Mn²⁺-Activated Alkali Lithooxidosilicate Phosphors as Sustainable Alternative White-Light Emitters

Eu²⁺-activated alkali lithooxidosilicates have emerged as promising candidates for narrow-band cyan and green-emitting phosphors for human-centered lighting. Despite the vivid research on Eu²⁺-activated alkali lithooxidosilicates, little to nothing is known about the possible luminescence with other activator ions than Eu²⁺. The more abundant transition metal ion Mn²⁺ is a potential alternative emitter with tunable emission over the visible spectral range. Mn²⁺-activated alkali lithooxidosilicates show two emission bands in the green and red spectral range, respectively, making them intriguing candidates for one-component phosphor-converted white light-emitting diodes. A total of seven Mn²⁺ activated compounds were prepared to elucidate possible trends. The results show that the ratio between green and red emission correlates to the size of the available activator sites and is easily controlled by the composition of the alkali lithooxidosilicate host compounds. Temperature-dependent luminescence studies reveal that thermal quenching occurs slightly above room temperature for those compounds, which may be connected to the comparably low band gaps for silicates (E_g < 6 eV) and a consequent thermal ionization of excited electrons into the conduction band. Overall, this study comprises the first class of compounds with efficient tailored white-light emission based on Mn²⁺ within one host compound.