13.
Upconversion phosphors are known as a material system that can convert near-infrared light into visible/ultraviolet emissions by sequentially absorbing multiple photons. The studies on upconversion materials often use two rare earth (RE) ions as a sensitizer-activator pair. We investigated the influences on luminescence intensity depending on Cr-doping content (
x) of hexagonal NaLu
0.98–xCr
xF
4Er
0.02 (
x = 0–0.9) upconversion material by substituting Lu
3+ ions with Cr
3+in the absence of Gd
3+. The change in upconversion luminescence intensity appears with saddle-like shape. We suggest that Cr
3+ ions play the dual role as a constituent in host lattice and a sensitizer in the upconversion process. Optimal conditions for gaining the strongest upconversion emission correspond to
x = 0.3–0.5, where there are effective energy transfers between Cr
3+ and Er
3+ ions and CrEr dimers. Apart from these values, the emission intensity decreases rapidly which can be ascribed to the absence of multiple-photon absorption for the case of low Cr
3+ contents, and to the coupling between Cr
3+ and/or Er
3+ ions for the case of high Cr
3+ contents. Magnetization and electron-spin-resonant measurements were performed to understand the correlation between the optical and magnetic properties.
相似文献