Molten Salt Synthesis of Broad-Band Near-Infrared InBO3:Cr3+ Submicron Phosphor and Its Luminescent Enhancement by Lanthanide Ion Codoping

Phosphor materials with small particle sizes and high luminescent efficiency are desired for the fabrication of phosphor-converted light-emitting diodes (pc-LEDs). Near-infrared (NIR) pc-LED light sources have great application potential in the food industry and medical fields, which stimulate the extensive exploration of NIR phosphors. In this work, broad-band NIR-emitting InBO3:Cr3+ phosphors with submicron size and spherical morphology are successfully synthesized via the molten salt method. The InBO3:Cr3+ phosphor exhibits a broad emission band covering 700–1000 nm and peaking at ∼820 nm. The maximum emission intensity is obtained for InBO3:0.02Cr3+ with an internal quantum yield (IQY) of ∼62%, which is higher than that of microsized counterparts derived from solid-state reaction. Furthermore, the absorption and emission enhancements are achieved by codoping lanthanide ions into InBO3:Cr3+ submicron phosphors. The codoping of inert La3+ ions can increase the absorption efficiency of InBO3:Cr3+, due to the increased octahedral distortion of Cr3+ sites. The codoping of active Yb3+ ions can significantly enhance the NIR emissions of InBO3:Cr3+ between 950 and 1100 nm. Meanwhile, the increased IQY of ∼73% is achieved for InBO3:0.02Cr3+,0.005Yb3+ simultaneously with suppressed thermal quenching, originating from the effective energy transfer from Cr3+ to Yb3+ ions.