Blue light excitable efficient down-conversion photoluminescence of Yb3+ and Er3+ in ultra-wide NIR region via Cr3+-Yb3+-Er3+ energy transfer in KAlP2O7 and multifunctional applications

Abstract

Broadband near-infrared (NIR) phosphors have gained growing interest in applications such as food detection, plant growth and night vision lighting. However, designing NIR phosphors with large full width at half maximum (FWHM) is challenging. In this study, we introduce a novel blue light excitable Cr³⁺-Yb³⁺-Er³⁺ tri-doped KAlP₂O₇ (KAPO) phosphor, which exhibits luminescence in ultra-wide NIR region, including broadband NIR-II luminescence with the FWHM of 302 nm and sharp NIR-III luminescence at 1538 nm. Fluorescence decay curves confirmed the presence of energy transfer. In addition, the NIR optical thermometry was developed using the non-thermally coupled energy states of ⁴T₂→⁴A₂ (Cr³⁺) and ⁴I_13/2→⁴I_15/2 (Er³⁺), with the highest absolute (S_A) and relative sensitivity (S_R) values determined to be 122.2 × 10⁻⁴ K⁻¹ (T = 473 K) and 0.76% K⁻¹ (T = 448 K), respectively. In addition,the prepared phosphor can be efficiently excited by various wavelengths including 377 nm ultraviolet light, 468 nm blue light, and 808/980 nm near infrared light, suggesting its promising applications in anti-counterfeiting. The NIR phosphor-converted LED (pc-LED) was fabricated using KAPO: 0.01Cr³⁺, 0.002Yb³⁺, 0.01Er³⁺ phosphor and a 470 nm LED chip, demonstrating notable potential in night vision technology.