Ionothermal Synthesis Method

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

Importantly, ionic liquids show excellent properties on the adsorption of microwave. The combination of microwave-assisted synthesis and ionothermal synthesis opens up an efficient and safe route to prepare zeolite materials [60]. Tian and coworkers reported the microwave-assisted ionothermal synthesis of AlPO-ll using [EmimJBr [61]. Silicon element was also successfully introduced to the framework forming SAPO-11 with potential catalytic applications. In addition, Yan and coworkers developed the ambient pressure synthesis method for silicate zeolites by combining the advantages of ionothermal synthesis, dry-gel conversion, and microwave irradiation [62]. With the assistance of microwave-assisted synthesis, the safe and fast process of ionothermal synthesis has shown to be a promising synthetic route for a variety of zeolite structures. 

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