Luminescence of Ph2+ and Bi3+ Centres in Alkali‐Earth Sulphides and Oxides

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Abstract
Luminescence centres connected with Bi3+ and Pbz+ ions are investigated in CaO, SrO, CaS, and SrS crystals at 5 to 300 K. It is found that the ground state and the two lowest excited states of the Bi3+ as well as the Pb2+ centres correspond to the energy levels of the free impurity ions and have A1g, 3A1U, and 3T1u, symmetries, respectively. Emission is observed which is caused by electronic transitions from both the excited states. The 3A1u, → Alg transition becomes slightly allowed due to the interaction of an electron with the vibrations of T1u, symmetry. The anti‐Stokes and zero‐phonon lines are observed in the vibronic structure of spectra. The main series of lines are caused by the interaction of electrons with the totally symmetric Alg, vibrations. In the emission spectra of CaS: Bi and SrS: Bi electronic transitions in the host lattice perturbed by impurities are also evident besides intra‐centre electronic transitions.