Energy transfer between terbium and europium ions in barium orthosilicate phosphors obtained from sol-gel route
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The present paper reports on the energy transfer mechanism between Eu3+ and Tb3+ in barium orthosilicate obtained from the sol-gel route, when both activators concentration is varied. The synthetic methodology was adjusted to provide high crystalline and monophasic Ba2SiO4. In the emission spectra under 250 nm excitation, both Eu3+ (D-5(0)-> F-7(J)) and Tb3+ (D-5(3)-> F-7(J) and D-5(4)-> F-7(J)) transitions can be observed at low Eu3+ doping concentrations with an unexpected and intense blue emission from Tb3+. However, when the Eu3+ content is higher than that of the Tb3+, just the Eu3+ emission is noticed. Also, it is possible to tune the phosphor emission from red to pink by varying the Eu3+ and Tb3+ content. From the excitation spectra, we inferred that energy transfer (ET) from Tb3+ to Eu3+ occurs at any doping situation, nonetheless, the opposite process happens just when both activators amount is similar. An approach using the Tb3+ and Eu3+ lifetimes and the Eu3+ quantum efficiency confirms this observation, indicating that not only the matrix act as sensitizer to the Eu3+ ions, but also Tb3+ ions contribute by increasing the Eu3+ quantum efficiency in up to 20%. Finally, by using the Van Uitert theory, it was found for this system that the ET between the two rare-earth ions is dominated by the dipole-dipole mechanism.