Fast d–f emission in Ce3+, Pr3+ and Nd3+ activated RbCl

In the search for new scintillator materials, Ce3+ doped chlorides are a promising class of materials, combining a high efficiency and fast response time. Even shorter response times may be achieved by replacing Ce3+ by Pr3+ or Nd3+ as the lifetime of the d–f emission is substantially shorter for these ions. Here we report on the luminescence properties of Ce3+, Pr3+ and Nd3+ in RbCl and investigate the potential as a scintillator material. Under UV excitation Ce3+ shows d–f emission between 325 and 425 nm. The emission originates from multiple (differently charge compensated) Ce3+ sites. The luminescence lifetime varies with wavelength and is ∼40 ns for the longer wavelength emission. For RbCl:Pr3+ three d–f emission band are observed between 250 and 350 nm which can be assigned to transitions from the lowest energy fd state to different 3HJ (J = 4–6) states within the 4f2 configuration of Pr3+. The decay time is ∼17 ns. For the Nd3+ activated sample a weak emission band around 220 nm is observed only at 8 K which may be due to d–f emission. The very short lifetime (4 ns) is faster than the radiative lifetime, indicating that the d–f emission is quenched by relaxation to lower lying 4f3 states or by the process of photoionization. Under VUV excitation at wavelengths below 175 nm (the bandgap of RbCl) the d–f emission is very weak for Ce3+, Pr3+ and Nd3+ doped RbCl and the emission spectra are dominated by defect related emission. This indicates that energy transfer from the host lattice to the fd states is inefficient which prevents application as a scintillator material.