Many inorganic phosphors, like those used in white LED lights, contain rare earth compounds with tunable light-emitting properties. However, when a phosphor’s excitation energy band overlaps the emission band, energy can be reabsorbed, changing the spectrum and intensity of the emitted light.

Mingying Peng, South China University of Technology, Guangzhou, and colleagues bypassed this problem by using bismuth as the optically active species. They identified the most promising matrix materials using first-principles calculations of the electronic properties of bismuth in various host environments. They found that YNbO₄, YVO₄, and ScVO₄ could be mixed in various ratios to produce materials with band gaps between 3.63 and 2.58 eV.

Each of these compounds alone produces a characteristic blue photoemission under 265 nm light. Doping the mixed oxides with about 1 % trivalent bismuth extends the photoemission range across the visible spectrum. The full excitation range extends from 340 to 420 nm, and the emission range extends from about 450 nm (blue) to 647 nm (orange-red). The lack of overlap between the emission and excitation spectra solves the problem of emission color purity and visible reabsorption.

• Band-Gap Modulation in Single Bi³⁺-Doped Yttrium–Scandium–Niobium Vanadates for Color Tuning over the Whole Visible Spectrum,
  Fengwen Kang, Haishan Zhang, Lothar Wondraczek, Xiaobao Yang, Yi Zhang, Dang Yuan Lei, Mingying Peng,
  Chem. Mater. 2016.
  DOI: 10.1021/acs.chemmater.6b00277