利用同步輻射光源探討量子剪裁磷酸鹽螢光體之發光特性與機制

Abstract

量子剪裁泛指螢光體每吸收一個真空紫外光子後，可以將其能量轉換成兩個或兩個以上的可見光子放出；一般真空紫外可激發螢光粉主要應用於電漿顯示面板與無汞照明裝置。理論上，透過量子剪裁的過程有機會能夠讓量子效率達成200％；為了能實現此目標，選擇適當的螢光材料便顯得非常重要。根據文獻的記載，摻雜稀土離子的氟化物是最適合發展真空紫外激發裝置的相關應用；然而氟化物在大氣下的化學穩定性很低，相較之下，氧化物具有優秀的化學穩定性，而且合成上較氟化物簡易，因此，氧化物便成為另一項適合探討量子剪裁效應的選擇。 本文中，我們利用同步輻射光源探討了Ba3Gd(PO4)3、Sr3Gd(PO4)3與Ca8MgGd(PO4)7等磷酸鹽量子剪裁螢光體；並且利用螢光放射與螢光激發光譜等量測實驗建立Tb3+- Tb3+及Gd3+- Tb3+的能量轉移機制與量子剪裁模型。

Quantum cutting (QC) is a concept that the energy of a vacuum ultraviolet (VUV) photon is more than twice the energy of a visible photon, so that there is enough energy to emit more than one visible photon per each VUV photon absorbed. The application of VUV-excited phosphors are mainly focus on plasma display panels (PDP) and mercury-free lighting devices. Theorolly, it is possible to achive quantum efficiency (QE) as high as 200% through a QC process. To fulfill the requirement of QC, it is importment to choice the proper phosphor materials. According to several studies, rare earth ion-doped fluoride materials can be an outstanding canadle for developing the application of VUV-excited sources. However, the chemical properties of fluoride materials are unstable under atmosphere, in contrast, oxide have good chemical stability, and easily to be synthesized than fluorides. In a sense, oxide could be another choice suitable for quantum cutting effect. In this work, by using synchrotron radiation as a light source, we have investigated several phosphate quantum-cutting phosphors, such as Ba3Gd(PO4)3, Sr3Gd(PO4)3, Ca8MgGd(PO4)7. Based on the analysis of the experimental photoluminescence (PL), photoluminescence excitation(PLE), We have also proposed plausible mechanisms and energy level diagrams involving Tb3+- Tb3+or Gd3+- Tb3+energy transfer model to rationalize the observed QC process.