Site-selective upconversion excitation of Er3+:KYF4

Abstract

A spectroscopic study of the green (⁴S_3/2 ⁴I_15/2) and blue (²P_3/2 ⁴I_11/2) emissions from Er³⁺:KYF₄ induced by a red tunable laser excitation is realized at liquid nitrogen temperature, for two Er³⁺ concentrations: 0.1 and 5 at.%. The emission spectrum can only be accurately interpreted by considering that it is due to two sites, whose contributions are successfully isolated using a two-step absorption process via ⁴I_13/2 for the green emission and a three-step absorption process via ⁴I_13/2 and ⁴S_3/2, for the blue emission. The excited-state energy transfer prevails over the excited-state absorption at high concentration (5 at.%).