Fine tunable red-green upconversion luminescence from glass ceramic containing 5%Er³⁺:NaYF₄ nanocrystals under excitation of two near infrared femtosecond lasers

In this paper, we report fine tunable red-green upconversion luminescence of glass ceramic containing 5%Er³⁺: NaYF₄ nanocrystals excited simultaneously by two near infrared femtosecond lasers. When the glass ceramic was irradiated by 800 nm femtosecond laser, weak red emission centered at 670 nm was detected. Bright red light was observed when the fs laser wavelength was tuned to 1490 nm. However, when excited by the two fs lasers simultaneously, the sample emitted bright green light centered at 550 nm, while the red light kept the same intensity. The dependences of the red and the green light intensities on the two pump lasers are much different, which enables us to manipulate the color emission by adjusting the two pump laser intensities, respectively. We present a theoretical model of Er³⁺ ions interacting with two fs laser fields, and explain well the experimental results.