EPR and luminescence studies of the radiation induced Eu 2+ centers in the EuAl 3 (BO 3 ) 4 single crystals

Abstract We have studied the X-ray irradiated EuAl 3 (BO 3 ) 4 single crystals by means of luminescence and electron paramagnetic resonance (EPR) spectroscopy. It was found that the X-ray irradiation modifies the color of the EuAl 3 (BO 3 ) 4 crystal and leads to the formation of a stable Eu 2+ centers from the Eu 3+ centers located in a host matrix. Annealing of the crystal at 600 °C leads to the restoration of the original color and the disappearance of Eu 2+ centers. The EPR and luminescence spectra of the Eu 2+ ion were studied in a wide temperature range. The angular dependence of Eu 2+ EPR spectra is described by an axial spin Hamiltonian characterized by the spin of S = 7/2 with the following parameters: g z = g x = 1.991 (1); b 2 0 = −267,86 (16)*10 −4 cm −1 ; b 4 0 = −4,20 (8)* 10 −4 cm −1 ; b 6 0 = 0,37 (13)* 10 −4 cm −1 ; A (151) = 31,4 (3)* 10 −4 cm −1 ; A (153) = 13,9 (3)* 10 −4 cm −1 . Based on the comparison of spin Hamiltonian parameters of Eu 2+ and Gd 3+ ions, it was concluded that Eu 2+ ion located at the Eu 3+ site in the EuAl 3 (BO 3 ) 4 crystal lattice. Within the framework of the superposition model, the distortions introduced to the local environment by the Eu 2+ and Gd 3+ ions were analyzed. In the luminescence spectra, the bands associated with the Eu 2+ and Eu 3+ ions are detected. The photoluminescence decay kinetics of Eu 3+ -related emission (614 nm) has a single-exponential character, whereas the Eu 2+ -related band (323 nm) possess more complicated decay kinetics behavior that may point to the Eu 2+ excited state ionization and its delayed recombination.