Near-infrared Quantum Cutting Enhancement By Localized Surface Plasmons

Near-infrared(NIR)quantum cutting(QC)can improve the photovoltaic conversion efficiency of solar cells by means of spectrum modulation.However,most of NIR QC materials have low quantum efficiency,which will reduce the photovoltaic conversion efficiency.To solve this problem,micron-scale and nano-scale rare-earth(RE)ions doped fluoride materials are prepared,respectively,and their NIR QC luminescence are investigated.More importantly,plasmon-enhanced NIR QC luminescence is realized by the localized surface plasmons(LSPs)of noble metal nanoparticles(NPs).Furthermore,the rate equation of NIR QC luminescence is established and the dynamic process of NIR QC luminescence is analyzed.The research contents are as follows:1.(a)KYF4:Tb3+,Yb3+ microparticles and NaYF4:Tb3+,Yb3+ NPs are prepared by sol-gel method and coprecipitation method,respectively.The excitation and emission spectra are measured,and the results show that the optimal doping concentrations of Tb3+ion and Yb3+ ion are 15%and 10%,respectively.The NIR QC luminescence of KYF4:Tb3+,Yb3+ microparticles and NaYF4:Tb3+,Yb3+ NPs under high Tb3+ ion doping concentration are realized.The energy transfer(ET)mechanism between Tb3+-Yb3+ ion pairs in the NIR QC luminescence process is proved to be cooperative ET.(b)NaYF4:Tb4+,Yb3+ NPs are prepared by sintering the as-synthesized NaYF4:Tb3+,Yb3+ NPs at high temperature.The NIR downconversion(DC)luminescence of NaYF4:Tb4+,Yb3+ NPs is investigated,and the results show that NIR DC luminescence of Tb4+-Yb3+ ion pairs enhances obviously compared with Tb3+-Yb3+ ion pairs.The NIR DC luminescence enhancement factor is about 14 and 19 excited at 379 nm and 487 nm,respectively.The ET mechanism between Tb4+-Yb3+ ion pairs in the NIR DC luminescence process is proved to be single-step ET.2.(a)Ag NPs are synthesized by chemical reduction method.Then,KYF4:Tb3+,Yb3+microparticles and NaYF4:Tb3+,Yb3+ NPs are doped with Ag NPs.Plasmon-enhanced NIR QC luminescence of KYF4:Tb3+,Yb3+ microparticles and NaYF4:Tb3+,Yb3+NPs are obtained by the LSPs of Ag NPs.The effect of Ag NPs on NIR QC luminescence is investigated.The optimal concentration of Ag NPs is 0.5%with the maximum NIR QC luminescence enhancement factor about 1.6(?ex = 374 nm)and 1.9(?ex = 485 nm)in KYF4:Tb3+,Yb3+ microparticles,and the optimal concentration of Ag NPs is 0.25%with the maximum NIR QC luminescence enhancement factor about 2.4(?ex = 377 nm)in NaYF4:Tb3+,Yb3+ NPs.The electric field distribution around Ag NPs is simulated by finitie-difference time-domain(FDTD)method,and the NIR QC luminescence enhancement mechanism is analyzed:the LSPs resonance peak of Ag NPs matches with the excitation peak of Tb3+ ion,which will enhance the excitation efficiency of Tb3+ ion.(b)Au nanorods(NRs)are synthesized by seed-mediated method.Then,NaYF4:Tb3+,Yb3+ NPs are doped with Au NRs.Plasmon-enhanced NIR QC luminescence of NaYF4:Tb3+,Yb3+ NPs is obtained by the LSPs of Au NRs.The influence of Au NRs on NIR QC luminescence is investigated,and the results show that the optimal concentration of Au NRs is 0.12%with the maximum NIR QC luminescence enhancement factor about 3.The electric field distribution around Au NRs is simulated by FDTD method,and the NIR QC luminescence enhancement mechanism is analyzed:the LSPs resonance peak of Au NRs matches well with the emission peak of Yb3+ ion,which will improve the radiative transition rate of Yb3+ ion.3.NaYF4:Er3+ NPs is prepared by coprecipitation method.The excitation and emission spectra are measured,and the results show that the optimal doping concentration of Er3+ ion is 4%.The three-photon NIR QC luminescence at 1520 nm of NaYF4:Er3+ NPs is obtained under the excitation of 519 nm.Through the decay curves of Er3+,ion,the ET mechanism between Er3+ ions is proved to be two-step cross-relaxation ET.More importantly,Ag nanocubes(NCs)are synthesized by chemical reduction method.Then,NaYF4:Er3+ NPs are doped with Ag NCs.Plasmon-enhanced three-photon NIR QC luminescence of NaYF4:Er3+ NPs is realized by the LSPs of Ag NCs.The influence of Ag NCs on three-photon NIR QC luminescence is investigated,and the results show that the optimal concentration of Ag NCs is 0.10%with the maximum three-photon NIR QC luminescence enhancement factor about 2.86.The electric field distribution around Ag NCs is simulated by FDTD method,and three-photon NIR QC luminescence enhancement mechanism is analyzed:the LSPs resonance peak of Ag NCs matches well with the excitation peak of Er3+ ion,which will enhance the excitation efficiency of Er3+ ion.4.Based on Judd-Ofelt(J-O)theory,and combined with emission spectrum or absorbance spectrum of Tb3+ ion and Er3+ ion,the J-O intensity parameters of Tb3+ ion or Er3+ ion in KYF4:Tb3+,Yb3+ microparticles,NaYF4:Tb3+,Yb3+ NPs and NaYF4:Er3+ NPs are calculated,respectively.Then,various radiative parameters,such as radiation transition probability,nonradiation transition probability,cross-relaxation rate and ET rate,are calculated through J-O intensity parameters.Subsequently,the rate equation of NIR QC luminescence is established,the dynamic process of NIR QC luminescence is analyzed and the theoretical QC efficiency is calculated.