Rare-earth free sensitizer in NaLuCrF₄:Er upconversion material

Bui The Huy^1,2，Zayakhuu Gerelkhuu²，The-Long Phan³，Ngo Tran³，Yong-IllLee²

1. Institute of Research and Development, Duy Tan University2. Department of Chemistry, Changwon National University3. Department of Physics, Hankuk University of Foreign Studies

摘 要：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_xF4 Er_0.02（x = 0-0.9）upconversion material by substituting Lu³⁺ ions with Cr³⁺in the absence of Gd³⁺. The change in upconversion luminescence intensity appears with saddle-like shape. We suggest that Cr³⁺ 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 Cr³⁺ and Er³⁺ ions and Cr-Er 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 Cr³⁺ contents, and to the coupling between Cr³⁺ and/or Er³⁺ ions for the case of high Cr³⁺contents. Magnetization and electron-spin-resonant measurements were performed to understand the correlation between the optical and magnetic properties.

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