Design of a Novel Near-Infrared Phosphor by Controlling the Cationic Coordination Environment

Phosphors with the emission spectra located at the biological window I (650–950 nm) are significant for biological imaging. In this work, a series of deep red and near-infrared phosphors InMgGaO 4: x Cr 3+ and In 0.9- y MgGaO 4: 0.1Cr 3+, y Al 3+ are designed and successfully synthesized by a high temperature solid state method. InMgGaO 4 is selected as the host considering its special crystal structure that one of the Mg/Ga–O bonds is affected by the surrounding environment. Therefore, when Cr 3+ is substituted into the lattice, the longer Mg/Ga–O bonds are easily broken, which provides a tunable crystal field. The emission spectra of InMgGaO 4: x Cr 3+ cover from 650 to 1200 nm, including one sharp line emission peak (peak 1) and two broad emission bands (peak 2 and peak 3). The Racha parameters D q / B and the decay curves are analyzed to distinguish the origins of these three peaks. Meanwhile, these three emission peaks show different degrees of red shift, which is related to the covalency, crystal field splitting ( D q ), bond breaking of Mg/Ga–O, and decrease of band gap. However, comparing with the luminescent property of Cr 3+ single doped samples, In 0.9- y MgGaO 4: 0.1Cr 3+, y Al 3+ shows a contrasting luminescence property and the reason is analyzed. In summary, the emission spectra of these samples can be tuned between a narrow peak and broad band continuously by controlling the concentration of Cr 3+ ions or Al 3+ ions, which shows a potential application in biological imaging.