A spectroscopic study of the green (4S3/2 4I15/2) and blue (2P3/2 4I11/2) 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 4I13/2 for the green emission and a three-step absorption process via 4I13/2 and 4S3/2, for the blue emission. The excited-state energy transfer prevails over the excited-state absorption at high concentration (5 at.%).