The yttrium organic framework (Y 0.89 Tb 0.10 Eu 0.01 ) 6 (BDC) 7 (OH) 4 (H 2 O) 4 (BDC = benzene-1,4-dicarboxylate) is hydrothermally stable up to at least 513 K and thermally stable in air in excess of 673 K. The relative intensities of luminescence of Tb 3 + and Eu 3 + are governed by Tb 3 + -to-Eu 3 + phonon-assisted energy transfer and Tb 3 + -toligand back transfer and are responsible for the differing temperature-dependent luminescence of the two ions. This provides a ratiometric luminescent thermometer in the 288-573 K temperature range, not previously seen for MOF materials, with a high sensitivity, 1.69 � 0.04 % K À 1 at 523 K. In aqueous conditions, loosely bound H 2 O can be replaced by D 2 O in the same material, which modifies decay lifetimes to yield a quantitative luminescent D 2 O sensor with a useful sensitivity for practical application.