Energy transfer mechanism for downconversion in the (Pr3+, Yb3+) couple

Downconversion of one visible photon into two infrared photons has been reported for the lanthanide ion couple (Pr3+, Yb3+) in a variety of host lattices. The mechanism responsible for downconversion is controversial and has been reported to be either a two-step energy transfer process (via two first-order transfer steps, the first being cross...