FULL PAPER © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 wileyonlinelibrary.com of this technique, the discovery of new materials with tuneable luminescence is very important and has recently become an active research area. Among phos- phors, such as organic dyes, [3] polymers, [4] semiconductor nanocrystals, [5] lanthanide (Ln)-based materials are the most versa- tile thermal probes used in luminescent nanothermometers. [6] Several examples of such materials demonstrating their application in sensing or mapping at the submicrometer scale were reported: Er 3+ / Yb 3+ co-doped fluoride glass [7] or PbF 2 nanoparticles, [8] glued at the extremity of an atomic force microscope scanning tip, NaYF 4 :(Er 3+ ,Yb 3+ ) [9] and Ln-doped NaGdF 4 core–shell nanoparticles; [10] Y 2 O 3 :Eu 3+ , [11] Y 3 Al 5 O 12 :Ce 3+ , [12] and Mo sensitized rare- earth oxide nanoparticles; [13] and siloxane-based nanoparticles incorporating a Eu 3+ tris(β-diketonate) complex. [14] The temper- ature determination is usually based on the change of the lumi- nescence intensity or decay times. However, the measurements based on a single f–f transition may be much affected by the variation of the sensor concentration and the drift of the optoe- lectronic systems, namely, the excitation sources and detectors. Recently, Carlos and co-workers, reported self-reference nano- thermometers based on the intensity ratio of two f–f transitions that overcome the drawbacks of temperature determination with a single transition. [6a,15] Metal–organic frameworks (MOFs) are crystalline mate- rials consisting of well-defined networks formed by the self- assembly of metal cations and organic linkers. The lumines- cence properties of MOFs have attracted attention due to the unique hybrid networks of these materials, in which both the inorganic and organic moieties may be optically active, ena- bling a wide range of emissive phenomena found in few other classes of materials. [16] Moreover, the occurrence of distinctive processes, such as metal–ligand charge-transfer and host– guest interactions [16a] along with the ease of modification (e.g., doping in composition [17] ) provide a wealth of opportunities for engineering luminescence properties. In the past two decades, luminescent MOFs have found potential applications in chem- ical sensing, light-emitting devices, and biomedicine. [16,18] The use of luminescent MOF nanoparticles in sensing, biomedical imaging, and drug delivery is also well documented. [19] Cui et al. reported the first ratiometric luminescent MOF thermometer, Eu 0.0069 Tb 0.9931 –DMBDC (DMBDC = 2,5-dimethoxy-1,4-ben- zenedicarboxylate), based on the emissions of Tb 3+ at 545 nm and Eu 3+ at 613 nm. [20] Recently, the same group suggested a Lanthanide–Organic Framework Nanothermometers Prepared by Spray-Drying Zhuopeng Wang, Duarte Ananias, Arnau Carné-Sánchez, Carlos D. S. Brites, Inhar Imaz, Daniel Maspoch, João Rocha,* and Luís D. Carlos* Accurate, noninvasive, and self-referenced temperature measurements at the sub- micrometer scale are of great interest, prompted by the ever-growing demands in the fields of nanotechnology and nanomedicine. The thermal dependence of the phosphor's luminescence provides high detection sensitivity and spatial resolu- tion with short acquisition times in, e.g., biological fluids, strong electromagnetic fields, and fast-moving objects. Here, it is shown that nanoparticles of [(Tb 0.914 Eu 0.086 ) 2 (PDA) 3 (H 2 O)]·2H 2 O (PDA = 1,4-phenylenediacetic acid), the first lan- thanide–organic framework prepared by the spray-drying method, are excellent nanothermometers operating in the solid state in the 10–325 K range (quantum yield of 0.25 at 370 nm, at room temperature). Intriguingly, this system is the most sensitive cryogenic nanothermometer reported so far, combining high sensitivity (up to 5.96 ± 0.04% K -1 at 25 K), reproducibility (in excess of 99%), and low-temperature uncertainty (0.02 K at 25 K). DOI: 10.1002/adfm.201500518 Dr. Z. Wang, Dr. D. Ananias, Dr. C. D. S. Brites Prof. J. Rocha, Prof. L. D. Carlos Departments of Chemistry and Physics, CICECO University of Aveiro 3810-193 Aveiro, Portugal E-mail: rocha@ua.pt; lcarlos@ua.pt Dr. A. Carné-Sánchez, Dr. I. Imaz, Prof. D. Maspoch ICN2 (ICN-CSIC) Institut Catala de Nanociencia i Nanotecnologia Esfera UAB 08193 Bellaterra, Spain Prof. D. Maspoch Institució Catalana de Recerca i Estudis Avançats (ICREA) 08100 Barcelona, Spain 1. Introduction Precise temperature measurement at the submicrometer scale is an important challenge encountered, namely, in the fields of nanotechnology and nanomedicine. [1] Thermometers working in an accurate, noninvasive way and with a high spa- tial resolution are critical to monitoring numerous processes at the microscale and nanoscale within electronic and pho- tonic devices, such as thermal transport, heat dissipation, and thermal reactions. [2] As a recently emerged noninvasive tech- nique, the thermal dependence of the phosphor's luminescence provides a high detection sensitivity and spatial resolution, with short acquisition times, in biological fluids, strong elec- tromagnetic fields, and fast-moving objects, for which the con- ventional methods are ineffective. To fulfill the great potential Adv. Funct. Mater. 2015, DOI: 10.1002/adfm.201500518 www.afm-journal.de www.MaterialsViews.com