Observation and simulation of the energy levels of the trivalent thulium ion in gadolinium oxychloride

The optical absorption of the Tm 3+ ion in the gadolinium oxychloride (GdOCl) matrix in the UV, visible, and NIR range was studied at temperatures between 9 and 300 K. The visible luminescence of GdOCl:Tm 3+ under Ar + ion laser and mercury lamp excitation was recorded at 9, 77, and 300 K, too. The crystal field (CF) splitting of the 3 H 4-6 , 3 F 2-4 , 1 G 4 , 1 D 2 , and 1 I 6 levels of the Tm 3+ ion deduced from the spectra was analysed according to the C 4v point symmetry of the RE 3+ site. The resulting energy level scheme, consisting of 39 levels (i.e. 55 Stark components) out of the total of 70 (91) for the whole 4f 12 configuration, was simulated with the aid of a phenomenological theory taking simultaneously into account both the free-ion and CF effects. The model included 13 adjustable parameters describing the electrostatic (the Racah parameters E 0-3 ) and the configuration interaction (the Trees parameters alpha , beta , and gamma ) as well as the spin-orbit coupling (the coupling constant zeta 4f ). The CF effect was accounted for by the five non-zero B q 4 parameters B 0 2 , B 0 4 , B 4 4 , B 0 6 , and B 4 6 . Good simulation of the experimental energy level scheme was achieved with a root mean square deviation equal to 21 cm -1 . A comparison to the energy level parametrization of the Pr 3+ (4f 2 ), Nd 3+ (4f 3 ), Eu 3+ (4f 6 ), and Tb 3+ ions (4f B electron configuration) in other REOCl matrices shows the consistency of the present results. The systematic trends in the CF effect on the energy level schemes of the RE 3+ ions are discussed, too.