Thermal quenching of photoluminescence represents a significant obstacle to practical applications such as lighting, display, and photovoltaics. Herein, a novel strategy is established to enhance upconversion luminescence at elevated temperatures based on the use of negative thermal expansion host materials. Lanthanide‐doped orthorhombic Yb2W3O12 crystals are synthesized and characterized by in situ X‐ray diffraction and photoluminescence spectroscopy. The thermally induced contraction and distortion of the host lattice is demonstrated to enhance the collection of excitation energy by activator ions. When the temperature is increased from 303 to 573 K, a 29‐fold enhancement of green upconversion luminescence in Er3+ activators is achieved. Moreover, the temperature dependence of the upconversion luminescence is reversible. The thermally enhanced upconversion is developed as a sensitive ratiometric thermometer by referring to a thermally quenched upconversion.

We report the intense multiphoton upconversion of β-NaYF4: Yb3+–Tm3+ individual nanocrystals benefiting from the perfect ladder-type electron configuration under saturation excitation.

applications. For example, mixed LnMOFs with a dual emission can be constructed by introducing two types of luminescent lanthanide ions into the frameworks. The temperature-sensitive intensity ratio of the dual emission provides self-referencing thermometry, which is immune to fluctuations in the excitation source and in the detection system. By controlling the concentration ratio of lanthanide components in the framework, the performance of the ratiometric thermometer can be readily adjusted. [1] LnMOF thermometers in previous reports were mainly prepared in the form of dispersed particles and intended for probing local temperatures. In order to enable mapping of temperature distribution over a large surface, efforts have been devoted to the synthesis of LnMOF films by depositing preformed LnMOF particles on various substrates. [2][3][4] For example, Cao and co-workers fabricated Ln@UiO-66 hybrid film on fluorinedoped tin oxide (FTO) glass by an electrophoretic deposition method, in which a CH 2 Cl 2 dispersion of MOF powders was placed in an electrode tank and treated under a DC voltage of 9 V for 5 min. [4] In an attempt to develop fast synthesis of LnMOF films, Bouwman and co-workers explored direct growth of mixed Gd/Tb MOF films on a Gd 2 O 3 substrate. The Gd 2 O 3 substrate was prepared by compressing Gd 2 O 3 powder at an ultrahigh temperature (1500 °C) to enhance the mechanical strength. The Gd 3+ ions act as nucleation sites for the growth of the MOF film by a hydrothermal synthesis method. [5] The preparation of Gd 2 O 3 substrate is complicated and the growth of film is at high pressure and temperature condition, which induces high cost in large-scale production. Thus, facile and scalable synthesis of large LnMOF films with a high thermal sensitivity remains an unfulfilled research.In this study, we report a one-step wet chemical synthesis for direct growth of mixed Tb/Eu-BTC MOF films on large quartz substrates (4 cm × 4 cm). Thermometric properties of the LnMOF films are investigated in the 298-383 K range. The thermal sensitivity of the LnMOF films as a function of lanthanide composition was investigated and correlated with the intramolecular energy transfer process. We also demonstrate real-time colorimetric thermal mapping using the Tb/Eu-BTC MOF film.LnMOF composed of 1,3,5-benzenetricarboxylate (H 3 BTC) and lanthanide ions was first reported by Yaghi and co-workers [6] Mixed lanthanide metal-organic framework (LnMOF) films are directly grown on a quartz substrate through a wet chemical synthesis. Thermometric properties of the LnMOF films originating from temperature dependent emission intensity ratio of Tb/Eu are systematically investigated in the 298-383 K range. At an optimized Tb/Eu concentration ratio of 98.0:2.0, the ratiometric thermometer registers a high relative sensitivity of 16.14% K −1 at 359 K. As the temperature increases from 298 to 383 K, the LnMOF film thermometer also displays a distinct change in emission color from green to red, corresponding to a shift in Commission Inte...

Thermal quenching of photoluminescence represents a significant obstacle to practical applications such as lighting, display, and photovoltaics. Herein, a novel strategy is established to enhance upconversion luminescence at elevated temperatures based on the use of negative thermal expansion host materials. Lanthanide‐doped orthorhombic Yb2W3O12 crystals are synthesized and characterized by in situ X‐ray diffraction and photoluminescence spectroscopy. The thermally induced contraction and distortion of the host lattice is demonstrated to enhance the collection of excitation energy by activator ions. When the temperature is increased from 303 to 573 K, a 29‐fold enhancement of green upconversion luminescence in Er3+ activators is achieved. Moreover, the temperature dependence of the upconversion luminescence is reversible. The thermally enhanced upconversion is developed as a sensitive ratiometric thermometer by referring to a thermally quenched upconversion.