Role of the Rigid Host Structure in Narrow-Band Green Emission ofEu(2+)in Rb2Na2(Li3SiO4)(4): Insights into Electron-Phonon Coupling

Eu2+-activated alkali-lithosilicate phosphors exhibit narrow-band emis-sions that are attractive to high color-rendition and wide color-gamut displays. Themicroscopic mechanism behind the small emission bandwidth is not presentlyunderstood. Here, we report an explicit calculation of the vibronic process occurringin the narrow-band green emission of Rb2Na2[Li3SiO4]4:Eu2+. We show that due to thehigh rigidity of the host material, the structural strain induced by the localized Eu2+4f-5d excitation is distributed among the atoms far beyond thefirst coordination shell andhence reduces the local structural relaxation around Eu2+. The emission bandshape isthus mainly controlled by the coupling of the electronic transition with the phononmodes associated with motions of host constituent atoms, which was further validatedby the good agreement of the calculated bandshape with the experiment. The resultsprovide insights into the generation of narrow-band emission and improve ourknowledge on electron-phonon coupling of 4f-5d transitions in phosphors