Intrinsic and impurity-induced emission bands inSrHfO3

Abstract

To better understand the scintillation mechanism in SrHfO 3-based scintillators we investigate in detail their x-ray excited radioluminescence ͑RL͒ emissions. The Gaussian decomposition of the undoped SrHfO 3 RL spectra manifests the presence of four emission bands peaking at 3.0, 4.0, 4.6, and 5.1 eV. Based on corresponding photoluminescence emission and excitation spectra we tentatively associate the observed bands with excitonic or defect-related emissions. When doped by Ce 3+ or Pb 2+ luminescent activators, the RL spectra feature two or three new bands, respectively. The temperature dependence of all RL spectra demonstrates a competition between activators and intrinsic or defect centers in carrier capture. Around room temperature the emission process is completely dominated by recombination at activator centers. In the case of Pb 2+ activator we also study in detail the concentration dependence of the RL spectra below room temperature exhibiting an optimal value around 0.3 mol %.

SrHfO3-based phosphors and scintillators

“…Ce 3+ emission intensity increases up to Ce0.1 sample. The origin of the 335 nm band is in question as it has not been observed in the stoichiometric undoped SHO [12]. Its spectral position is very close to that of Pb 2+ center [10,11], but contamination by Pb ions is practically excluded in these samples (checked by ICP analysis).…”

“…Very recently the systematic study of the excitation and emission characteristics in the undoped stoichiometric SHO has been performed [12] which reveals quite several UV-VIS emissions ascribed to the exciton and defect centers. In the Pb or Ce-doped SHO the competition between these ''intrinsic'' centers and the dopants was demonstrated.…”

Trapping states and excited state ionization of the Ce3+ activator in the SrHfO3 host

“…Therefore it may be concluded that these peaks follow first order recombination kinetics [12]. The contour plot displayed in Figure 2 shows the presence of a prominent emission due to Ce 3+ ion at around 400 nm [6,13] accompanied by a weak defect emission at higher wavelength.…”

“…On the other hand, in this case the distortion of the temperature dependence of the PL intensity could occur due to the energy losses in the process of transfer between the host and the Ce 3+ center. Nevertheless, PLE spectra of SHO:Ce 3+ measured in the VUV region [13] showed rather efficient energy transfer between the SHO host and the Ce 3+ ion. PLE spectra at RT (see Figure 4) show in great detail that the transfer of excitation from the host to the Ce 3+ luminescence ion is not only efficient but also fast.…”

“…The observation might be due to decreasing efficiency of the energy transfer between the host and the Ce 3+ center with decreasing temperature. This is feasible considering that the Ce 3+ excitation is competing with the excitation of the self-trapped exciton or some other state [13] that is quenched (thermally disintegrated) with increasing temperature. Consequently, for the purpose of defining the correction curve (due to the intracenter Ce 3+ temperature quenching) the PL intensity from RT down to low temperatures was considered constant.…”