Synthesis and optical properties of green emitting garnet phosphors for phosphor-converted light emitting diodes

A series of Ce3+ doped CaLu2Al4SiO12 garnet phosphors was prepared by a sol–gel combustion technique. All samples were characterized by powder X-ray diffraction (XRD), thermal quenching (TQ), fluorescence lifetime and photoluminescence (PL) measurements. Moreover, luminous efficacies (LE), CIE 1931 color points and quantum efficiencies (QE) were determined and discussed. XRD patterns confirmed the presence of single phase garnet for all samples independent of Ce3+ concentration at least up to 3 mol%. Phosphors showed a broad band emission in the range 460–720 nm. The emission band maximum is blue-shifted in comparison to Lu3Al5O12:Ce3+ and shifts from 520 to 542 nm by increasing the Ce3+ concentration. High quantum efficiencies of 80 to 86% were obtained for those samples doped with 0.25% and 0.5% of Ce3+, however, a higher Ce3+ doping levels resulted in concentration quenching, i.e. in a substantial decrease of the photoluminescence quantum efficiency.

► Incorporation of Ca2+–Si4+ pair into garnets leads to blue shift of Ce3+ emission.
► Stronger thermal quenching is observed for samples with higher Ce3+ concentration.
► Quantum efficiency decreases if Ce3+ concentration is increased.