Vacuum ultraviolet spectroscopic analysis of Ce3+-doped hexagonal YPO4·0.8H2O based on exchange charge model

The hexagonal YPO4·0.8H2O:Ce3+ nanophosphors are successfully prepared by the microwave-hydrothermal technique for the first time. The 4f-5d excitation spectrum of Ce3+ ion in the synthesized samples is recorded at 10 K using synchrotron radiation after the crystalline phase structure was confirmed by the X-ray diffraction(XRD) analysis. The combination of the effective Hamiltonian model for 5d1 configuration of Ce3+ ions and the exchange charge model of crystal-field (CF) theory is employed to analyze both the present electronic spectra measured by us and the case of the tetragonal crystalline powder sample of YPO4:Ce3+ reported by van Pieterson et al. (Phys. Rev. B: Condens. Matter. 65 (2002) 045113). The calculated 5d electronic energy levels of Ce3+ ions doped in two crystalline phases are in good agreement with the experimental results. The obtained CF strength parameters for both the cases suggest that Ce3+ ions in the hexagonal phase experience a stronger CF effect. In addition, the expansion technique of CF Hamiltonian along the chosen point-group chain is proposed to qualitatively understand the relationship between the local structure around Ce3+ impurities and the observed 5d energy splitting pattern for two cases.