上轉換（Up-conversion）是將帶有低能量光子轉換為較高能量光子的光致發光過程，該過程在諸如生物成像、轉換太陽能光譜和安全編碼等許多不同領域具有許多的潛在用途，如今，關於上轉換的研究主要集中在生物醫學信號的偵測和奈米粒子的合成上。於本研究中，本團隊嘗試使用低溫(200℃)、高反應時間(24h)之水熱法，在合成擁有上轉換能力之螢光粉體之鈉釔氟礦(NaYF4)摻雜鐿離子(Yb3+)、銩離子(Tm3+)，並在一系列不同pH值條件下進行NaYF4材料的合成，透過影響其反應機構來控制其形貌，進一步改變其發光強度。結果得知低pH值的樣品比較高pH值的樣品具有更好發光強度，由光譜可看出pH值為4的樣品其450 nm的放光強度大約為pH值為10樣品的67倍之多。另外，我們觀察摻雜Li +的NaYF4樣品，發現稀土離子周圍的局部對稱性失序的作用是由Li+摻雜引起的。於結果中能看出摻雜較高濃度的Li+的NaYF4材料與其對應的無摻雜Li+那組相比具有較強的螢光特性和強度，NaYF4：Yb3+.Tm3+材料摻雜20％ Li+在藍色475 nm發光強度和450 nm發光強度分別為增強3和7倍，而在345 nm和360 nm附近的紫色放光強度分別為約6和9倍。從研究結果中表明，NaYF4：Yb3+ .Tm3+的上轉換發光能力確實大幅提升，具有Li+摻雜的NaYF4材料十分具有潛在的應用性，在增進太陽能電池效率、細胞追蹤偵測甚至於提升植物的光合作用產能的研究領域中都有在未來值得嘗試的機會。

Up-conversion, a photoluminescence process which converts few low energy photons to a higher energy photons, has more potential usages in many different fields like bio-imaging, solar spectrum tuning, and security encoding. Nowadays, researches about up-conversion mainly concentrating on synthesis of nanoparticles to improve inefficient situation for viable implementation. In this Perspective, we use the low temperature of the hydrothermal method in the synthesis process successfully. The morphology of NaYF4 is controlled by the reaction mechanism under series of pH value condition, and the luminescence intensity is further changed. As a result, we observe a sample with a low pH value had a better luminous intensity than a sample with a higher pH value. In addition, we describe that the local symmetry disorder around the rare-earth ions was caused by Li+ doping in host lattice. Local symmetry disorder is the reason for enhancement of photoluminescence. NaYF4 material doped with higher concentration of Li+ has stronger photoluminescence properties and intensity than its corresponding un-doped Li+ group. The NaYF4 absorb the infrared light into the blue-violet luminescence, so that the energy absorption of the aquatic is increased to enhance photosynthesis effect and reach the green energy application.

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