Photoluminescence and energy transfer behavior of narrow band red light emitting LiBaTb(MoO):Eu.

This work concerns the polycrystalline red emitting solid state compound LiBa(TbEu)(MoO), from which a series of powder samples was prepared by a conventional solid-state reaction. The phase formation of the samples was investigated by X-ray diffraction which revealed the formation of a solid solution without a miscibility gap. Photoluminescence (PL) spectra and decay curves were recorded as a function of Tb and Eu concentration and temperature. It turned out that the external quantum efficiency of Eu photoluminescence is between 30 and 80%, while the highest quantum yield is achieved for about 60% Tb. An increase of emission intensity can be realized by co-doping of Eu and Tb. Moreover, the emission has a luminous efficacy of 275 lm W which is a distinct advantage over the widely applied Mn activated fluorides. The time dependent photoluminescence as a function of Tb concentration demonstrates the presence of an efficient energy transfer from Tb to Eu. Temperature dependent PL measurements revealed that LiBa(TbEu)(MoO) loses just 20% of PL efficiency up to 400 K. Therefore, the investigated phosphors are attractive for application in pcLEDs. It is finally demonstrated that the application of a Eu/Tb co-doped ceramic disc is useful for the colour conversion of a blue emitting LED with a higher conversion rate compared to LiBa(LaEu)(MoO).