Effect of Tb3+ concentration in the visible emission of terbium-doped gadolinium oxysulfide microspheres

Experimental data obtained from optical characterization of Gd2O2S:Tb(3+)microspheres were compared with a rate-equation model in order to understand and simulate the emission intensity and color tonality as a function of Tb3+ concentration. The microparticles were prepared by hydrothermal synthesis and characterized by TEM and XRD to confirm spherical microparticles with a hexagonal lattice. Furthermore, fluorescent spectroscopy and rate equation model revealed that the direct energy transfer between Gd3+-> Tb3+ ions and the migration of the excitation energy between Tb3+ play an important role in the luminescence intensity, while the color tonality is mainly governed by the non-radiative relaxation processes between Tb3+ at low concentrations. Finally, our results suggest that the rate equation model provides an efficient alternative to estimate theoretically the maximum doping concentration in oxysulfides before they present quenching of luminescence.