The kinetic limitation of anti-Stokes luminescence of Er3+ and Yb3+ doped infrared upconversion materials

Infrared-to-visible wave-length conversion in the Yb3+-Er3+ doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the range of 900-1000 nm of an IR-photon is first absorbed by Yb3+ ion as a sensitizer attributed to the resonant energy transition in Er3+ ion from S-4(3/2) --> I-4(15/2) and F-4(9/2) --> I-4(15/2), respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from I-4(11/2) and I-4(13/2), cross-relaxation from S-4(3/2) and F-4(9/2) are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics of this rare-earth system.