Photoluminescence Properties of Novel Red-Emitting Mn2+-Activated MZnOS (M = Ca, Ba) Phosphors

Photoluminescence properties of novel red-emitting Mn2+-activated MZnOS (M = Ca, Ba) phosphors were investigated. Mn2+-activated MZnOS phosphors show a single symmetric narrow red emission band in the wavelength range of 550-700 run due to the T-4(1)((4)G) -> (6)A(1)(S-6) transition of Mn2+. Peak centers are at about 614 rim for M = Ca and 634 nm for M = Ba, regardless of the excitation wavelength and Mn2+ doping concentration. A comparison is made between the luminescence properties of Mn2+ in the Ca versus Ba compound. A similarity between them is that both Mn2+-activated CaZnOS and BaZnOS can be efficiently excited under host lattice excitation in the wavelength range of 250-350 nm due to efficient energy transfer between the host lattice (MZnOS) and activator (Mn2+). An unexpected difference is that Mn2+-activated CaZnOS can also be efficiently excited under the excitation of Mn2+ itself (d-d transitions) in the wavelength range of 350-500 nm. This difference is ascribed to different crystal structures, different coordination environments, and point symmetries for Mn in these two compounds. The potential applications of these phosphors are pointed out. Among them, Mn2+-activated CaZnOS shows great potential for application as an alternative red-emitting LED conversion phosphor due to its high absorption and strong excitation bands in the wavelength range of 350-500 nm.