Review—Mn <sup>4+</sup> vs Cr <sup>3+</sup> : A Comparative Study as Activator Ions in Red and Deep Red-Emitting Phosphors
Sadao Adachi
Abstract
The Mn 4+ and Cr 3+ -activated phosphor properties are examined in detail from an aspect of spectroscopic point of view. The phosphor materials discussed here are fluorides and oxides. Such Mn 4+ and Cr 3+ -activated fluoride and oxide phosphors are classified from a different kind of host materials together with the different spectroscopic properties of photoluminescence (PL) and PL excitation (PLE) spectra into five groups: types F-Mn (F = fluoride), F-Cr, O-Mn (O = oxide), O-Cr-A, and O-Cr-B. The spectroscopic properties of the Mn 4+ and Cr 3+ -activated phosphors are examined by analyzing PL and PLE spectra based on the Franck−Condon analysis model. The results show that an energy inequality relation of the zero-phonon line (ZPL) energies for types F-Mn, O-Mn, and O-Cr-A phosphors is given by E ( 2 E g ) ZPL < E ( 4 T 2 g ) ZPL , whereas that for types F-Cr and O-Cr-B phosphors is given by E ( 2 E g ) ZPL ≥ E ( 4 T 2 g ) ZPL . As a result, the former phosphors promise to emit light caused by the 2 E g → 4 A 2 g transitions and the latter ones by the 4 T 2 g → 4 A 2 g transitions. Difference in the temperature-dependent PL intensity between the Mn 4+ and Cr 3+ red and deep red emissions are also discussed in detail.