Lattice Strain Control Luminescence of Phosphors for LEDs

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 M_1.95Eu_0.05Si_5−xAl_xN_8−xO_x 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 Ca₁₂Al_14‑zSi_zO_32+zF_2−z: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.