利用無稀土元素製作高效率發光材料及應用

Abstract

現今白光LED之螢光粉多採用稀土元素製作，但稀土元素的提煉及使用對於環境及人類有非常多的隱憂。有鑑於此，在現今綠色環保意識抬頭的世代，使用非稀土元素製作高效率之發光材料，就成為現今許多人研究的目標。 於第一部分，我們提出以不含稀土元素及鎘元素之ZnSe:Mn量子點，搭配藍光LED製作白光照明。為了能配合現今商用藍光LED的激發波長，我們成功克服量子侷限效應將ZnSe:Mn之吸收優化至450 nm以上，並以Mn分裂能階激發出590 nm之橘黃光，搭配藍光LED合成出對於人眼較有益之暖白光。其目前量測出最高量子效率為21%，推估在生物或螢光標記較有應用之機會。 為了製作出應用於照明之高效率螢光粉，我們在第二部分提出新的製程設計，利用現今製作成熟之有機染料C545T、DCJTB及Rubrene，將各種染料溶入各自適當之溶劑後，使染料溶液可在藍光波段有強吸收，且能有效將藍光分別轉換出綠色、黃色、橘色及紅色激發光。我們藉由將高分子聚合物PVP溶入染料溶液中，利用PVP之包覆特性，可有效將染料分子包覆，並使其在乾燥後保留其在溶液態之極性，透過真空加熱後能將染料溶液成粉塊狀，將粉塊研磨後即可得到各種顏色之螢光粉。我們所製作出之綠色、黃色、橘色及紅色螢光粉，可分別在藍光激發下，達到85.4%、89.1%、72.3% 及80.1% 之高轉換效率。將各種粉以適當比例混合後，我們利用綠粉及紅粉合成出非常接近自然白光品質之白光，色溫為5190K及CRI 88，若再加入橘粉可把CRI提升至90以上。 另外，我們將C545T及PVP溶入乙醇後得到之高效率綠光溶液，旋塗成為薄膜態，可在藍光影像激發下顯示明顯綠色的影像，目前之結果可應用在抬頭顯示器薄膜的部分。相對於傳統反射式的顯示薄膜，我們具有高穿透、高亮度及不會有干涉影像，且因傳統式薄膜需要有特定反射角才能看清楚影像之缺點，由於我們薄膜是吸收再放光式，在我們薄膜就不會有視場角問題發生。我們薄膜可吸收藍光轉換為對於人眼較靈敏之綠光，對於顯示基本資訊很有幫助。在實際車上測試後，我們的薄膜確實能得到相對於現今傳統反射式薄膜之效果。 本研究之成果，可有效將藍光轉換為可見光，且能達到高轉換效率，有著極大的潛力取代現今稀土元素之螢光粉，且將我們所製作之螢光溶液製作成薄膜後，應用於抬頭顯示器有著許多優勢。本研究之結果對於現今發光照明及抬頭顯示薄膜都極具開發潛力及實際應用之價值。

Rare-earth mining associated with high messy and polluting business has caused a heavy burden on the environment, so the tremendous harm by using rare-earth elements to produce white LEDs has caught increasing concerns. Therefore, exploring the luminescent material based on non-rare-earth elements has attracted much attention nowadays. Accordingly, we propose a method based on ZnSe:Mn nanoparticles with non-rare-earth and non-cadmium elements in the first part. In order to act with the commercial blue LED, we successfully enhance the optimal excitation wavelength of the ZnSe:Mn nanoparticles above 450 nm. In addition, by doping Mn2+ in ZnSe nanoparticles, electrons in the ZnSe conduction band can be transferred to the Mn2+ energy level effectively and emit orange light at about 590 nm. In our results, ZnSe:Mn nanoparticles can produces a warm white light for human eyes with the excitation of blue light, but the highest quantum efficiency is only 21 %, which is probably better for applications in biomarkers or fluorescent markers than for display or lighting. In order to improve the quantum efficiency, we propose another avenue based on organic dyes, C545T, DCJTB and Rubrene with aqueous solution process in the second part. We use C545T, DCJTB and Rubrene dissolving in respective suitable solvents to produce bright green, yellow, orange and red light effectively by excited blue light. Moreover, by adding PVP to dissolve above dye solutions can simplify the drying process and maintain the optical characteristics after the solvents evaporate. The highest quantum efficiency of green, green, yellow, orange and red phosphor can reach 85.4%、89.1%、72.3% and 80.1%, respectively. In the third part, we focus on producing white light that possesses high CRI and low color temperature. In our experiments, using appropriate proportion of C545T and DCJTB can make our quality of white light close to natural white light, CCT 5190 K and CRI 88 can be reached, using three kinds of phosphors can enhance CRI to reach above 90. Furthermore, we use solution of C545T and PVP to manufacture films of the head up display films by spin coating. Our films do not belong to traditional reflective films. They are for photoluminescence, so compared to the traditional films, our films exhibit many advantages, high penetration, good brightness to human eyes, without image interference from reflection and full field of view. It is expected that the innovative approaches for white-LED lighting and head up display have considerable potential and application value.