Phonon-Assisted Energy Transfer between Trivalent Rare Earth Ions

Abstract

Nonresonant phonon-assisted energy transfer between trivalent rare earth ions is studied using Y₂O₃ as the host crystal. The transfer probabilities are obtained from the analysis of the decay rates of donor luminescence for various combinations of donor and acceptor ions in which energy gap, i.e. mismatch of energy, is varied in a wide range up to 4000 cm⁻¹. The probabilities are decreased exponentially with the increase of energy gap in agreement with the theory of Miyakawa and Dexter. The observed value of the parameter expressing the exponential dependence agrees with the theoretically estimated value. The temperature dependence of the probabilities presents the direct evidence that the mismatch of energy is compensated by the emission of phonons. It is revealed that the phonon of about 400 cm⁻¹ which produces the highest intensity in vibronic sidebands contributes dominantly to the phonon-assisted process.