Lattice Strain Control Luminescence of Phosphors for LEDs

Wednesday, 8 October 2014: 08:10
Sunrise, 2nd Floor, Star Ballroom 4 & 5 (Moon Palace Resort)
R. S. Liu (Department of Chemistry, National Taiwan University)
We successfully control luminescence of phosphors such as M2Si5N8:Eu (M = Ca, Sr, Ba) and Ca12Al14O32F2:Eu with lattice strain effects. we show that size-mismatch between host and dopant cations tunes photoluminescence shifts systematically in M1.95Eu0.05Si5−xAlxN8−xOx lattices, leading to a red shift when the M = Ba and Sr host cations are larger than the Eu2+ dopant, but a blue shift when the M = Ca host is smaller. A local anion clustering mechanism in which Eu2+ gains excess nitride coordination in the M = Ba and Sr structures, but excess oxide in the Ca analogues, is proposed for these mismatch effects (Fig. 1). Furthermore, the Ca12Al14zSizO32+zF2z:Eu revealed a crystal chemistry approach to reduce Eu ions from 3+ to 2+ in the lattice which replacing Al3+−F by the appreciate dopant Si4+−O2 is adopted to enlarge the activator site that enables Eu3+ to be reduced (Fig. 2). Photoluminescence results indicated that as-synthesized phosphors display an intense blue emission peaking at 440 nm that was produced by 4f−5d transition of Eu2+, along with the intrinsic emission of Eu3+ under UV excitation. According to these results, we demonstrate that optical and other properties that are sensitive to local coordination environments.