Crystal structure, morphology and optical properties of orange red emitting (Y1–xLnx)2Ti2O7 (Ln = Eu, Sm) solid solutions

Abstract

The present work reports a comparative study of two phosphors families; (Y1-xEux)2Ti2O7 and (Y1-xSmx)2Ti2O7 with (0 ≤ x ≤ 1), prepared by solid-state reaction. XRD, SEM, and Raman spectroscopy combined characterization confirms the phase structure, morphology and purity of the prepared phosphors. XRD analysis had revealed the formation of solid solutions with cubic pyrochlore structure with the space group Fd3m. Rietveld refinement of the XRD data shows that the substitution of Y3+ ion with rare earth ions (Ln3+), having larger ionic radii, causes a systematic increase in the lattice parameter a with the value of x, in (Y1-xLnx)2Ti2O7. Characteristic vibration modes (A1g + Eg + 3F2g) for pyrochlore structure are evidenced using Raman spectroscopy. A clear variation of peak positions was observed for Eg and A1g modes with Ln3+ substitution. The great ability of the host matrix, Y2Ti2O7, for chemical substitution, with lanthanide ions, gives rise to new emitting phosphors. The effect of rare earth Ln3+ concentration on the luminescence performance of the (Y1-xLnx)2Ti2O7 phosphors was studied, by photoluminescence (PL) spectroscopy, and discussed in details. The most intense Eu3+ red emission was obtained with a substitution ratio x = 0.25, while the strongest Sm3+ orange-reddish emission was observed for a ratio x = 0.05. These results prove that the prepared phosphors are promising for applications in solid-state white light emitting diodes (W-LEDs) and orange-red emitting components.