We provide the first demonstration of pure red emission in the visible light region via three-photon excitation in monodisperse Na3ZrF7:Er nanoparticles (NPs) by using a laser operating in the telecommunication band. NPs of ～22 nm in diameter are synthesized at 260°C by the thermal decomposition method. The experimental results reveal that the Na3ZrF7:Er NPs exhibit pure red emission in the visible region under 1480 nm laser excitation, and the emission intensity is significantly influenced by the Er3+ ion concentration. The decay times of the S3/24→F415/2 and F9/24→F415/2 transitions of the Er3+ ions at 540 and 655 nm, respectively, are reduced by increasing the Er3+ ion concentration in the 160.2540 Fluorescent and luminescent materials 160.4760 Optical properties