Multi-photon Near-infrared Quantum Cutting Enhancement Of NaBaPO₄:Er³⁺ Systems

Due to the ongoing problems of energy crisis and environmental pollution,solar engrgy which is renewable and clean has been attracted wide attention.Photovoltaic power gengration using solar cells is one of the important ways to utilize solar energy.However,the photovoltaic efficiency of solar cells is not efficient because of the spectral mismatch.Multi-photon near-infrared(NIR)quantum cutting(QC)is helpful to improve the photoelectric conversion efficiency of solar cells.NaBaPO₄:Er³⁺phosphor systems are prepared,and the multi-photon NIR QC luminescence properties and the NIR emission enhancement are investigated.The research contents are listed as follows:1.NaBaPO₄:Er³⁺phosphor systems are prepared by the solid-state reaction and the multi-photon NIR QC luminescence properties of samples are investigated.(a)The excitation and emission spectra of NaBaPO₄:Er³⁺phosphors are measured and analyzed.Four-photon NIR QC emission of NaBaPO₄:Er³⁺phosphor has been realized under the377 nm ultraviolet light excitation.The QC mechanism is analyzed by the decay curves,and the QC efficiency is calculated.Moreover,three-photon QC mechanism of NaBaPO₄:Er³⁺under the 485 nm/519 nm excitation has been analyzed,respectively.(b)The excitation and emission spectra of NaBaPO₄:Eu²⁺,Er³⁺phosphors are measured and analyzed,and the three-photon broad-band NIR QC emission is realized in NaBaPO₄:Eu²⁺,Er³⁺phosphor(?_ex=352 nm).The broad-band NIR QC mechanism is analyzed by the decay curves,and the QC efficiency is calculated.2.Plasmon-enhanced NIR QC luminescence of NaBaPO₄:Er³⁺phosphor systems decorated with Ag nano-particles(NPs)is obtained.(a)Ag NPs(including Ag ball NPs and Ag cube NPs)are prepared by chemical reduction method.The relationships between multi-photon NIR emission intensity of NaBaPO₄:Er³⁺and the concentration of Ag NPs(including Ag ball and Ag cube)are investigated.The results show that four-photon NIR emission intensity reaches maximum when the doping concentration of Ag ball NPs is0.3%,and the corresponding enhancement factor is about 1.4(?_ex=377 nm).Three-photon NIR emission intensity reaches maximum when the doping concentration of Ag ball NPs is 0.35%,and the corresponding enhancement factor is about 1.7(?_ex=485nm).Three-photon NIR emission intensity reaches maximum when the doping concentration of Ag cube NPs is 0.2%,and the corresponding enhancement factor is about1.89(?_ex=519 nm).The electric field distribution around Ag NPs is simulated by finite-difference time-domain(FDTD)method to analyze the NIR QC luminescence enhancement mechanism.(b)The relationship between three-photon NIR broad-band emission intensity of NaBaPO₄:Eu²⁺,Er³⁺and the concentration of Ag NPs is investigated.The results show three-photon broad-band NIR emission intensity reaches maximum when the doping concentration of Ag ball NPs is 0.5%,and the corresponding enhancement factor is about 1.395(?_ex=352 nm).The electric field distribution around Ag ball NPs is simulated by FDTD method to analyze the NIR QC luminescence enhancement mechanism.3.NaBaPO₄:Bi³⁺,Er³⁺phosphors are prepared.Four-photon NIR QC emission intensity of NaBaPO₄:Bi³⁺,Er³⁺can be greatly enhanced by the adjustment of Bi³⁺to crystal field.The maxium enhancement factor is about 10.64.Many research methods,including scanning electron miroscopy(SEM)comparison,X-ray diffraction(XRD)analysis and Eu³⁺spectral probe,are used to analyze the mechanism of the great enhancement.The results demonstrate that the crystal field is distorted when Bi³⁺is co-doped into NaBaPO₄:Er³⁺phosphors,which will increase the probability of Er³⁺4f-4f transition.4.Four-photon NIR QC emission enhancement of NaBaPO₄:Er³⁺and NaBaPO₄:Bi³⁺,Er³⁺with the addition of Li⁺is obtained,respectively.(a)The fluorescence spectra of NaBaPO₄:Li⁺,Er³⁺phosphors are measured and analyzed.The effect of Li⁺on four-photon NIR QC luminescence of NaBaPO₄:Er³⁺is investigated.The results show that four-photon NIR QC emission can be greatly enhanced when Li⁺ion is doped into NaBaPO₄:Er³⁺phosphors(?_ex=377 nm),and the maxium enhancement factor is about5.71.Many research methods,including XRD analysis,Juddy-Ofelt(J-O)intensity parameters comparison and Eu³⁺spectral probe,are used to analyze the mechanism of the great enhancement.The QC efficiency is calculated by the decay curves.And the results show that the QC efficiency of NaBaPO₄:Er³⁺can be enhanced when Li⁺is co-doped into NaBaPO₄:Er³⁺.(b)The fluorescence spectra of NaBaPO₄:Li⁺,Bi³⁺,Er³⁺phosphors are measured and analyzed.The effect of Li⁺on four-photon NIR QC luminescence of NaBaPO₄:Bi³⁺,Er³⁺is investigated.The results demonstrate that four-photon NIR QC emission of can be enhanced when Li⁺ion is co-doped into NaBaPO₄:Bi³⁺,Er³⁺phosphors(?_ex=377 nm),and the maximum enhancement factor is about 1.35.Moreover,the NIR emission enhancement mechanism of NaBaPO₄:Bi³⁺,Er³⁺with the addition of Li⁺is analyzed:as charge compensator,Li⁺ion can decrease the probability of non-radiation and enhance the NIR emission of NaBaPO₄:Bi³⁺,Er³⁺.5.According to J-O theory,and combining with absorbance spectrum of Er³⁺ion,the J-O intensity parameters and radiative parameters of Er³⁺in NaBaPO₄:Er³⁺phosphors co-doped with/without Li⁺ion are calculated.The rate equation NIR QC luminescence is established to analyze the dynamic process of NIR QC luminescence in NaBaPO₄:Er³⁺phosphors co-doped with/without Li⁺ion,and the theoretical QC efficiency of NaBaPO₄:Er³⁺phosphors co-doped with/without Li⁺ion is calculated.