VUV spectroscopy of double phosphates doped with rare earth ions

Structure and optical properties of Eu3+ and Gd3+ in sodium double phosphates were studied. Emission spectra were measured under VUV/UV excitation at room and low temperatures. Structural differences in various kinds of sodium double phosphate matrices are manifested in their optical behaviors. Under synchrotron radiation, Na3Gd(PO4)2 exhibits the ultraviolet 6PJ → 8S7/2 and red from the 6GJ level emissions. In the case of europium and gadolinium systems, the Gd3+ → Eu3+ energy transfer process was observed and investigated. Absence of emission from the 5DJ and 6IJ levels of the Gd3+ ion and from higher 5DJ states of Eu3+ ion was attributed to the effective multiphonon relaxation which involves only two high-energy phonons of the phosphate group in this lattice.