Novel series of quaternary fluoride nanocrystals: room-temperature synthesis and down-shifting/up-converting multicolor fluorescence

We have developed a straightforward wet-chemical approach for the preparation of pure-phase M2NaScF6 (M = K, Rb, Cs) quaternary fluoride nanocrystals at ambient conditions without high-temperature calcination or sophisticated experimental setups. The production of nanocrystals is highly dependent on the chelating agent, the feed ratio of chelating agent to Sc3+, and the feed ratio of (KOH + NaOH) to Sc3+. Down-shifting and up-converting multicolor fluorescence involving red, blue-white, green, and NIR can be realized by incorporating lanthanide dopants into these host lattices at room temperature. Especially, single-band up-converting and down-shifting dual-modal emissions were achieved. The findings demonstrated that these hexafluoroscandates are versatile hosts for down-shifting and up-converting multicolor fluorescence. This solution-phase procedure is suitable for lab-scale and industrial production of nanocrystals without high-temperature annealing, and can be extended to the fabrication of other polynary rare earth fluorides.