Synergistic boosting of luminescence intensity in Sr3Lu(PO4)3:Cr3+ via B-site substitution and energy transfer toward multifunctional near-infrared applications

The wideband near-infrared (NIR) phosphors for next-generation intelligent NIR light sources are becoming a research hotspot in the field of luminescent materials due to their potential applications in optical sensing, biological imaging, and smart lighting. This study reports a Cr 3+ -activated A 3 B(PO 4 ) 3 -type (Sr 3 Lu(PO 4 ) 3 ), abbreviated as SLP) near-infrared phosphor. Under 466 nm blue light excitation, SLP:Cr 3+ phosphor exhibits a broad near-infrared emission from 700 to 1200 nm with a peak wavelength at 860 nm, a full width at half maximum (FWHM) of 141 nm, and an initial quantum yield of 31.48%. Structural and spectroscopic characterization confirms that Cr 3+ preferentially occupies the octahedral coordination sites of Lu 3+ in the matrix, forming a weak crystal field environment that favors the spin-allowed 4 T 2 → 4 A 2 transition of Cr 3+ , leading to broad near-infrared emission. Additionally, by substituting Y 3+ for the B-site (Lu 3+ site), the luminescent intensity of the material is significantly enhanced, and the quantum yield is increased to 81.53%. Furthermore, the introduction of Yb 3+ constructs a Cr 3+ →Yb 3+ energy transfer system, further optimizing the luminescent performance. Although the phosphor exhibits severe thermal quenching, the packaged near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) maintain a low surface temperature of 59.5 °C at 500 mA, ensuring reliable operation. The phosphor also exhibits excellent temperature sensitivity (max relative sensitivity: 3.33%·K −1 ) for fluorescence thermometry. Practical applications including invisible QR code encryption, night vision, biological imaging, and long-distance illumination are demonstrated, showcasing the versatility of the developed NIR pc-LED. This work provides a high-performance NIR phosphor candidate for multi-functional smart light sources.