Quantum cutting abilities of sol-gel derived LiGdF4:Eu3+ powders

Optical properties of europium doped LiGdF4 (LGF) powders synthesized by the sol-gel process were investigated in the VUV range. Emission of two visible photons (due to 5D0→7FJ transitions on two Eu3+ ions) per absorbed VUV photon was demonstrated indicating that a quantum cutting phenomenon takes place. This mechanism is explained by a two-step energy transfer when exciting Gd3+ ions in their 6GJ high energy level. Best luminescence efficiency was recorded at room temperature for samples with a doping rate of 5 mol% in europium ions. Effect of rare-earth concentration on internal quantum cutting efficiency was studied. Temperature dependence was also investigated and showed that the down-conversion process upon excitation at 202 nm becomes inefficient at low temperature since energy transfer from Gd3+ ions to Eu3+ ions is not effective any more. Such a result was connected with the thermal population at room temperature of Eu3+7F1 state which is involves in the first step of the energy transfer.