Two-wavelength two-photon process for optical selection of rare-earth ions

• Two-photon process is aptly proposed to optically select rare earth ions.
• The two-photon process is realized by simultaneous two-wavelength excitation.
• Er3+ ions in NaYF4 could be selectively excited, producing violet emission.
• The strategy is verified by spectra, power dependence and lifetime measurements.

The past decades has witnessed the blossom of upconversion, which is based on the ground state absorption (GSA) and excited state absorption (ESA) processes. Herein, we propose a brief strategy based on two-photon process with two simultaneous excitation wavelength for optical selection of rare earth (RE) ions. RE ion can be transferred to its intermediate state with resonant frequency from the first laser, and then furthered to the target state with the second laser of appropriate frequency, and every ion is separately excited by simultaneous two-wavelength independently. Herein, the resulting 2H9/2 → 4I15/2 transition of Er3+ in NaYF4 microprisms is employed as a monitoring probe, and this two-photon process is demonstrated by the excitation and emission spectra, and further verified by the dependences on excitation power and the luminescence decay curves. This conception will also provide a new strategy on precise optical selection of RE ions, especially for quantum information technology.