Tunable white light in trivalent europium single doped tin fluorophosphates ultra-low melting glass

In recent years, low melting temperature glasses have received wide attention as the hosts of phosphor-converted light emitting diodes (pc-WLED). In this work, a series of trivalent europium doped tin fluorophosphates glasses were prepared by conventional melting method. Under ultraviolet excitation, the blue-green broadband emission from Sn²⁺ activation centers in the glass matrix and the red emission of Eu³⁺ ions together constituted a cool white luminescence. The spectra analysis was used to demonstrate the energy transfer between Sn²⁺ centers and Eu³⁺ ions. The results showed that Sn²⁺ and Eu³⁺ possessed independent intrinsic emission and mutual energy transfer simultaneously. The ⁵D₄ and ⁵G₂ excited states of Eu³⁺ ion favored the energy transfer to Sn²⁺ center, the ⁵L₆ excited state of Eu³⁺ ion would absorb more of the energy by the Sn²⁺ ground state excitation to contribute on red emission. Therefore, the fluorescent glass can transform cool white light to warm white light by changing the excitation wavelength. The tunable white light is obtained in the WLED devices built with the glass and commercial UV chips.