Energy Conversion and Transfer in the Luminescence of CeSc(BO):Cr Phosphor.

Novel near-infrared (NIR) phosphors are in demand for light-emitting diode (LED) devices to extend their suitability for new applications and, in turn, support the sustainable and healthy development of the LED industry. The Cr has been used as an activator in the development of new NIR phosphors. However, one main obstacle for the Cr-activated phosphors is the low luminescence efficiency due to the spin-forbidden d-d transition of Cr. The rare-earth (RE) huntite minerals that crystallize in the form of REM(BO) (M = Al, Sc, Cr, Fe, Ga) have a large family of members, including the rare-earth scandium borates of RESc(BO). Interestingly, in our research, we found that the luminescence efficiency of Cr in the CeSc(BO) host, whose quantum yield was measured at 56%, is several times higher than that in GdSc(BO), TbSc(BO), and LuSc(BO) hosts. Hereby, the energy conversion and transfer in the luminescence of CeSc(BO):Cr phosphor were examined. The Stokes shift of electron energy conversion within the CrT level for the emission at 818 nm and excitation at 625 nm in CeSc(BO) host was evaluated to be 3775.1 cm, and the super-large splitting energy of the F and F sub-states of the Ce 4f state, about 3000 cm, was found in CeSc(BO) host. The typical electronic thermal vibration peaks were observed in the excitation spectra of CeSc(BO):Cr. On this basis, the smallest phonon energy, around 347.7 cm, of the CeSc(BO) host was estimated. Finally, the energy transfer that is responsible for the far higher photoluminescence of Cr in CeSc(BO) than in other hosts was proven through the way of Ce emission and Cr reabsorption.