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Fluorescence intensity ratio-based temperature sensing with a self-referencing characteristic is highly demanded for reliable and accurate sensing. Lanthanide ions with thermally coupled levels have been widely used for ratiometric temperature sensing. However, these systems suffer from low relative temperature sensitivity and poor luminescence signal discriminability. Herein, the concept of indirectly thermally coupled levels is introduced and employed to actualize high performance temperature sensing. By means of the temperature-dependent phonon-assisted non-radiative relaxation, the 4I13/2 excited state (with infrared emission) of Er3+ can be indirectly thermally coupled with the 4S3/2 excited state (with visible emission) under 808 nm or 980 nm excitation. This is experimentally realized in specially designed NaErF4:10Yb@NaYF4 nanocrystals, and the corresponding ratiometric nanothermometer shows excellent luminescence thermal sensing performance with a maximum relative sensitivity value up to 3.76% K−1 at 295 K. [ABSTRACT FROM AUTHOR]

Based on the inner filter effect, a luminescent Zn(ii)/Na(i) metal–organic framework (MOF) {[Zn2Na(L)(HL)2(H2O)2][OAc]·2H2O}n (1, H2L = 5-methyl-1,3-benzenedicarboxylic acid) with excellent stability was constructed for the fluorescence detection of Cu2+ ions. MOF 1 holds a 3D cationic framework in which [(OAc)2(H2O)2]n2n− anions are embedded into its 1D channels. Abundant hydrogen-bonding and π–π interactions in the MOF facilitate electron transfer from ligand-to-metal, resulting in a good luminescence peak at 412 nm and an efficient fluorescence quenching of MOF 1 in the presence of Cu2+ ions, due to the inner filter effect. The interactions between the Cu2+ ions and the OAc− anion in the channel endowed the Cu2+ ions with facile access to be adsorbed, and afforded the selective quenching of fluorescence. The MOF particles are well dispersed in water and the Cu2+ ions are pre-concentrated by adsorption, thus facilitating the determination of Cu2+ ions with a detection limit down to 0.65 μM. Our work thus paves a way for developing MOFs as an appealing platform to construct materials for environmental applications. [ABSTRACT FROM AUTHOR]