Origin of the infrared to visible upconversion mechanisms in Nd3+-doped potassium lead chloride crystal

The infrared to visible upconversion mechanisms of Nd3+ ions in potassium lead chloride crystal have been investigated at liquid nitrogen temperature (LNT). We have observed upconversion luminescence when pumping into both 4F3/2 and 4F5/2 bands and off-resonance, at 851 and 856 nm. The main bands appearing in the emission spectra are two blue bands located at 420 and 435 nm, corresponding to transitions 4D3/2 → 4I13/2 and 2P1/2 → 4I9/2 respectively, and green, orange and red emissions, located at 535, 595 and 668 nm, corresponding to 4G7/2-4G9/2 → 4I9/2, 4I11/2, 4I13/2 transitions, respectively. The results show that, upon excitation of either the 4F3/2 or 4F5/2 band at LNT, two- and three-body energy transfer upconversion process are responsible for the emissions coming from levels 4G7/2-4G9/2 (535, 595, and 668 nm) and 4D3/2 (420 nm), respectively. However, the experimental data indicate that the mechanisms leading to the luminescence coming from level 2P1/2 depend on the pumping wavelength and sample temperature.