Energy Conversion and Transfer in the Luminescence of CeSc 3 (BO 3 ) 4 :Cr 3+ 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 3+ has been used as an activator in the development of new NIR phosphors. However, one main obstacle for the Cr 3+ -activated phosphors is the low luminescence efficiency due to the spin-forbidden d-d transition of Cr 3+ . The rare-earth (RE) huntite minerals that crystallize in the form of REM 3 (BO 3 ) 4 (M = Al, Sc, Cr, Fe, Ga) have a large family of members, including the rare-earth scandium borates of RESc 3 (BO 3 ) 4 . Interestingly, in our research, we found that the luminescence efficiency of Cr 3+ in the CeSc 3 (BO 3 ) 4 host, whose quantum yield was measured at 56%, is several times higher than that in GdSc 3 (BO 3 ) 4 , TbSc 3 (BO 3 ) 4 , and LuSc 3 (BO 3 ) 4 hosts. Hereby, the energy conversion and transfer in the luminescence of CeSc 3 (BO 3 ) 4 :Cr 3+ phosphor were examined. The Stokes shift of electron energy conversion within the Cr 3+ 4 T 2g level for the emission at 818 nm and excitation at 625 nm in CeSc 3 (BO 3 ) 4 host was evaluated to be 3775.1 cm -1 , and the super-large splitting energy of the 2 F 5/2 and 2 F 72 sub-states of the Ce 3+ 4f 1 state, about 3000 cm -1 , was found in CeSc 3 (BO 3 ) 4 host. The typical electronic thermal vibration peaks were observed in the excitation spectra of CeSc 3 (BO 3 ) 4 :Cr 3+ . On this basis, the smallest phonon energy, around 347.7 cm -1 , of the CeSc 3 (BO 3 ) 4 host was estimated. Finally, the energy transfer that is responsible for the far higher photoluminescence of Cr 3+ in CeSc 3 (BO 3 ) 4 than in other hosts was proven through the way of Ce 3+ emission and Cr 3+ reabsorption.