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 eff iciency was confirmed to be 195%. However, only quantum cutting was observe d by direct excitation into the (6)G(J) states of Gd3+. For the first time, the external quantum efficiency of LGF was determined. For this purpose tw o independent methods were applied. On the one hand, the quantum efficiency was determined by quantitative comparison of the emission spectra of LiGdF 4:Eu and Y2O3:EU. In addition, the quantum efficiency of LiGdF4:Eu was dete rmined based on reflection spectra. Both methods yielded 32% quantum effici ency while exciting the (6)G(J) states of Gd3+, including the effect of qua ntum cutting. (C) 2001 Elsevier Science B.V. All rights reserved.