Energy Transfer Between Activators at Different Crystallographic Sites

Several divalent europium-doped alkali-earth silicon oxide or nitride (AESON) phosphors, which are of great use in white light-emitting diodes, exhibit a two-peak emission. We examined the two-peak emission of Sr2SiO4:Eu2+, which is known as a representative AESON phosphor. The two-peak emission is closely associated with the energy transfer between two different Eu2+ sites. The two-peak emission in light-emitting diode phosphors is a very important issue from a practical point of view because it directly relates to the control of color tuning. By analyzing the time-resolved photoluminescence spectra, we identified the energy transfer taking place between Eu2+ activators located at two different crystallographic sites in the Sr2SiO4 structure. A rate-equation model involving various energy-transfer routes among inhomogeneously distributed activators in the crystalline host was developed and used to give relevant interpretation to color chromaticity.