2:15 PM - 2:30 PM
▲ [16p-2B-3] Concentration dependency of Eu2+ doped La2.5Ca1.5Si12O4.5N16.5 and the energy levels of the lanthanide ions
Keywords:luminescence
In order to find new silicon nitride based phosphors, a single-particle-diagnosis approach has been developed in our group. One of the phosphors found via this method is Eu2+ doped La2.5Ca1.5Si12O4.5N16.5. It has a strong 5d-4f emission band in the 450 to 650 nm range after excitation with UV or blue light, making it an interesting phosphor for LED applications. For this research, lanthanide doped La2.5Ca1.5Si12O4.5N16.5 powders have been prepared via a solid-state reaction synthesis. An unusually large shift to longer wavelengths of the position of the emission band was observed for the Eu doped phosphors with increasing Eu concentration. The shift has been attributed to a change in distribution of the Eu ions over the two different crystallographic sites, and energy transfer between these sites. The effect of Eu concentration on the distribution and energy transfer, and with it the effects on the luminescence properties, have been investigated in detail by analyzing the luminescence decay time and temperature dependency of the luminescence as a function of the Eu concentration. Doping with Ce3+ also gave rise to 4f-5d absorption bands, that resulted in blue 5d-4f emission after excitation with UV light. The optical properties of the Ce doped phosphors were compared with those of the Eu doped phosphors, and used to construct an energy level scheme, showing the energy level positions of all lanthanides in La2.5Ca1.5Si12O4.5N16.5 relative to the valence and conduction band. The scheme could be used to explain the absorption and emission spectra of samples doped with samarium and ytterbium, as well as the luminescence thermal quenching behavior of the Ce and Eu doped phosphors.