Tunable NIR emission in Cr3+ activated (La,Gd)Sc3(BO3)4 based on host crystal engineering strategy

This study systematically investigates the structural and luminescent characteristics of LaSc 3 (BO 3 ) 4 :x %Cr 3+ and La (1-y) Gd y Sc 3 (BO 3 ) 4 :1.0 %Cr 3+ phosphors. X-ray diffraction confirms the formation of a pure hunter-type structure for all samples, with Cr 3+ occupying Sc 3+ sites and Gd 3+ substituting La 3+ , inducing lattice contraction. Luminescent analysis reveals that LaSc 3 (BO 3 ) 4 :Cr 3+ exhibits an emission at 980 nm under 430 nm excitation, attributed to the 4 T 2 → 4 A 2 transition of Cr 3+ in a weak crystal field. The substitution of Gd 3+ enhances photoluminescence intensity by 2.15-fold, and blue-shifts emission to 938 nm because of increased crystal field splitting and structural rigidity. The broadened full width at half maximum is also formed due to the enhanced degree of disorder in GdSc 3 (BO 3 ) 4 . Thermal stability studies show that GdSc 3 (BO 3 ) 4 :Cr 3+ retains 49 % intensity at 540 K, outperforming LaSc 3 (BO 3 ) 4 :Cr 3+ (41 %), supported by higher activation energy (ΔE = 0.338 eV vs. 0.296 eV). The improved thermal resistance is linked to lattice rigidity and reduced electron-phonon coupling. NIR-pc-LEDs fabricated with GdSc 3 (BO 3 ) 4 :Cr 3+ demonstrate superior radiant flux (68.7 mW at 200 mA) compared to La-based devices. These results highlight the critical role of host lattice engineering in optimizing Cr 3+ luminescence for high-power NIR applications.