Optical properties of praseodymium concentrated phosphates

Abstract The optical properties of Pr 3+ ions in cyclotetraphosphates M 1 PrP 4 O 12 (M 1  = Cs, Rb), cyclotriphosphate PrP 3 O 9  · 3H 2 O and diphosphate NaPrP 2 O 7 have been investigated. Emission spectra under selective laser excitation in the 3 P J multiplets ( J  = 0, 1, 2) have been measured both at room and low temperatures. The resulting fluorescent emissions originating mainly from the 3 P 0 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 M 1 Pr(PO 3 ) 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(PO 3 ) 3 , in order to point out the role of water molecules. All the materials under consideration (cyclotriphosphate PrP 3 O 9  · 3H 2 O excepted) exhibit intense ultraviolet emissions under X-ray or VUV synchrotron radiation excitation. These emissions originating from Pr 3+ 4f5d → 4f 2 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 Bi 4 Ge 3 O 12 spectrum measured under the same experimental conditions shows that the phosphates under consideration exhibit significant relative light yields (up to 67% for CsPrP 4 O 12 ).