Dependence on charge transfer band and emission properties by the crystal chemistry of A- and B-site cations in Eu~(3+)-doped quaternary pyrochlore-type red phosphors Ca(RE)_(1-x)(M)NbO_7 (RE = Y, Gd; M = Ti, Sn)

摘要

Dependence on charge transfer (CT) band and emission properties are investigated in Eu~(3+) doped quaternary pyrochlore-type oxides,Ca(RE)_(1-x)(M)NbO_7 (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 Eu~(3+) in CaYTiNbO_7 resulting in improved Eu~(3+) excitation levels. Contrary to this, the CT band is positioned at a lower wavelength and intense in highly polarizable environment of Eu~(3+) in CaGdSnNbO_7 leading to poor energy transfer to Eu~(3+) excitation levels. Consequently, CaY_(0.85-) TiNbO_7:0.15Eu~(3+) exhibited intense narrow red emission (fwhm3.4 nm) with high asymmetric ratio 8. Further, the phosphors CaY_(0.85)TiNbO_7:0.15Eu~(3+) 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 Y_2O_3:Eu~(3+) red phosphor. Thus, these phosphors are potential candidates for pc-WLEDs applications.