Luminescence lines under pressure

The most common pressure sensor for optical studies is ruby (AI2O3 Cr3+, Piermarini et al. (1975)), whose strong Ri and R2 luminescence line shifts under pressure have been calibrated up to 180 GPa at room temperature (Mao et al., 1978 Mao, 1989). At low temperatures the line position has to be corrected by a known temperature-induced shift (Noack and Holzapfel, 1979). Besides ruby also other sensors utilizing rare-earth ions have been proposed and discussed in literature (Shen et al., 1991). In most of these cases the pressure induced shifts of luminescence lines are used to determine the pressure (see sect. 4.5). 

Throughout the 1920s and 1930s the Department of Experimental Physics at the University of Warsaw was an active center for studies on luminescence under S. Pienkowski. During most of this period, Jabtonski worked both theoretically and experimentally on fundamental problems of photoluminescence of liquid solutions as well as on the effects of pressure on atomic spectral lines in gases. The problem that intrigued Jabtonski for many years was the polarization of photoluminescence of solutions. To explain the experimental facts, he distinguished the transition moments In absorption and In emission and analyzed various factors responsible for the depolarization of luminescence. 

Usually, it is assumed that pressure effects under the hydrostatic limit are isotropic, which causes a proportional decrease of all distances in the lattice without a change in the local symmetry of the Ln ion. As the result, a standard assumption is that angular factors C (0, (j>) in the crystal-field Hamiltonian are pressure independent and that the only pressure-sensitive parameters are the Slater integrals, spin-orbit coupling, and radial crystal-field parameters (R)- Then, in most cases, pressure causes small linear shifts of the sharp-lines luminescence related to f-f transitions in the Ln " and Ln ions. 

The luminescence spectra of Ca W04 Tb obtained at different pressures are presented in Fig. 4.31b. Under ambient conditions, the emission consists of sharp lines related to transitions from the and D4 excited states. The lines with peaks at 382,414,436,458, and 470 nm correspond to the —> Fj(J = 2, 3,4, 5, and... 

Spectacular results have been obtained by Srivastava et al. [207] in cubic Y2O3 Pr ". Under ambient pressure, the luminescence spectrum of Y203 Pr consists of sharp lines peaking at 600-700 nm related to the radiative transition D2 —> in... 

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