89Y MAS NMR in Red Phosphor, Eu-Doped Y2O2S. Assignment of Peaks Shifted by Paramagnetic Eu3+, Spin Lattice Relaxation Time, and Eu Distribution

89Y MAS (Magic angle spinning) NMR has been investigated to study the local environment of Y sites in a red phosphor, Eu doped-Y2O2S (Eu–Y2O2S), with varying the Eu content. Despite the presence of paramagnetic Eu3+ ions, high resolution spectra were acquired and a number of local environments were detected. The assignment of the resonances to different Y local environments was made on the basis of signal intensities, chemical shifts, and spin-lattice relaxation times (T1) in conjugation with the crystal structural data which were obtained by the Rietveld method. Besides the main peak in pure Y2O2S, four peaks caused by the –Eu species and ten peaks caused by the Eu––Eu species were distinguished in Eu–Y2O2S, where Y1 is the next nearest-neighbor Y site for the doped Eu atom, and –Eu and Eu––Eu are substituted by one and two Eu, respectively. Y atoms (Y2, Y3, ··· Yn), which are further from the second and more nearest-neighbors from Eu were observed at the same resonance position for all samples investigated with that of pure Y2O2S. The T1 values of the 89Y signal were reduced from 6.6 h for pure Y2O2S to 230 s (10 mol% Eu–Y2O2S) for Yn (n ≥ 2), to several tens of seconds for Y1–Eu and to several seconds for Eu–Y1–Eu in Eu–Y2O2S. The Eu content to Y in the region where Eu atoms are randomly isolated was estimated from the intensity ratio of the total intensities of the four Y1 peaks to the main peak. T1 reduction and a line-broadening due to paramagnetic Eu3+ ions are discussed in relation to the distribution of Eu ions.