Crystal structure, tunable emission and applications of Ca1−xAl1−xSi1+xN3−xOx:RE (x = 0–0.22, RE = Ce3+, Eu2+) solid solution phosphors for white light-emitting diodes

Abstract

CaAlSiN₃:Eu²⁺ is a very promising red phosphor for high color rendering white light-emitting diodes (wLEDs), but a large part of its emission covers wavelengths longer than 700 nm, which is not detectable by the human eye and thus wasted. Optimizing its luminescence properties will allow us to further enhance the overall optical properties of wLEDs. In this contribution, the luminescence spectra of Ce³⁺ or Eu²⁺-activated CaAlSiN₃ were tuned and tailored by introducing isostructural Si₂N₂O to form solid solutions of Ca_1−xAl_1−xSi_1+xN_3−xO_x (x = 0–0.22). The structural evolutions, microstructure, luminescence, thermal quenching and quantum efficiency of Ca_1−xAl_1−xSi_1+xN_3−xO_x:RE (RE = Ce³⁺, Eu²⁺) were investigated and clarified by using various analytic techniques. Upon introducing Si₂N₂O into CaAlSiN₃, the Ce³⁺-doped CaAl_1−xSi_1+xN_3−xO_x shifted its peak emission from 606 to 575 nm and retained the band width of 145 nm, whereas the Eu²⁺-doped one blue-shifted its emission from 650 to 638 nm and broadened its band width from 90 to 122 nm, owing to the structural distortion and disorder as well as the band gap broadening associated with the solid solution formation. By combining these phosphors with a blue LED, high color rendering (Ra) and luminous efficacy (η) white LEDs were realized (Ra = 82.5 and η = 104 lm W⁻¹ for the Ce³⁺-doped phosphors, and Ra = 97 and η = 101 lm W⁻¹ for the Eu²⁺-doped phosphors).