Zhuohong Feng

Plasmon enhanced near-infrared quantum cutting of KYF 4 : Tb 3+ , Yb 3+ doped with Ag nanoparticles

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.

Plasmon enhanced near-infrared quantum cutting and simulation analysis of β-NaYF 4 :Tb 3+ , Yb 3+ doped with Ag nanoparticles

Nanoscale quantum cutting (QC) phosphor β-NaYF4:Tb3+,Yb3+ nanoparticles (NPs) and noble metal Ag NPs are synthesized respectively, then β-NaYF4:Tb3+,Yb3+ NPs are doped with Ag NPs uniformly. Experimentally, plasmon enhanced near-infrared (NIR) QC involving a Yb3+ ion at 977nm (2F5/2→2F7/2) emission is achieved under 377nm (7F6→5D3) excitation of Tb3+ 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.

Efficient near-infrared downconversion and energy transfer mechanism in Tb 4+ -Yb 3+ co-doped NaYF 4 nanoparticles

Tb4+-Yb3+ co-doped NaYF4 nanoparticles (NPs) are prepared by sintering the as-synthesized NaYF4:Tb3+, Yb3+ NPs at 380°C under air atmosphere. The oxidization of Tb3+ ions to Tb4+ ions in NaYF4 NPs after sintering is demonstrated through X-ray photoelectron spectroscopy (XPS). The near-infrared (NIR) downconversion (DC) luminescence of Tb4+-Yb3+ couple is measured and investigated for the first time. The results show that DC luminescence of Tb4+-Yb3+ couple enhance obviously compared with Tb3+-Yb3+ couple in as-synthesized 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 Tb4+ to Yb3+ in NaYF4 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.

Luminescence properties of alkali metal ions sensitized CaFCl:Tb3+ nanophosphors

A series of CaFCl:Tb3+ and CaFCl:Tb3+,A+ (A=Li, Na and K) nanophosphors were synthesized by the one-step sol-gel method, which were reported for the first time. The sample consisted of monodisperse particles, the average size of which was 37 nm. The emissions of Tb3+ ions and oxygen defects OF? were demonstrated in the CaFCl:Tb3+ samples. The former was made up of several peaks at 488, 545, 587 and 623 nm, ascribed to 5D4→7FJ (J=6−3) transitions of Tb3+ ions. The latter was shown as a broad band peaked at about 450 nm. Alkali metal ions A+ (A=Li, Na and K) were introduced as the charge compensators to improve the luminescence of samples. The influence of charge compensators on the emissions of Tb3+ ions and oxygen defects OF? was investigated by the measurement of fluorescence spectra and luminescence decay curves. The results indicated that all the charge compensators weakened the defects emission. Furthermore, Li+ ion was the best charge compensator, because it not only reduced the defects emission but also increased the emission intensity of Tb3+ significantly. Our results suggested that this nanophosphor sensitized by the charge compensator might broaden potential applications of rare-earth doped CaFCl.

Temperature investigation of frequency upconversion in Er 3+ /Yb 3+ -codoped PLZT electro-optic ceramic

The upconversion fluorescence spectra of Er3+/Yb3+: PLZT exciting at 980 nm were measured from 10K to 320K. A model for the dynamics of frequency upconversion processes was proposed. Based on the model, the upconversion luminescence intensities curves as a function of temperature were fitted and the temperature characteristics of upconversion luminescence were discussed.

Analysis of the dynamics of frequency upconversion in Er(su3+}/Yb(su3+} co-doped KY(WO 4 ) 2 crystal

The absorption spectra and the luminescence decay curve of Er³⁺/Yb³⁺ co-doped KY(WO<inf>4</inf>)<inf>2</inf> crystal was measured. The radiative transition rates were calculated by Judd-Ofelt theory. The Yb-to-Er energy-transfer rate and the cooperative upconversion coefficients were estimated by numerically solving the rate equations and fitting simulated curve to the measured data.