LaPO4:Ce3+ and LaPO4:Ce3+, Tb3+ phosphor layers have been deposited successfully on monodispersed and spherical SiO2 particles of different sizes (300, 500, 900 and 1200 nm) through a sol–gel process, resulting in the formation of core–shell structured SiO2@LaPO4:Ce3+/Tb3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microcopy (SEM), transmission electron microscopy (TEM), and general and time-resolved photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting SiO2@LaPO4:Ce3+/Tb3+ samples. The XRD results demonstrate that the LaPO4:Ce3+, Tb3+ layers begin to crystallize on the SiO2 templates after annealing at 700 °C, and the crystallinity increases on raising the annealing temperature. The obtained core–shell phosphors have perfectly spherical shape with a narrow size distribution, non-agglomeration, and a smooth surface. The doped rare-earth ions show their characteristic emission in the core–shell phosphors, i.e. Ce3+ 5d–4f and Tb3+ 5D4–7FJ (J = 6–3) transitions, respectively. The PL intensity of the Tb3+ increased on increasing the annealing temperature and the SiO2 core particle size. The energy transfer process from Ce3+ to Tb3+ in SiO2@LaPO4:Ce3+, Tb3+ core–shell particles was studied using the time-resolved emission spectra.

To investigate the hot electrons in highly charged electron cyclotron resonance (ECR) plasma, Bremsstrahlung radiations were measured on two ECR ion sources at the Institute of Modern Physics. Used as a comparative index of the mean energy of the hot electrons, a spectral temperature, T spe , is derived through a linear fitting of the spectra in a semi-logarithmic representation. The influences of the external source parameters, especially the magnetic configuration, on the hot electrons are studied systematically. This study has experimentally demonstrated the importance of high microwave frequency and high magnetic field in the electron resonance heating to produce a high density of hot electrons, which is consistent with the empirical ECR scaling laws. The experimental results have again shown that a good compromise is needed between the ion extraction and the plasma confinement for an efficient production of highly charged ion beams. In addition, this investigation has shown that the correlation between the mean energy of the hot electrons and the magnetic field gradient at the ECR is well in agreement with the theoretical models.