Broad greenish-yellow luminescence in CaMoO4 by Si4+ acceptor doping as potential phosphors for white light emitting diode applications

Intense broad greenish-yellow luminescence has been observed in CaMoO4 by Si4+ acceptor doping. The broad intense luminescence is attributed to the increased charge transfer transitions in MoO4 (2-) groups and defect luminescence due to distortion and defects. The Si4+ doping acts on two fronts, distorting the MoO4 tetrahedron and inducing oxygen vacancies promoting acceptor levels near the VB edge. The XPS core level spectra analysis indicates an asymmetric broadening of the peaks with an increase of fwhm suggesting defects and oxygen vacancies in the system. The defect and charge transfer luminescence increases competitively with Si4+ doping. The lifetime of the defect luminescence increases with Si4+ doping which suggests the increased radiative emissive transitions without quenching. These factors broadened the luminescence covering the most visible region (425-625 nm) enhancing the fwhm. The calculated CIE chromaticity coordinates fall in the greenish-yellow region with values (0.31, 0.45) making them potential phosphors for white LED applications.