Characteristics of down conversion green emitting Ba_3Bi_2(PO_4)_4:Tb~(3+) nanosized particles for advanced illuminating devices

摘要

Nano-scaled green-emitting Ba_3Bi_2(PO_4)4:Tb~(3+) crystalline series was effectively obtained via very efficient and straightforward combustion-synthesis route for the very first time. The JCPDS data (Card No: 780204) of Ba_3Bi_2(PO_4)_4 crystal were used for profiling the diffraction patterns of various mol% samples. The structure and lattice parameters of Ba_3Bi_(1.70)Tb_(0.30)(PO_4)_4 system have been investigated by Rietveld refinement analysis. Further, it was found that incorporation of dopant (Tb~(3+)) ion into the monoclinic crystal lattice of C12/c1 (15) space group symmetry did not induce any major structural changes. Lowering in the optical band-gap value from 4.16 to 4.02 eV was observed when Ba_3Bi_2(PO_4)_4 host lattice is doped with 15 mol% of activator ions. The photoluminescence analysis of Ba_3Bi_2(PO_4)_4:Tb~(3+) series at 368 nm excitation yielded the bright green emission due to the ~5D_4→~7F_5 transition. A maximum in emission intensity is observed corresponding to the Ba_3Bi_(1.70)Tb_(0.30)(PO_4)_4 composition. Critical energy distance (13.235 A) proposed the existence of energy transfer through multipolar interaction (dipole-dipole) phenomenon, which is cross-verified by Huang analysis (s = 4.94). The value of radiative-lifetime and non-radiative transition rate are calculated to be 2.22 ms and 10.3 s~(-1), respectively. Furthermore, the very high value of quantum efficiency (97%) and the results of various optical analysis favor the practical utility of down-conversion Ba_3Bi_(1.70)Tb_(0.30)(PO_4)_4 nanophosphor for solid-state and other illuminating devices.