Metal To Metal Charge Transfer Induced Efficient Yellow/Far‐Red Luminescence in Na2Ca3(Nb, Ta)2O9:Bi3+ toward the Applications of White‐LEDs and Plant Growth Light

TL;DR: In this article , the metal to metal charge transfer (MMCT) in Bi3+doped phosphors is proposed to target the red/far-red luminescence, and the results show that the MMCT state involving the ground state of Bi3 ion and the excited state of host (Nb/Ta)5+ cations in Na2Ca3(Nb, Ta)2O9:Bi3+ induces efficient and tunable yellow/far red luminecence (peaking at 597-667 nm).

Abstract: Red and far‐red spectral components are the basics for color rendering improvement of illumination devices and growth regulation of plants, respectively. Establishing a feasible design principle in solid state materials for the red/far‐red phosphors is significant but challenging. Realizing metal to metal charge transfer (MMCT) in Bi3+‐doped phosphors is a new strategy to target the red/far‐red luminescence. As a proof of concept, the MMCT state involving the ground state of Bi3+ ion and the excited state of host (Nb/Ta)5+ cations in Na2Ca3(Nb, Ta)2O9:Bi3+ induces efficient and tunable yellow/far‐red luminescence (peaking at 597–667 nm). Moreover, benefited from the appropriate distance between Bi3+ and (Nb/Ta)5+ ions, Na2Ca3(Nb, Ta)2O9:Bi3+ possess intense absorption in near‐ultraviolet region and no absorption in visible region. The plant growth light with the blending of Na2Ca3Nb2O9:Bi3+ far‐red phosphor and BAM:Eu2+ blue phosphor yields broadband electroluminescence covering almost the entire absorption spectra of chlorophyll and phytochrome, which is superior to the Cr3+‐ and Mn4+‐based light‐emitting diode (LED) devices. The white‐LED device by employing Na2Ca3Ta2O9:Bi3+ yellow phosphor as the essential component yields full‐spectrum warm white light with high color indexes.