Energy transfer and thermal stability in Bi3+/Eu3+ co-doped germanium-borate glasses for organic-resin-free UV LEDs

In this paper, novel Bi3+/Eu3+ co-doped white-emitting germanium-borate glasses were successfully prepared by the melt-quenching method. Their luminescent properties were evaluated using the transmission spectra, photoluminescence excitation, and emission spectra (with a temperature range of 298-573 K), and lifetime decay curves. Due to the efficient energy transfer from Bi3+ to Eu3+, tunable emitting color between the bluish-green and the orange-red region has been obtained by varying the content of Eu3+ (0-7%). Interestingly, a perfect white-light emission with CIE coordinates (X = 0.356, Y = 0.325) is realized upon the excitation at 345 nm light in the Bi3+/Eu3+ co-doped sample. More remarkably, the white-light emission glass maintains excellent color stability even at 423 K. Our results indicate that the Bi3+/Eu3+ co-doped germanium-borate glasses may be used as a potential single-phased white light-emitting matrix material for the UV converted organic-resin-free WLEDs in the future.