In the last decade, numerous Ln‐bearing metal‐organic frameworks (MOFs) have been reported for luminescence thermometry applications. Although the Ln3+ composition is always thoroughly determined, this parameter is never optimized to improve thermometric performances. Here, the optimization of thermometric performances of luminescent probes is tackled by reporting a series of mixed Eu3+–Tb3+ metal‐organic frameworks. The thermometric performances are accessed as a function of the Eu3+ content yielding a maximum relative sensitivity between 0.19 and 0.44% K−1 registered at temperatures between 340 and 240 K, respectively. A meticulous theoretical investigation of the Tb3+‐to‐Eu3+ energy transfer in the series of mixed Eu3+–Tb3+ MOFs is also performed to determine the predominant pathway of the energy transfer. For the first time, a clear evidence of the significant influence of the Eu/Tb ratio on the energy transfer between Ln3+ emitting centers is presented that definitively determines the operating temperature range and the maximum relative sensitivity of the luminescent thermal probes.

Mesoporous silica monoliths with various ordered nanostructures containing transition metal M(2+) cations in variable amounts were elaborated and studied. A phase diagram depicting the different phases as a function of the M(2+) salt/tetramethyl orthosilicate (TMOS) and surfactant P123/TMOS ratios was established. Thermal treatment resulted in mesoporous monoliths containing isolated, accessible M(2+) species or condensed metal oxides, hydroxides, and salts, depending on the strength of the interactions between the metal species and the ethylene oxide units of P123. The ordered mesoporosity of the monoliths containing accessible M(2+) ions was used as a nanoreactor for the elaboration of various transition metal compounds (Prussian blue analogues, Hofmann compounds, metal-organic frameworks), and this opens the way to the elaboration of a large range of nanoparticles of multifunctional materials.