Tunable blue-green emission and energy transfer properties in Ba2SiO4:Tb3+ obtained from sol-gel method

Herein, we introduce an adapted sol-gel synthesis of blue-green-emitting phosphors based on Ba2SiO4:Tb3+, which were obtained in a quite-soft calcination condition (1100 °C/2 h) as a monophasic crystalline phase, space group Pmcn (62), characterized by high-agglomerated particles. The optical band gap value decreases as the amount of Tb3+ increases, from 5.65 eV (undoped) to 4.40 eV (5 %-doped). All doped samples are excited by UV radiation (250 nm), emitting in the blue and green spectral region as a result of the Tb3+ transitions arising from the 5D3 and 5D4 excited levels, respectively. Yet, the overall emitted color of the phosphor is tuned by the Tb3+ concentration since the increase of the activator amount dislocates the emission color from blue toward green due to a dipole-dipole energy transfer between two close Tb3+ ions. The emission quantum efficiency of the 5D4 state is a function of the emission intensity and it enhances up to the 4 %-doped sample. A new approach to calculate the 5D3 state quantum efficiency of Tb3+ is also proposed and these values decrease from 95.3% to 42.4% as the doping amount enhances from 0.1 up to 5%. Thus, both the green-blue color tunability and the high quantum efficiency qualify this material for future photonic applications.