:Eu3+,Tb3+ nanothermometers for luminescence-based temperature sensing.

In the present work, nanothermometers based on amorphous zirconium metal-organic frameworks co-doped with rare-earth ions (YZ-BDC:Eu3+,Tb3+ nanothermometers) with sizes of about 10-30 nm were successfully synthesized via a microwave-assisted hydrothermal method at 120 °C for 15 min. The determined BET surfaces area, total pore volume and average pore diameter were ∼530 m2 g-1, 0.45 cm3 g-1 and 3.4 nm, respectively. Based on Fourier transform infrared spectroscopy (FTIR) and simultaneous thermal analysis (STA) results, the formation process of carboxylic acid salts and the molecular formula of the samples have been proposed. The thermometric properties of Zr-BDC:Eu3+,Tb3+ nanothermometers and their Y3+ ion co-doped counterparts (YZ-BDC:Eu3+,Tb3+) measured in the 133-573 K temperature range were compared. Moreover, the temperature-dependent CIE(x, y) chromaticity coordinates and emission color of the samples were also determined. As the temperature increased from 133 to 573 K, the emission color of Zr-BDC:Eu3+,Tb3+ nanothermometers without the presence of Y3+ ions changed from orange to red, while for YZ-BDC:Eu3+,Tb3+ nanothermometers, the emission color changed from yellow to orange, due to the strong effect of the presence of Y3+ ions on the luminescence intensity of Eu3+ and Tb3+ ions. The maximum relative sensitivity (S Rmax) in both materials was close to 0.5%/K, however, the temperature range of their occurrence was significantly shifted toward higher temperatures due to doping with Y3+ ions. The obtained results showed that doping with Y3+ ions not only enables the modulation of the useful temperature range with high relative sensitivity, but also provides improved thermal stability.