The first example of ratiometric Eu/Tb thermometer based on a lanthanide phosphonate is reported, which presents a temperature dependent emission under 393 nm excitation that enables its use as a molecular thermometer with maximum relative sensitivity of 3.9 %K-1 and minimum temperature uncertainty of 0.15 K, both at 38 K. Additionally, the compound is a competitive luminescent colorimetric probe showing temperature dependent (x,y) CIE color coordinates changing from the yellow, (0.48, 0.48) at 18 K, to the red, (0.64, 0.37) at 300 K.