Optical properties of praseodymium concentrated phosphates

The optical properties of Pr3+ ions in cyclotetraphosphates M1PrP4O12 (M1 = Cs, Rb), cyclotriphosphate PrP3O9 · 3H2O and diphosphate NaPrP2O7 have been investigated. Emission spectra under selective laser excitation in the 3PJ multiplets (J = 0, 1, 2) have been measured both at room and low temperatures. The resulting fluorescent emissions originating mainly from the 3P0 level exhibit very fast decay times shorter than 100 ns at 6 K. The results concerning cyclotetraphosphates are compared with those obtained for the corresponding polyphosphates M1Pr(PO3)4 with the aim of understanding the possible role of the cyclic structure. In the same way, the results concerning the hydrated cyclotriphosphates are compared with those obtained for the corresponding anhydrous polyphosphate Pr(PO3)3, in order to point out the role of water molecules. All the materials under consideration (cyclotriphosphate PrP3O9 · 3H2O excepted) exhibit intense ultraviolet emissions under X-ray or VUV synchrotron radiation excitation. These emissions originating from Pr3+ 4f5d → 4f2 transitions have decay times shorter than 10 ns at 6 K. Comparing the obtained room temperature emission spectra under X-ray excitation with the corresponding bismuth germanate Bi4Ge3O12 spectrum measured under the same experimental conditions shows that the phosphates under consideration exhibit significant relative light yields (up to 67% for CsPrP4O12).