Spectral Broadening in Cr³⁺-Doped Sr_0.92Mg_0.91Al_10.1O₁₇ NIR Phosphor Realized by Multi-crystallographic Site Occupation

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) play an important role in nondestructive testing, medical imaging, food analysis, and so on. Broadband NIR phosphors are needed in order to cover the characteristic wavelengths of various matters. In this paper, a NIR phosphor, Sr_0.92Mg_0.91Al_10.1O₁₇ (SMAO):Cr³⁺, with a full width at half maximum (FWHM) of 12–102 nm is achieved as a function of Cr³⁺ concentration. Two Cr³⁺ sites are observed by means of excitation spectra and fluorescence decay curves. The spectral broadening with the increase of Cr³⁺ concentration is attributed to the increase of occupation ratio on the weak crystal field site by Cr³⁺. In addition, the difference in thermal stability between ²E and ⁴T₂ is employed to conduct the temperature measurement with a relative sensitivity of 0.43% K^–1 at 270 K. A NIR pc-LED is fabricated using SMAO:0.03Cr³⁺ phosphor combined with a 395 nm LED chip with radiation flux of 2.2 mW@10 mA and 15 mW@100 mA.