| Recently, rare earths doped near infrared (NIR) down-conversion (DC) luminescent materials have attracted great attention of researchers, due to the enormous potential application in silicon based solar cells. Over the past decade, researchers have focused on the development of a highly efficient system of rare earth ions with NIR DC emission. Because the luminescence process of these systems is much related to the phonon energy and the structure of the matrix, so the matrix materials which have excellent performance have developed as well. However, even in a suitable matrix, the emission efficiency is relative low because of their special f-f electronic transition which result in low excitation efficiency. Moreover, high energy loss of non-radiative transition and spontaneous radiation of the donor ion which lead to low energy transfer (ET) efficiency. These factors seriously limits it’s practical application in Si solar cells. It is a key problem to improve the ET efficiency and the excitation efficiency of the rare earth ions. According to the previous research, it is found that by coupling of metal nanoparticle (NPs) surface plasmons with photonic crystal effect, the emission properties of these systems may be considerably improved. Therefore, the luminescence properties and mechanism of the rare earths doped DC photonic crystal materials with gold or silver NPs have been studied in this paper.Four classic NIR DC system:YPO4:Tm3+, Yb3+/YPO4:Tb3+, Yb3+/SiO2:Tb3+, Yb3+/ Y3Al5O12:Ce3+, Yb3+ are chosed to study the effect of the photonic band gap (PBG) of the inverse opal. Those four DC system inverse opal photonic crystals are synthesized by colloidal crystal templates method via sol-gel method. Experimental results show that the spontaneous radiative transitions of donor ions are suppressed when the photonic band gap overlap emission band of the donor ions. On the contrary, the NIR emission intensity of the Yb3+is effectively enhanced, when the PBG position keep away from the emission band of donor ions, PBG have no impact on the luminescence property of RE3+-Yb3+.In the SiO2: Tb, Yb inverse opals, by introduction of Ag+, the Ag NPs and their clusters are obtained through the sintering process. It is found that the Ag NPs lead to a significant enhancement in spontaneous emission of Tb3+ and the NIR emission of Yb3+. Meanwhile, different kinds of Ag aggregates can be efficiently sensitizing Tb3+ or Yb3+. In particular, the NIR emission of Yb3+have significant improved due to the intense and wide band excitation peak of 200-500 nm of Ag aggregates.In the Y3AlsO12:Ce3+, Yb3+ inverse opals, by coating with SiO2 shell, the surface defects of inverse opal photonic crystals are modified. Meanwhile, the formation of SiO2 shell may reduce the reflection of the excitation light source. This two reasons lead to the greatly enhancement of the visible-NIR emission of Ce3+-Yb3+. In addition, through the introduction of Au NPs into SiO2 shell, the absorption of Ce3+ is increased due to the surface plasmon resonance (SPR) effect of Au NPs. At the same time, the maximum reflection effect of Au on infrared light can reduce the reuptake of NIR emission. These two kinds of effect lead to achieve further strengthening of the visible-NIR luminescence. |
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