Abstract
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.