We have performed a spectroscopic study of ErxY1-x[(p-CF3-C6F4)(2)PO2](3) aimed at understanding nonradiative de-excitation mechanisms. These fluorinated compounds have a long lifetime for the erbium I-4(13/2) - I-4(15/2) emission at lambda similar to 1540 nm, but the lifetime increases with decreasing x. We have studied the lifetime as a function of morphology, temperature, and high hydrostatic pressure. We have demonstrated the occurrence of energy migration and calculated the corresponding activation energy. Moreover, using high pressure techniques, we provide evidence that cross-relaxation involving energy transfer from an excited erbium in the I-4(13/2) promoting a neighbor in the same state to I-4(9/2) is the dominant mechanism at ambient conditions for short erbium-erbium distances. The model explains the observed dynamics of excited states in the series and is tested against the Yb[(p-CF3-C6F4)(2)PO2](3) compound.