ANALYSIS OF THE 4F(N) ENERGY-LEVEL STRUCTURE OF THE RE(3+) IONS IN REOCL

The optical absorption and luminescence spectra of the tetragonal rare earth oxychlorides (REOCl or REOCl:RE(3+); RE(3+) = Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Ho3+, Er3+, Tm3+) have been measured at selected temperat ures between 9 and 300 K. The energy-level schemes for the 4f(N) (N = 2, 3, 5, 6, 8, 10-12) electron configurations were deduced from the sp ectra and assigned according to the C-4v point symmetry of the RE(3+) + site in REOCl. The complete 4f(N) energy-level schemes were simulate d with a model with 19 parameters taking into account simultaneously b oth the free-ion and crystal-field (c.f.) interactions. Good correlati on was obtained between the experimental and calculated, energy-level schemes of up to 181 c.f. levels. The free-ion electrostatic repulsion interactions and the spin-orbit coupling increase smoothly across the RE(3+) + series with increasing number of electrons. The two-body con figuration interaction terms also behave regularly. The c.f. effect in creases from Pr3+ to Tm3+ although some irregularities exist. This beh avior is in contrast to the trend expected on the grounds of the elect rostatic model suggesting a decrease in the c.f. strength with increas ing number of electrons. The possible interactions leading to this dev iation are discussed.