Compositionally Tuned Self-Activated Alkali Metal Vanadates for High Color Rendering White LEDs and IR Reflective Pigments

Abstract

Phosphor-converted white light-emitting diodes (pc-WLEDs) with a supreme color rendering index (CRI) remain challenging, particularly due to the limited accessibility of efficient cyan-green-emitting phosphors in the 480–520 nm emission range. Herein, a novel rare earth-free cyan-green-emitting Ta⁵⁺-substituted CsVO₃ phosphor that exhibits a VO₄^3– charge transfer enabled cyan-green emission band centered at ∼520 nm under the 370 nm near UV (n-UV) light is reported with an internal quantum efficiency of 93.9%. This cyan-green emission profile could align well with the broad-band yellow-orange emission to produce high CRI warm white light. Such yellow-orange emission spectra are achieved by incorporating Cs⁺ ions into the Rb₃V₅O₁₄ system, which tunes the emission color from red to orange and eventually to yellow. Furthermore, the light absorption in Rb_3–xCs_xV₅O₁₄ was followed by internal energy transfer from the 2p O^2– to the 3d V⁵⁺ orbitals, resulting in perceived pigment-type colors ranging from red to yellow with promising NIR reflectance. When combined strategically, they can be excited by n-UV light and generate a well-distributed white light with an impressive CRI of 89 and a low color temperature (CCT) of 4056 K. These findings suggest that the newly developed rare earth-free vanadates hold promise for use in full-spectrum pc-WLEDs.