Particle-swarm-optimization-assisted rate equation modeling of the two-peak emission behavior of non-stoichiometric 
CaAl_xSi_(7-3x)/4N_3:Eu^2+ phosphors

Abstract

We examined non-stoichiometric CaAl(x)Si((7-3x)/4)N(3):Eu(2+) phosphors that were intentionally prepared with x = 0.7-1.3 to identify the origin of the deconvoluted Gaussian components that constitute the emission spectra of stoichiometric CaAlSiN(3):Eu(2+) phosphors. The Al/Si molar ratio around the Eu(2+) activator caused the deconvoluted Gaussian peaks. The Eu(2+) activator sites in Al-rich environments gave rise to the lower-energy emission peak, while those in Si-rich environments were related to the higher-energy emission peaks. Active energy transfer from the Eu(2+) activator site in the Si-rich environment to the Eu(2+) activator site in the Al-rich environment was confirmed. Particle swarm optimization was employed to estimate the nine unknown decision parameters that control the energy transfer process. All of the decision parameters were estimated within the range of reasonable values.

Photoluminescent and Structural Properties of MgAlSiN[sub 3]:Eu[sup 2+] Phosphors

“…However, we also observed the same finding in CaAlSiN 3 :Eu 2+ phosphors and have suggested a plausible explanation-the local structure difference gave rise to the different emission peaks, and active energy transfer between them caused the varying decay rates as a function of the detection wavelength. 25,26 This interpretation could be applicable not only to CaAlSiN 3 :Eu 2+ but also to MgAlSiN 3 :Eu 2+ .…”

Linking Macro- and Micro-structural Analysis with Luminescence Control in Oxynitride Phosphors for Light-Emitting Diodes

“…Moreover, the larger the valency is, the more strongly it will pull away from the charge from the activator and the ligand will be. This phenomenon explains why the emission spectrum will redshift when the Si 4+ ions are substituted by Al 3+ ions. − In the current case, the redshift contribution can be attributed to the substitution of Al 3+ ions by Li + ions because Li + possesses lower charges. This effect makes Li + pull less charge away from the ligands and leads to a stronger interaction between the activator and ligands; hence, the stronger nephelauxetic effect can be expected.…”

Effects of Variation in Al Content on the Emission of Eu Doped CaAlSiN3 Red Phosphor Synthesized by Combustion Synthesis Method for White LEDs

“…J. Yang et al reported the Eu 2+ doped CaAlSiN 3 fabricated by an alloy-nitridation method, and the increase of Al/Si molar ratio makes red shift of emission band [ 5 ]. Y. W. Jung reported that the higher Al/Si ratio deactivated the high-energy component and a red-shift was observed [ 6 ].…”