Dependence on charge transfer band and emission properties by the crystal chemistry of A- and B-site cations in Eu3+-doped quaternary pyrochlore-type red phosphors Ca(RE)1−x(M)NbO7 (RE = Y, Gd; M = Ti, Sn)

Abstract

Dependence on charge transfer (CT) band and emission properties are investigated in Eu3+ doped quaternary pyrochlore-type oxides,Ca(RE)1−x(M)NbO7 (RE = Y, Gd; M = Ti, Sn) by varying the crystal chemistry of A- and B-cations. The CT band is shallow and extending to higher wavelength in highly covalent environment of Eu3+ in CaYTiNbO7 resulting in improved Eu3+ excitation levels. Contrary to this, the CT band is positioned at a lower wavelength and intense in highly polarizable environment of Eu3+ in CaGdSnNbO7 leading to poor energy transfer to Eu3+ excitation levels. Consequently, CaY0.85TiNbO7:0.15Eu3+ exhibited intense narrow red emission (fwhm3.4 nm) with high asymmetric ratio 8. Further, the phosphors CaY0.85TiNbO7:0.15Eu3+ prepared through citrate-gel route show high quantum efficiency (74%) and sharper red emission (fwhm3.2 nm) with intensity values 8 times better than the solid state one and comparable to the commercial Y2O3:Eu3+ red phosphor. Thus, these phosphors are potential candidates for pc-WLEDs applications.