Energy Conversion and Transfer in the Luminescence of CeSc3(BO3)4:Cr3+ Phosphor

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 Cr3+ has been used as an activator in the development of new NIR phosphors. However, one main obstacle for the Cr3+-activated phosphors is the low luminescence efficiency due to the spin-forbidden d-d transition of Cr3+. The rare-earth (RE) huntite minerals that crystallize in the form of REM3(BO3)4 (M = Al, Sc, Cr, Fe, Ga) have a large family of members, including the rare-earth scandium borates of RESc3(BO3)4. Interestingly, in our research, we found that the luminescence efficiency of Cr3+ in the CeSc3(BO3)4 host, whose quantum yield was measured at 56%, is several times higher than that in GdSc3(BO3)4, TbSc3(BO3)4, and LuSc3(BO3)4 hosts. Hereby, the energy conversion and transfer in the luminescence of CeSc3(BO3)4:Cr3+ phosphor were examined. The Stokes shift of electron energy conversion within the Cr3+ 4T2g level for the emission at 818 nm and excitation at 625 nm in CeSc3(BO3)4 host was evaluated to be 3775.1 cm−1, and the super-large splitting energy of the 2F5/2 and 2F72 sub-states of the Ce3+ 4f1 state, about 3000 cm−1, was found in CeSc3(BO3)4 host. The typical electronic thermal vibration peaks were observed in the excitation spectra of CeSc3(BO3)4:Cr3+. On this basis, the smallest phonon energy, around 347.7 cm−1, of the CeSc3(BO3)4 host was estimated. Finally, the energy transfer that is responsible for the far higher photoluminescence of Cr3+ in CeSc3(BO3)4 than in other hosts was proven through the way of Ce3+ emission and Cr3+ reabsorption.

Developing the Na2CaZr2Ge3O12:Cr3+ Garnet Phosphor for Advanced NIR pc-LEDs in Night Vision and Bioimaging

“…This approach possesses distinct advantages such as the same compact size, long lifetime, and even less energy consumption compared with direct-emitting NIR LEDs. They also have the added benefit of an easily adjustable emission spectrum, including the ability to cover nearly the entire NIR region similar to the incandescent lamps using a single broad-emitting phosphor. − These attributes make them ideal for future integration into portable smart devices, enabling a wide array of applications.…”