Quantum efficiency and energy transfer processes in rare-earth doped borate glass for solid-state lighting

Sm3+, Eu3+ and Tb3+ doped borate glass is investigated for its potential as light converting phosphor for solid-state lighting applications. Concentration-dependent luminescence, quantum efficiency and radiative lifetimes are analysed. The luminescence quantum efficiency exceeds values of more than 80%. Cross-relaxation processes in the single-doped glasses result in luminescence quenching for Sm3+ with increasing doping level, whereas for Eu3+ and Tb3+ an increase is observed. In Sm3+/Eu3+ and Tb3+/Eu3+ double-doped glass the energy transfer processes between the rare-earth ions are investigated in detail. The colour coordinate of the Tb3+/Eu3+ double-doped glass can be shifted from the green to the red spectral range by changing the Tb3+-to-Eu3+ ratio in favour of Eu3+. In addition, double doping allows for a change in colour coordinate by using different excitation wavelengths.