Neighboring-Cation Substitution Tuning of Photoluminescence by Remote-Controlled Activator in Phosphor Lattice

Abstract

Highly efficient red phosphors with superior intrinsic properties that are excited by ultraviolet or blue light-emitting diodes are important white light sources for our daily life. Nitride-based phosphors, such as Sr2Si5N8:Eu(2+) and CaAlSiN3:Eu(2+), are commonly more red-shifted in photoluminescence and have better thermal/chemical stability than oxides. Cation substitutions are usually performed to optimize photoluminescence and thermal quenching behavior. However, the underlying mechanisms are unclear in most cases. Here we show that neighboring-cation substitution systematically controls temperature-dependent photoluminescence behavior in CaAlSiN3:Eu(2+) lattice. Trivalent cation substitution at the Ca(2+) site degrades the photoluminescence in high-temperature environments but achieves better thermal stability when the substituted cation turns monovalent. The neighboring-cation control of lifetime decay is also observed. A remote control effect that guides Eu(2+) activators in selective Ca(2+) sites is proposed for neighboring-cation substitution while the compositional Si(4+)/Al(3+) ratio adjusts to the valence of M(n+) (n = 1-3) cation. In the remote control effect, the Eu(2+) activators are surrounded with nitride anions which neighbor with M(3+)-dominant and Si(4+)/Al(3+)-equivalent coordination when M is trivalent, but shift to the site where surrounded nitride anions neighbor with M(+)-dominant and Si-rich coordination when M is monovalent. This mechanism can efficiently tune optical properties, especially thermal stability, and could be general to luminescent materials, which are sensitive to valence variation in local environments.

Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

“…The K 2 TiF 6 :Mn 4 þ (5.50 at.%) phosphor has an activation energy (E a ) of B0.70 eV, which is 3 times as high as that of nitride compounds (B0.25 eV) 52 . This verifies the excellent thermal stability of K 2 TiF 6 :Mn 4 þ phosphors.…”

Remote Control Effect of Li+, Na+, K+ Ions on the Super Energy Transfer Process in ZnMoO4:Eu3+, Bi3+ Phosphors

“…At present, adjusting the lattice environment of activators is a hotspot for solid state lighting7. In order to improve the luminescence efficiency, site occupation of activators in host lattice has been investigated from different perspectives5789. Peng5 found the site occupancy preference of Mn 4+ in Sr 4 Al 14 O 25 is at the Al(4) and Al(5) higher covalent sites rather than the Al(6) site.…”

Thermal effects in (oxy)nitride phosphors

“…Reaction temperature was then increased and maintained at 1600°C for 2 h with flowing nitrogen gas (99.999% purity). Moreover, this method afforded excellent results in the synthesis of nitridosilicates (Ca 1-x Li x )(Al 1-x Si 1+x )N 3 :Eu [19]. Third, nitridosilicates (MYSi 4 N 7 :Eu 2+ {M = Ca, Sr, Ba}) [20] were synthesized from the stoichiometric mixture of CaCO 3 , SrCO 3 , BaCO 3 , Y 2 O 3 , and Eu 2 O 3 through carbothermal reduction and nitridation.…”