Broadband spectral conversion of visible light to near-infrared emission via energy transfer from Ce 3+ to Nd 3+ /Yb 3+
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Xiaofeng Liu State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Zhijun Ma State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
Jianrong Qiua) State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China; and Institute of Optical Communication Materials, South China University of Technology, Guangzhou 510640, China (Received 27 April 2010; accepted 19 November 2010)
Broadband spectral conversion from visible light to near-infrared radiation in Ce3+–Nd3+/Yb3+ codoped yttrium aluminum garnet is reported. Excitation, emission spectra, and decay curves have been measured to prove the energy transfer from Ce3+ to Nd3+ or Yb3+. The energy transfer efficiencies have been estimated, and the mechanisms of the energy transfer between Ce3+ and Nd3+/Yb3+ have been proposed. Ce3+–Nd3+ codoped YAG can obtain more effective emission in the desired near-infrared region (around 1100 nm) through broadband conversion, showing potential application to improve the conversion efficiency of Si solar cells.
I. INTRODUCTION
Photoelectric transformation efficiency of solar cells can be improved by spectral modification, which reduces the energy losses that limit the efficiency related to spectral mismatch.1 There are two ways to adapt the solar spectrum before it is absorbed by the solar cells. One is known as upconversion (UC), whereby two lower-energy photons are absorbed to give out one higher-energy photon. It is a nonlinear process depending on the incident power and is especially useful for solar cells with a large band gap where transmission losses dominate. The other is to cut one higher-energy photon into two lower-energy photons, known as downconversion (DC). This is a linear process and is most beneficial for solar cells with a smaller band gap where thermalization losses are the major loss factor. Using nonconcentrated sunlight as light source, DC has the capability to get high conversion efficiency. For DC spectral modification method by rare earth (RE) doping, a RE ion pair is usually needed. One ion acts as a sensitizer to absorb higher-energy photons and the other as luminescence center to output lower-energy photons. To consider the practical application on solar cells, Ce3+ is chosen as sensitizer, which shows broadband absorption due to the f–d transition in high-energy region. For c-Si solar cell, the spectral response is gradually a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.84 J. Mater. Res., Vol. 26, No. 5, Mar 14, 2011
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increased from the ultraviolet (UV) region to the nearinfrared (NIR) region with the maximum value at around 1100 nm, which is in agreement with the band gap of Si (1.1 eV). Many investigations have been carried out on DC of UV or visible photons to NIR photons choosing Yb3+ as the luminescence center22–6 because the energy 3+ 2 level difference o
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