Cooperative radiative and nonradiative effects in K_2NaScF_6 codoped with V~(3+) and Er~(3+)

摘要

K_2NaScF_6 crystals codoped with V~(3+) and Er~(3+) exhibit some novel cooperative near-IR to visible upconversion processes at cryogenic temperatures.V~(3+) mainly acts as a broadband sensitizer.The V~(3+)~3T_(1g)->~3T_(2g) excitation between 13500 and 15500 cm~(-1),after fast relaxation to V~(3+1)T_(2g),can be transferred to Er~(3+4)I_(11/2),and then upconversion takes place.Four upconversion mechanisms are idnetified and characterized.For narrow-band laser excitation the overall efficiency of the upconversion processes is low.However,at 12 K broadband excitation,such as in a lamp,between 12000 and 14500cm~(-1) the number of emitted visible photons is roughly doubled by codoping V~(3+) in addition to Er~(3+).