Tuning the emission half-peak width of CaMgSi2O6:Cr3+ from 138 nm to 393 nm by controlling the Cr3+ concentration

Broadband near-infrared (NIR) phosphors play a crucial role in the development of next-generation smart NIR light sources based on blue light-emitting diodes (LEDs). The emission bandwidth is an important parameter for evaluating the performance of these phosphors. Herein, an ultra-broadband NIR phosphor CaMgSi ₂O ₆:Cr ³⁺ (CMSO:Cr), with a tunable emission band and a full width at half maximum (FWHM) ranging from 138 nm to 393 nm, is obtained by adjusting the doping concentration of Cr ³⁺. In the low-concentration doped sample, a single emission peak at 785 nm is observed. When the concentration of Cr ³⁺ exceeds 1.0 at%, emissions at both 785 nm and 980 nm are detected. The emission peak at 785 nm originates from the [MgO ₆ ](Ⅰ) octahedron within the CMSO structure. On the other hand, the emission peak at 980 nm is attributed to the presence of a twisted octahedron [MgO ₆](Ⅱ), which is caused by defects and vacancies resulting from the charge imbalance when Mg ²⁺ ions are replaced by Cr ³⁺ ions. The Cr ³⁺ ion primarily occupies the [MgO6](Ⅰ) site in the lower-concentration doped sample, which explains the photoluminescence peak at 785 nm. With the increase in the concentration of Cr ³⁺ ions, more and more Cr ³⁺ ions preferentially occupy the [MgO ₆ ](Ⅱ) octahedral sites, leading to the broad emission at 980 nm. A novel NIR phosphor light source was fabricated by combining a blue chip with CMSO:Cr phosphor. Driven by a current of 60 mA, the NIR light output power of 5.89 mW and 0.76 mW is achieved by using CMSO:0.015Cr and CMSO:0.04Cr, respectively. This work demonstrates that new luminescent centers can be generated by substituting heterovalent ions, resulting in broadened emission spectra.