Engineering of K₃YSi₂O₇ To Tune Photoluminescence with Selected Activators and Site Occupancy

The luminescence of rare earth ions (Eu²⁺, Ce³⁺, and Eu³⁺)-doped inorganic solids is attractive for the screening of phosphors applied in solid-state lighting and displays and significant to probe the occupied crystallographic sites in the lattice also offering new routes to photoluminescence tuning. Here, we report on the discovery of the Eu- and Ce-activated K₃YSi₂O₇ phosphors. K₃YSi₂O₇:Eu is effectively excited by 450 nm InGaN blue light-emitting diodes (LEDs) and displays an orange-red emission originated from characteristic transitions of both Eu²⁺ and Eu³⁺, while K₃YSi₂O₇:Ce³⁺ shows green emission upon 394 nm near-ultraviolet (NUV) light excitation. Rietveld refinement verifies the successful doping of the activators, and density functional theory (DFT) calculations further support that Eu²⁺ occupies both K1 and Y2 crystallographic sites, while Ce³⁺ and Eu³⁺ only occupy the Y2 site; hence, the broad-band red emission of Eu²⁺ are attributed to a small DFT band gap (3.69 eV) of K₃YSi₂O₇ host and a selective occupancy of Eu²⁺ in a highly distorted K1 site and a high crystal field splitting around Y2 sites. The white LEDs device utilizing orange-red-emitting K₃YSi₂O₇:Eu and green-emitting K₃YSi₂O₇:Ce³⁺ exhibits an excellent CRI of 90.1 at a correlated color temperature of 4523 K. Our work aims at bridging multivalent Eu²⁺/Eu³⁺ and Ce³⁺ site occupancy in the same host to realize photoluminescence tuning and especially exposes new ways to explore new phosphors with multicolor emission pumped by blue and NUV light for white LEDs.