Controlled synthesis and luminescence properties of NaLnW 2O 8 nanocrystals

Abstract

Tetragonal phase NaLnW 2O 8 (Ln = Y, Yb, Er, Tm, Eu, Gd, Ho, Ce, and Sm) nanocrystals were successfully prepared via a hydrothermal method. It is found that large ionic radii of lanthanide ions and high reaction temperature are beneficial for the formation of NaLnW 2O 8. The upconversion luminescence properties of NaYW 2O 8:Yb 3+/Er 3+ and NaYW 2O 8:Yb 3+/Tm 3+ were studied under 980 nm excitation. It is found that the luminescence intensity of 2H 11/2 → 4I 15/2 is much stronger than that of 4S 3/2 → 4I 15/2 as well as 4F 9/2 → 4I 15/2 in NaYW 2O 8:Yb 3+/Er 3+. Interestingly, there is no apparent change in the intensity ratio of 2H 11/2/ 4S 3/2 → 4I 15/2 to 4F 9/2 → 4I 15/2 on Er 3+ concentration. By analyzing the Raman spectrum, we suggested that the nonradiative relaxation of 2H 11/2 → 4S 3/2 is inefficient in NaYW 2O 8:Yb 3+/Er 3+, resulting in the strong 2H 11/2 → 4I 15/2 emission. The CIE coordinates of the green luminescence changed with excitation power. While for NaYW 2O 8:Yb 3+/Tm 3+, the CIE coordinates of the blue luminescence (0.14, 0.10) is almost unchanged with excitation power. In addition, the photoluminescence of NaYW 2O 8:Eu 3+ excited at different wavelengths was studied in detail.