Bi³⁺ occupancy rearrangement in K_2-xA_xMgGeO₄ phosphor to achieve ultra-broad-band white emission based on alkali metal substitution engineering

Ultra-broad-band white emitting phosphors have a wide application prospect in the new generation of illumination systems. Due to the sensitivity of Bi³⁺ to the surrounding environment, it exhibits different luminescence properties in different crystallographic sites, which makes it easy to achieve white emission. Cationic substitution engineering is the most effective strategy for controlling the environment around Bi-site and realizing the spectrum tuning. Herein, we conducted substitution engineering in K₂MgGeO₄:Bi³⁺ (KMGO:Bi³⁺) that uses alkali metal A⁺ (A = Li, Na, Rb) to substitute K⁺. The difference in emission spectrum excited at various wavelengths is related to extra luminescent centers generation and Bi³⁺ occupancy rearrangement in KMGO:Bi³⁺ under the influence of Li⁺ and Na⁺, which also leads to the expansion of full widths at half-maximum (FWHM) to 204 nm forming a bright white emission. Besides, the modulation of Rb⁺ increases the activation energy and enhances its thermal stability to 88.66%. The high R_a values (93.4) of the fabricated WLED indicate that K_1.456Na_0.54MgGeO₄:0.004Bi³⁺ could be used as a single-component white phosphor in solid-state lighting. Our research shows that alkali metal substitution engineering is of great significance to controlling the luminescence emission and improving the thermal stability of luminescent materials.