Energy-splitting from persistent luminescence nanoparticles with trivalent Cr ions for ratiometric temperature sensing.

MgGaO (MGO) with the spinel structure exhibits abundance defects and could achieve the modulation of emission by ion doping as persistent luminescence nanoparticles (PLNPs). Here, we introduced Cr ions into MGO to achieve near-infrared (NIR) emission, and Pr ions to tune the lattice environment for enhanced NIR emission. The optimal composite, MgGaO: 0.005Cr, 0.003Pr (MGCP), achieved enhanced NIR emission at 709 nm under 222 nm excitation. The concentration quenching was observed due to electric dipole-quadrupole interaction at high Cr and Pr content. The afterglow mechanism was revealed, while the energy-splitting occurs from trivalent Cr ions at 650 and 709 nm, thanks to the complex lattice environment. We observed that the emission at 709 nm decreased, while the satellite signal at 650 nm increased first and then decreased intensity with increasing temperature, due to the intervalence charge transfer for Cr ions at 303-528 K. Ratiometric temperature sensing was therefore realized with superb linearity, high absolute sensitivity at 303 K for 4.18%, and accuracy at 528 K for 2.62 K, confirming with the luminescence intensity ratio at 709 and 650 nm under excitation at 222 nm. Thus, we provide a method with energy-splitting emission of Cr ions to design temperature sensing.