Spectroscopic investigations of neodymium cyclotriphosphates

In the framework of systematic investigations in the properties of rare-earth cyclotriphosphates, polycristalline samples of La_1−xNd_xP₃O₉·3H₂O have been synthesized with x=5×10⁻³, 10⁻², 5×10⁻², 10⁻¹ and 1. Absorbance spectra were measured at 300 K in the 300-1000 nm region. Fluorescent emissions from the ⁴F_3/2 multiplet were observed at 300 and 6 K under pulsed laser excitations in either the ⁴F_7/2 or ⁴F_3/2 multiplet and the decays of these emissions were measured. These decays are exponential with decay-times on the order of 100 ns for all values of x. No important lengthening is observed as either the Nd concentration is decreased from 100 to 0.5 at% or the temperature is lowered from 300 to 6 K. These results are in contradiction with those obtained for the anhydrous La_1−xNd_x(PO₃)₃ compounds prepared by progressively heating the corresponding La_1−xNd_xP₃O₉·3H₂O powder materials, a fact which shows the predominant role played by the water molecules in the Nd³⁺ luminescence in the considered hydrated compounds.