Trade-off Lattice Site Occupancy Engineering Strategy for Near-Infrared Phosphors with Ultrabroad and Tunable Emission

Broadband near-infrared (NIR) luminescent materials have received notable attention due to their distinct photophysical properties for designing NIR light-emitting diodes (NIR LEDs). Here, a series of Ca3-xLuxGa2+xGe3-xO12:Cr3+ (CLGGG:Cr3+) (x = 0-1) NIR-emitting garnet phosphors with an emission range of 660-1200 nm are successfully developed and their lattice parameters are structurally analyzed. Upon 460 nm blue light excitation, the NIR phosphors exhibit both a substantial spectral broadening (FWHM: 129 -> 267 nm) and a redshift of 37 nm (766 -> 803 nm) with cosubstitution of [Lu3+-Ga3+] pairs for [Ca2+-Ge4+] sites. Furthermore, their luminescence thermal stability is substantially improved, maintaining approximate to 90% of the original photoluminescence intensity at 150 degrees C, owing to shrinkage of the second coordination sphere and rigid lattice, which are strongly associated with Cr3+ trade-off occupancy and local structure evolutions. The relation between the trade-off site occupation of Cr3+ in GaO6/CaO8 polyhedrons and the NIR emission is also clarified by evaluating the decay and electron paramagnetic resonance behavior of Cr3+ at different sites. The broadband NIR phosphors investigated here can serve as auspicious luminescent converters for phosphor-converted NIR LEDs and can provide an inspiring platform for future studies.