Yellow-Orange-Emitting CaAlSiN3:Ce3+ Phosphor: Structure, Photoluminescence, and Application in White LEDs

Abstract

The crystal structure and photoluminescence properties of undoped and Ce 3+ -doped CaAlSiN 3 as well as the application of white-light LEDs are reported. CaAlSiN 3 and CaAlSiN 3:Ce 3+ have been synthesized, starting from Ca 3 N 2, AlN, Si 3 N 4, and CeN or CeO 2 with and without Li 3 N, by a solid state reaction at 1700 °C for 4 h under high purity nitrogen atmosphere. Instead of an ideal CaAlSiN 3, a more appropriate formula is proposed to be CaAl 1−4δ/3 Si 1+δ N 3 (δ ≈ 0.3−0.4) with an Al/Si ratio of about 1:2 on the basis of the bond valence sum calculations, in which Al/Si is disorderly occupied on the 8b site within Cmc 2 1 space group. Ce 3+ can be incorporated into the host lattice of CaAlSiN 3, and the estimated maximum solubility of Ce 3+ is about x = 0.02 (e.g., 2.0 mol % with respect to Ca) of Ca 1−2 x Ce x Li x AlSiN 3 . CaAlSiN 3:Ce 3+ can be efficiently excited by blue light (450−480 nm) and yields yellow-orange emission with a broadband peaking in the range of 570−603 nm, originating from the 5d 1 → 4f 1 transition of Ce 3+ . With an increase of Ce concentration, the emission band of Ce 3+ shifts to longer wavelengths due to the increased Stokes shift corresponding to structural relaxation and energy transfer of Ce 3+ . Upon excitation in blue light range (450−480 nm), the absorption and external quantum efficiency are about 70% and 56%, respectively, for both Ca 1−2 x Ce x Li x AlSiN 3 and Ca 1− x Ce x AlSiN 3−2 x /3 O 3 x /2 at x = 0.01. In addition, Ca 1−2 x Ce x Li x AlSiN 3 and Ca 1− x Ce x AlSiN 3−2 x /3 O 3 x /2 show high thermal stability in air with the quenching temperature above 300 °C for x = 0.01. Using single CaAlSiN 3:Ce 3+ as the wavelength conversion phosphor combined with a blue InGaN LED-chip (450 nm), warm white-light LEDs can be generated, yielding the luminous efficacy of about 50 lm/W at color temperature 3722 K and the color rendering index (Ra) of 70, which demonstrates that CaAlSiN 3:Ce 3+ is a highly promising yellow-orange phosphor for use in white-light LEDs.