Abstracts 2002

Abstract of Publication No. 432

Oliver S. Wenger, G. Mackay Salley and H. U. Güdel
Effects of High Pressure on the Luminescence and Upconversion Properties of Ti2+-Doped NaCl
J. Phys. Chem. B 106, 10082-10088 (2002)      Full Text (PDF)      DOI-Link      Supplementary Data (PDF)     

Abstract: The luminescence and upconversion properties of 0.8% Ti2+-doped NaCl at 15 K are studied as a function of external hydrostatic pressure. Luminescence band maxima shifts are analyzed with a ligand field point charge model, allowing an estimate of the compressibility of the spectroscopically active TiCl64- unit in the NaCl host matrix. The pressure dependencies of the vibrational fine structures in the two Ti2+ luminescence bands are analyzed and interpreted in terms of pressure-induced changes in equilibrium distortions and force constants of the emitting electronic states 3T2g(t2geg) and 3T1g(t2geg). Time-resolved luminescence measurements are used to study the effects of pressure on the excited-state dynamics. 15 K near-infrared excitation at 9399 cm1 leads to upconversion luminescence in the red spectral region both at ambient pressure and 34 kbar. On the basis of time-dependent upconversion luminescence experiments, two fundamentally different upconversion mechanisms are found to be dominant under these two experimental conditions. In particular, pressure is found to switch on an efficient upconversion mechanism, which is inactive at ambient pressure, leading to an estimated order-of-magnitude enhancement of the overall upconversion efficiency at 34 kbar. This additional mechanism involves energy transfer (ET) between two excited Ti2+ ions. Its occurrence only at high pressure is interpreted in terms of a strongly pressure-dependent spectral overlap integral governing the efficiency of the ET step.

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