Tuneable Red and Blue Emission of Bi-Co-Doped SrF:Eu Nanophosphors for LEDs in Agricultural Applications.

Tunable blue/red dual-emitting Eu-doped, Bi-sensitized SrF phosphors were synthesized utilizing a solvothermal-microwave method. All phosphors have cubic structure (- (225) space group) and well-distinct sphere-like particles with a size of ~20 nm, as examined by X-ray diffraction and transmission electron microscopy. The diffuse reflectance spectra reveal a redshift of the absorption band in the UV region as the Bi concentration in SrF: Eu phosphor increases. Under the 265 nm excitation, photoluminescence spectra show emission at around 400 nm from the host matrix and characteristic orange D → F and deep red D → F Eu emissions. The red emission intensity increases with an increase in Bi concentration up to 20 mol%, after which it decreases. The integrated intensity of Eu red emission in the representative 20 mol% Bi co-doped SrF:10 mol% Eu shows twice as bright emission compared to the Bi-free sample. To demonstrate the potential application in LEDs for artificial light-based plant factories, the powder with the highest emission intensity, SrF: 10Eu, 20 Bi, was mixed with a ceramic binder and placed on top of a 275 nm UVC LED chip, showing pinkish violet light corresponding to blue (409 nm) and red (592, 614, and 700 nm) phosphors' emission.