Recent progress in Eu2+ activated red phosphors for white LEDs and laser displays: focusing on efficient host screening and innovative structural design
Yuhua Wang, Zebin Li, Manrui Xue, Zeyu Lai, Wenlei Cao
Abstract
For white LEDs and LDs displays, Eu 2+ activated red phosphor systems have significant advantages and development potentials over other ion activated systems such as Mn 4+ and Mn 2+ . The variation of the 5d level of Eu 2+ in the matrix is mainly affected by three effects, namely, the nephelauxetic effect (centroid shift ε c ), the crystal field effect (5d level splitting ε cfs ) and the Stokes shift (ΔS). Based on the mechanism of these three effects to achieve red emission, we summarise the Eu 2+ activation of red phosphors with different kinds of substrates. Narrow band emission requires Eu 2+ to be in a highly symmetric ligand structure environment in the lattice. According to this feature, different types of Eu 2+ activated narrow band red phosphors are concluded. Based on quantifiable key performance indicators including excitation/emission wavelengths, full width at half maximum (FWHM), external quantum efficiency (EQE), and luminescence thermal stability, Eu 2+ activated nitride/oxynitride phosphors demonstrate superior overall luminescent performance compared to oxide phosphors in both broadband and narrowband red phosphors. Further research is needed to promote the overall luminescence performance of the Eu 2+ activated nitride/oxynitride and oxide red phosphors for white LEDs and LDs displays as well as to explore the novel efficient red phosphors.