Metal To Metal Charge Transfer Induced Efficient Yellow/Far‐Red Luminescence in Na<sub>2</sub>Ca<sub>3</sub>(Nb, Ta)<sub>2</sub>O<sub>9</sub>:Bi<sup>3+</sup> toward the Applications of White‐LEDs and Plant Growth Light
Hongzhi Zhang, Jing Zhang, Yuchang Su, Xinmin Zhang
Abstract
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 Bi 3+ ‐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 Bi 3+ ion and the excited state of host (Nb/Ta) 5+ cations in Na 2 Ca 3 (Nb, Ta) 2 O 9 :Bi 3+ induces efficient and tunable yellow/far‐red luminescence (peaking at 597–667 nm). Moreover, benefited from the appropriate distance between Bi 3+ and (Nb/Ta) 5+ ions, Na 2 Ca 3 (Nb, Ta) 2 O 9 :Bi 3+ possess intense absorption in near‐ultraviolet region and no absorption in visible region. The plant growth light with the blending of Na 2 Ca 3 Nb 2 O 9 :Bi 3+ far‐red phosphor and BAM:Eu 2+ blue phosphor yields broadband electroluminescence covering almost the entire absorption spectra of chlorophyll and phytochrome, which is superior to the Cr 3+ ‐ and Mn 4+ ‐based light‐emitting diode (LED) devices. The white‐LED device by employing Na 2 Ca 3 Ta 2 O 9 :Bi 3+ yellow phosphor as the essential component yields full‐spectrum warm white light with high color indexes.