Novel quantum cutting (QC) phosphor KYF4:  Tb3+, Yb3+ doped Ag nanoparticles (NPs) was prepared by using the sol-gel method. Plasmon enhanced near-infrared (NIR) QC involving Yb3+ ion at 975 nm (2F5/2→2F7/2) emission was achieved under the excitation of 374 nm (7F6→5D3) and 485 nm (7F6→5D4) of Tb3+ ions, respectively. The effect of Ag NPs on NIR QC luminescence was investigated, and the results show that QC luminescence intensity first increases, then decreases with the increase of the Ag NPs concentration. The maximum enhancement factor is about 1.9 when the concentration of Ag NPs is 0.5%. Our study may have potential application in the field of silicon-based solar cells.

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Tb 4+-Yb 3+ co-doped NaYF 4 nanoparticles (NPs) are prepared by sintering the assynthesized NaYF 4 :Tb 3+ , Yb 3+ NPs at 380°C under air atmosphere. The oxidization of Tb 3+ ions to Tb 4+ ions in NaYF 4 NPs after sintering is demonstrated through X-ray photoelectron spectroscopy (XPS). The near-infrared (NIR) downconversion (DC) luminescence of Tb 4+-Yb 3+ couple is measured and investigated for the first time. The results show that DC luminescence of Tb 4+-Yb 3+ couple enhance obviously compared with Tb 3+-Yb 3+ couple in assynthesized sample. The enhancement factor is about 14 and 19 excited at 379nm and 487nm, respectively. On analyzing the exponential dependence of NIR fluorescence intensity on the pumping power, we reveal that the energy transfer (ET) mechanism from Tb 4+ to Yb 3+ in NaYF 4 NPs occurs by the single-step ET process. Our study may provide a promising DC layer on the top of silicon-based solar cells to improve the photovoltaic conversion efficiency.

Nanoscale quantum cutting (QC) phosphor β-NaYF 4 :Tb 3+ ,Yb 3+ nanoparticles (NPs) and noble metal Ag NPs are synthesized respectively, then β-NaYF 4 :Tb 3+ ,Yb 3+ NPs are doped with Ag NPs uniformly. Experimentally, plasmon enhanced near-infrared (NIR) QC involving a Yb 3+ ion at 977nm (2 F 5/2 → 2 F 7/2) emission is achieved under 377nm (7 F 6 → 5 D 3) excitation of Tb 3+ ions. The QC luminescence intensity first increases, then decreases with the increase of Ag NPs concentration. The maximum QC luminescence enhancement factor reaches 2.4 when the concentration of Ag NPs is 0.25%. Theoretically, a 3D finite-difference time-domain (FDTD) simulation is carried out to numerically estimate the electric field enhancement around Ag NPs, and then the theoretical QC luminescence enhancement factor is calculated. Our study may provide a promising QC layer on the top of silicon-based solar cells to improve the photovoltaic conversion efficiency.