High-gravity-assisted green synthesis of rare-earth doped calcium molybdate colloidal nanophosphors

Abstract

Abstract In this work, we report an innovative route for the synthesis of rare-earth doped calcium molybdate (CaMoO4) nanophosphors by using high gravity rotating packed bed (RPB) technology and paraffin liquid as the solvent. The significant intensified mass transfer and micromixing of reactants in the RPB reactor are benefiting for homogeneous doping of rare-earth ions in the host materials, leading to nanophosphors with high quantum efficiency. The use of liquid paraffin as the solvent eliminates the safety risks associated with volatile organic compounds, increasing the potential for clean production of nanophosphors. Under excitation of deep ultraviolet (DUV) light, the CaMoO4:Na+, Eu3+ nanophosphors exhibit red emission at peak wavelength of 615 nm and quantum yield of up to 35.01%. The CaMoO4:Na+,Tb3+ nanophosphors exhibit green emission at peak wavelength of 543 nm with quantum yield of up to 30.66%. The morphologies of the nanophosphors are tunable from nanofibers through nanorods to nanodots and the possible mechanism of controlling the formation of different nanostructures is proposed on the basis of experimental results and theoretical analysis of mesoscience. These nanophosphors are highly dispersible in organic solvents and utilized for fabricating fabrication of flexible, freestanding luminescent films based on silicone resin. We also demonstrate the red LEDs consisting of the hybrid films of CaMoO4:Na+,Eu3+ nanoparticles as color-converting phosphors and DUV LEDs as illuminators, offering strong potential for future nanophosphors-basedsolid-state lighting systems.