Power switched multiphoton upconversion emissions of Er3+ in Yb3+/Er3+ codoped β-NaYF4 microcrystals induced by 980 nm excitation

Multiphoton upconversion (UC) emissions from the high-energy states ((4)G(9/2), (4)G(7/2), K-2(13/2), and P-2(3/2)) of Er3+ ions were observed under 980 nm excitation. These high-energy excited states were populated by a five-photon or a four-photon UC process conditionally, which depended on the near-infrared (NIR) pump density. Experiments exhibited that the power dependence originated from the varied populating routes of intermediated S-4(3/2) and F-4(9/2) of Er3+ under different NIR pump power. A mechanism of the power density-dependent multiphoton UC processes was proposed based on experimental data and analysis. (C) 2010 Optical Society of America