A remarkably tunable emission from red to yellow to green in Mn4+-activated CaAl12O19 phosphor via co-doping Bi3+

Abstract

In this study, Bi3+ and Mn4+ co-doped CaAl12O19 phosphors were prepared via high-temperature solid-state reaction method, and their crystal structure, particle morphologies, luminescence properties, charge compensation mechanism and crystal field effect were investigated in detail. A most remarkable tuning effect can be achieved when the Bi3+ concentration is 5% in CaAl12O19:Bi3+, 0.05% Mn4+ and the electric multipolar interaction is inferred to be the main mechanism for concentration quenching effect. It is also found that, as charge compensators rather than sensitizers, Bi3+ ions can effectively tailor the emissions in a wide range through partial reducing Mn4+ to Mn2+. The charge compensation physics presumably involves the shift of Fermi energy level (EF) and variations of valence states of manganese ions after Bi3+ introduction. Moreover, the authors calculated the splitting energy (Δ) and Racah parameters (B and C) for Mn4+ in octahedral sites and Mn2+ in tetrahedral sites by combining excitation spectra with Tanabe-Sugano diagram. The experimental results will be of certain helpfulness in developing phosphors used in white LED.