Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr³⁺-activated Mg₂SiO₄ infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr³⁺ emitters in two different Mg sites in the Mg₂SiO₄ lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg₂SiO₄:Cr³⁺ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr³⁺-doped phosphors.