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Developing a highly reliable non-contact optical thermometer probe with excellent sensitivity and multi-mode temperature sensing behaviours is always a great challenge. Here, dual-emitting luminescent composites fabricated using a europium-based metal–organic framework (Eu-MOF) and surface-immobilized molecular dye (Coumarin 7) were successfully prepared by a simple solvothermal method, followed by a post-modification strategy. Benefiting from the linear response in fluorescence intensity ratios (FIRs) of Eu3+ to Coumarin 7 dye molecules in the temperature range from 10 °C to 90 °C, the composite demonstrated the maximum relative temperature sensitivity (Sr) of 0.50% °C−1 at 90 °C. Moreover, the observed red-shift of Coumarin 7 emission with the temperature readout suggests a dual-mode optical thermal sensing mechanism in the dye-immobilized MOF composite. Their excellent reusability and temperature sensing mechanisms have been also investigated. These results demonstrate the potential of the Coumarin 7 functionalized Eu-MOF composite as a dual-mode optical thermometer for temperature sensing applications.

Template-controlled syntheses via metal–organic frameworks (MOFs) have emerged as a general strategy to fabricate metal oxides with tailored porous structures. Here, novel hierarchical SnO2/α-Fe2O3 hollow microcubes have been obtained by post-loading of Sn2+ ions on the surface of Fe4(Fe(CN)6)3 microcubes and a subsequent thermolysis route. The as-formed hierarchical SnO2/α-Fe2O3 composites exhibit remarkable selective acetone-sensing properties, in which the optimum composition of SnO2/α-Fe2O3 with Sn : Fe = 1.5 exhibits the best response towards 200 ppm acetone gas under the operating temperature of 270 °C (with gas response Ra/Rg = 9.3), with a fast response/recovery speed (6 s/7 s), as well as excellent reproducibility for at least 15 days without a significant change in response. The applied strategy provides a general and controllable method to access other hierarchically structured multi-metal oxide architectures with intriguing morphologies and adjustable sensing properties.

Dual-emitting hierarchical Bi4(GeO4)3/Zn2GeO4 hybrid microspheres have been prepared by a facile one-pot hydrothermal synthesis of Zn2GeO4 with the addition of pre-synthesized BiOBr nanoplates. The phase composition and morphology evolution of the Bi4(GeO4)3/Zn2GeO4 composites are investigated depending on the amounts of BiOBr precursor used in the hydrothermal process. The photoluminescence peaks at 412 and 532 nm for the as-prepared Bi4(GeO4)3/Zn2GeO4 are ascribed to Bi3+ emission and defect-related centers in the Zn2GeO4 component, respectively, and the features show a quenching response toward a temperature increase. The fluorescence intensity ratio (FIR) of Bi3+: 3P1–1S0 (412 nm) to the defect emission center of Zn2GeO4 (532 nm) can be exploited as a self-calibrated temperature index for potential thermometer applications. The maximum relative sensitivity (Sr) is 3.96% °C−1 in the temperature range of 20 °C to 100 °C. This work expands the rational design strategy for controllable particle morphology and structure modulation, and further explores their synergetic distinctive properties and potential optical sensor applications.