Quantum efficiency of down-conversion phosphor LiGdF4 : Eu

The optical properties of the down-conversion phosphor LiGdF4 : Eu (LGF) were studied. Based on excitation and emission spectra, the down-conversion efficiency was confirmed to be 195%. However, only quantum cutting was observed by direct excitation into the 6GJ states of Gd3+. For the first time, the external quantum efficiency of LGF was determined. For this purpose two independent methods were applied. On the one hand, the quantum efficiency was determined by quantitative comparison of the emission spectra of LiGdF4 : Eu and Y2O3 : Eu. In addition, the quantum efficiency of LiGdF4 : Eu was determined based on reflection spectra. Both methods yielded 32% quantum efficiency while exciting the 6GJ states of Gd3+, including the effect of quantum cutting.