| The main problem in the solar cell application is the mismatch between the photon distribution in solar spectrum and the response range of the solar cell. The down-conversion (DC) energy transfer process of the rare earth ions could absorb the ultraviolet and visible photon, for which the solar cell could not make sufficient use, and the energy losses can be efficiently reduced by spectrum modification. It could be an inexpensive and efficient way to enhance the photo-electric conversion efficiency. To solve the problems of spectrum modification materials, such as narrow absorption, unable controlled energy transfer process, and low efficiency of DC near-infrared luminescence, we manufactured a series of photonic crystals. With the photonic band gap and plasmon resonance local electric field of Ag nanoparticles, the energy transfer process and the excited radiation efficiency was regulated. By researching on photonic band gap factors on the DC luminescence properties and the influence of the energy transfer mechanism, the spectrum modulation for solar cell photo-electric conversion efficiency enhancement mechanism was’explored.1. The investigation of down-conversion(DC) energy transfer enhancement by photonic band gapThe suppression of spontaneous emission and modifications of photonic mode density could be controlled by the photonic band gap in photonic crystals, and enhance the resonance energy transfer fluorescence between donor and acceptor. In the experiments, by means of tuning the photonic band gap, the spontaneous radiation of donor was suppressed, the down-conversion energy transfer was enhanced, and the near-infrared emission was improved. The main research contents are as follows:In the Ce-Nd codoped YAG inverse opal photonic crystal, the photonic band gap could suppress the spontaneous radiation of Ce3+ at 525 nm. The fluorescence radiative decay results show that the down-conversion energy transfer efficiency was improved from 18.9% to 30.4%, and the intensity of Nd3+ at 1070 nm was enhanced.The Ce-Nd down-conversion energy transfer is a classical stokes down-conversion process. But in the emission of Er3+, excited by 456nm, it is a multiphoton quantum cutting emission process. In the experiments, Ce-Er codoped YAG inverse opal photonic crystal was fabricated. The Ce3+ was choosed to absorb energy in the visible region and improve the bad f-f type transition of Er3+. And with the adjustment of photonic band gap, the energy transfer efficiency was improved from 26.3% to 38.8% and the multiphoton quantum cutting emission of Er3+ was enhanced.2. The investigation of cooperative quantum cutting energy transfer enhancement by photonic band gapIn the cooperative quantum cutting luminescence, the probability of energy decay by cooperative quantum cutting energy transfer process is very low. To solve this problem, we use the photonic band gap to regulate the density of photon states of donor ion and enhance the density of electron on the excited state. It could improve the energy transfer process. The cooperative quantum cutting of Tb-Yb is a classical cooperative quantum cutting luminescence. In the both of Tb-Yb codoped YPO4 inverse opal photonic crystal, the suppression of Tb3+ spontaneous radiation by photonic band gap could also improve the near-infrared emission of Tb-Yb cooperative quantum cutting energy transfer, and the theoretical quantum cutting quantum efficiency was increased from 131.2% to 140.5%. It is different with the f-f type transition of Tb3+that the f-d transition of Ce3+ has a more effective and broad visible emission. The excited Ce3+could excite two Yb3+ to radiate two near-infrared photons. In the Ce-Yb codoped YAG inverse opal photonic crystal, the suppression of Ce3+ spontaneous radiation could also improve Ce-Yb cooperative DC energy transfer, the theoretical quantum cutting quantum efficiency was increased from 122.0% to 131.1%.3. The enhancement of Tb-Yb cooperative quantum cutting excitation efficiency by Ag nanoparticles.The research of the novel property in the physics and chemistry fields makes it possible to improve the emission of rare earth ions by metal nanoparticles. In the experiments, we manufactured NaYF4:Tb, Yb nanoparticles by thermal decomposition method. When the NaYF-t: Tb, Yb nanoparticles were dropped in the 3D structure of photonic crystals, with the suppression of Tb3+ spontaneous radiation by photonic band gap, the Tb-Yb cooperative quantum cutting energy transfer efficiency was increased. After that, the combined action of Ag nanoparticles plasmon resonance local electric field and the photonic band gap in photonic crystal could further improve Tb-Yb cooperative quantum cutting emission. The possible of energy transfer between Ag nanoparticles and rare earth ions was also discussed.In another experiment, the Ag nano film was fabricated on the PS opal photonic crystal by magnetron sputtering. When the NaYF4:Tb,Yb nanoparticles dropped on the Ag nano film, the emission of Tb3+ and Yb3+ was enhanced. The combined action of resonance local electric field of Ag nano film could also improve the Tb-Yb cooperative quantum cutting luminescence, and improve the near-infrared luminescence. When the photonic band gap was accordance with the wavelength of the emission of Tb3+ or Yb3+, the luminescence could be further improved. |
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