Upconversion processes in Nd3+-doped fluorochloride glass

Infrared (IR) to visible (VIS) and ultraviolet (UV) upconversion in Nd3+-doped fluorochloride glass has been observed between 4.2 and 300 K under continuous wave (cw) and pulsed IR laser excitation in resonance with the 4F3/2 and 4F5/2 levels. The emission spectra have UV bands at 359 and 383 nm and VIS bands located around 416, 452, 527, 589, and 660 nm. The green, yellow, and red emissions are attributed to transitions from the 4G7/2 excited state. The excitation spectra of the upconverted emissions which are similar to the one-photon absorption spectrum, together with the features appearing in the decays of these emissions, indicate that an energy transfer upconversion (ETU) process seems to be responsible for the VIS luminescence observed, though other possible mechanisms cannot be disregarded. Referring to the blue and UV bands, the most probable origin of the upconverted fluorescence seems to be the 4D3/2, 4D5/2, 4D1/2 levels. In the last, the participation of three neodymium ions is necessary in the ETU process.