Mixing of the f2(1S0) and 4f5d states of Pr3+ in BaSO4 under high pressure

The high-lying states of Pr3+ have exhibited efficient quantum splitting via cascade emission in a number of hosts. This occurs when the f2(1S0) state lies below the 4f5d state. The close energy proximity of these two states results in significant mixing which, because of the different parity of these states, has important consequences concerning their optical properties. This is examined for Pr3+ in BaSO4, where the energy splitting is only about 325 cm−1, utilizing high pressures to tune the relative energies of these states. Because of their high excitation energies, conventional excitation using diamond anvil cells is not possible. This problem is solved in two ways, one utilizing two-photon excitation from the 1D2 intermediate state and the other using a sapphire anvil cell with 193 nm excimer laser pumping. The transition energies and relative intensities of both the f2(1S0) and 4f5d states are studied as a function of pressure up to 100 kbar and the emission lifetimes are obtained up to 89 kbar. An anomalous increase in the energy of the lowest component of the 4f5d state with pressure and an associated reduced mixing is observed based both on the static and dynamic spectroscopy. A simple model for the mixing is applied to describe both the relative intensities and lifetimes. The resulting fit yields the pressure dependence of the energy splitting and the state mixing parameters.