Study on the pathway of performance improvement and mechanism of Gd2O2S:Tb3+ green phosphor

To improve the luminescence performance of Gd2O2S:Tb3+, Gd2O2S:Tb3+, Tm3+, Gd2O2S:Tb3+, Dy3+, Tm3+ and Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 phosphors have been prepared by molten salt method. The samples are characterized using XRD, SEM, TEM, FT-IR, UV-Vis absorption spectroscopy, photoluminescence, cathodoluminescence and thermal stabilization tests. XRD tests and refinement results show that the crystal structure of the phosphor is still the hexagonal Gd2O2S crystalline phase and the lattice parameter decrease due to Dy3+/Tm3+ occupying the Gd3+ sites. SEM images and mapping of each element show that the partical grain and all expected elements distribute uniformly. TEM results illustrate that SiO2 coating is in an amorphous form on the surface of the powder grains. FT-IR tests indicate that SiO2 is present on the powder surface through Si-O-Gd bonding. The results of photoluminescence and cathodoluminescence show that the luminescence intensity increase 50% while adding Tm3+ into Gd2O2S:Tb3+, Gd2O2S:Tb3+, Dy3+ phosphors caused mainly by the energy transfer from Dy3+/Tm3+ to Tb3+. The core-shell structure of Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 has better photoluminescence and cathodoluminescence and the fluorescence lifetime remains unchanged while SiO2 coats phosphor. And it has good thermal stability. Its luminescence intensity at 425 K reaches 71.4% of that at room temperature, which is better than the corresponding value (46.4%) for the uncoated sample.