Luminescence Upconversion Under High Pressure in Ni 2+ Doped CsCdCl 3

The near-infrared to visible upconversion properties of Ni 2+ doped CsCdCl 3 are studied as a function of hydrostatic pressure. At 15 K and ambient pressure, near-infrared excitation of Ni 2+ around 810 nm leads to upconversion luminescence centered around 610 nm. Due to the increase of the ligand field strength with increasing pressure, the emission band moves to higher energies with a rate of 19 cm m 1 /kbar, and at 46 kbar it is centered around 585 nm. Thus the upconversion luminescence undergoes a color change from red to yellow in the 1 bar-46 kbar pressure range. The 15 K pressure-dependent upconversion excitation spectra reveal a slight red-shift of m 4 cm m 1 /kbar of the upconversion relevant 3 T 2g M 1 T 2g excited state absorption (ESA) transition, and this is related to a reduction of the Racah B and C parameters, caused by an increasing degree of covalency in the Ni 2+ -Cl m interaction towards higher pressures. Thus, with upconversion luminescence excitation spectroscopy we can obtain information about the pressure-dependence of an ESA transition. The pressure-induced intensity redistributions within this excitation spectrum are indicative of an increasing spectral overlap of 3 T 2g M 1 T 2g ESA with 3 A 2g M 3 T 1g ground state absorption, potentially leading to more efficient upconversion at higher pressures than at ambient pressure. Keywords: High PressureUpconversionLuminescenceOptical SpectroscopyNi2+