The Luminescence Spectra of Bi3+ Ions in MgO and CaO

The details of the luminescence spectra of Bi3+ in MgO and CaO have been examined over a wide range of temperature. It is found thatemission from both 3P0 and 3P1 excited states to the 1S0 ground state occurs, the former forbidden transition dominating at low temperatures and the latter at high temperatures. The bands can be resolved from one another, thus permitting the intensities and lifetimes of each transition to be followed. These measurements show that over a substantial temperature range the two excited states are in thermal equilibrium, and the decay characteristics are examined with theaid of a model developed in the Appendix. The radiative lifetimes of the 3PI and 3P0 states are found to be 4 × 10−8 and 2.9 × 10−3 s, respectivelyin MgO, and 2 × 10−9 and 3.8 × 10−3 s in CaO. With the aid of the discovery of the true zero‐phonon line for the 3P0 → 1S0 transition in CaO: Bi at 383.98 nm, the form of the vibronic series for this transitioncan be interpreted. The forbidden transition is made slightly allowed by a combination of a static perturbation and coupling to a vibrational mode which mixes the 3P0 and 3P1 states. This interpretation is consistent with the results of magnetic‐field enhancement of the zero‐phonon line intensity reported by Runciman et al.