Abstract

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 S_3/24→F4_15/2 and F_9/24→F4_15/2 transitions of the Er³⁺ ions at 540 and 655 nm, respectively, are reduced by increasing the Er³⁺ ion concentration in the Na₃ZrF₇:Er NPs. The suppressed emission intensity result from the defect-related quenching effect: when trivalent Er³⁺ ions replac tetravalent Zr⁴⁺ ions, extra Na⁺ ions and F⁻ vacancies are formed to re-balance the charge in the Na₃ZrF₇ matrix. The emission color of the Na₃ZrF₇:Er NPs is related to the cross relaxation between Er³⁺ ions. These results provide an important step toward more effective biological imaging and photodynamic therapy by minimizing the scattering of the excitation light and increasing the penetration depth.

© 2016 Chinese Laser Press

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