Infrared to visible and ultraviolet upconversion processes in Nd-doped potassium lead chloride crystal

Infrared to visible and ultraviolet upconversion in Nd³⁺ doped KPb₂Cl₅ crystal is reported. Three intense bands have been observed at 535, 595, and 668 nm coming mainly from levels ⁴G_7/2–⁴G_9/2, together with emissions at 362, 388, 420 and 456 nm coming from level ⁴D_3/2, and a peak at 435 nm, corresponding to the ²P_1/2 → ⁴I_9/2 transition. A study of the upconversion mechanisms has been carried out that includes the upconversion emission dependence on the wavelength and intensity of the pumping light together with a comparison of the luminescence decays after infrared excitation and after direct one photon excitation of the emitting levels. The results indicate that two- and three-body energy transfer upconversion processes are responsible for emissions from levels ⁴G_7/2–⁴G_9/2 and ⁴D_3/2 respectively, while level ²P_1/2 is populated by either energy transfer upconversion or excited state absorption depending on the pumping wavelength.