| Rare earth doped up-conversion nano-crystals have attracted much interest because of their efficient energy transfer,high color purity,and they have significant applications in the fields of full color display,solid state laser,optical data storage,perovskite solar cell and bio-label.This paper studied the rare earth doped up-conversion nano-crystals in detail.The doping method,the doping amount,the composition ratio of rare earth and the synthesis temperature,test temperature,cation type of the materials had been investigated.X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),absorption spectra,up-conversion spectra,quantum yield,fluorescence dynamic curves were used to characterize the rare earth doped up-conversion nano-crystals.The studies on the rare earth doped up-conversion nano-crystals are mainly divided into the following stages:(1)The up-conversion luminescent SrGd2(WO4)2(MoO4)2:Yb3+/Tm3+/Ho3+nano-crystals were synthesized by hydrothermal method.The composition ratio of rare earth had been investigated.It indicated that when CYb3+=10 mol%and CYb3+/CTm3+/CHo3+=10:1.5:2,the emission intensities were the highest.The calculated CIE chromaticity coordinates(x,y)for SrGd2(WO4)2(MoO4)2:Yb3+/Tm3+/Ho3+nano-crystals fell into the white region of the chromaticity diagram.Three emission peaks,including blue emission peak,green emission peak and red emission peak were observed at 477,543 and651 nm corresponding to 1G4?3H6 and 1G4?3F4 transitions of Tm3+,5F4?5I8 and 5F5?5I8transitions of Ho3+respectively.The relationship between up-conversion intensity and excitation power revealed that blue emission at 477 nm was a three-photon absorption process,green emission at 543 nm and red emission at 651 nm were a two-photon absorption process.(2)The up-conversion luminescent SrGd2(WO4)2(MoO4)2:Yb3+/Ho3+nano-crystals were synthesized by hydrothermal method.The composition ratio of rare earth had been investigated.It indicated that when CYb3+=6 mol%and CYb3+/CHo3+=6:1.5,the emission intensities were the highest.The calculated CIE chromaticity coordinates(x,y)for SrGd2(WO4)2(MoO4)2:Yb3+/Ho3+nano-crystals fell into the green region of the chromaticity diagram.Two emission peaks,including green emission peak and red emission peak were observed at 545 and 651 nm corresponding to 5F4?5I8 and 5F5?5I8transitions of Ho3+respectively.The log-log plots of luminescence intensity and pump power revealed that red and green emission peaks were the two-photon absorption.(3)The up-conversion luminescent Ba Gd2(WO4)2(MoO4)2:Yb3+/Tm3+nano-crystals were synthesized by hydrothermal method.The composition ratio of rare earth had been investigated.It indicated that when CYb3+=6 mol%and CYb3+/CTm3+=4:1,the emission intensities were the highest.The calculated CIE chromaticity coordinates(x,y)for SrGd2(WO4)2(MoO4)2:Yb3+/Ho3+nano-crystals fell into the green region of the chromaticity diagram.Two emission peaks,including blue emission peak and red emission peak were observed at 475 and 650 nm corresponding to 1G4?3H6 and 1G4?3F4 transitions of Tm3+respectively.The log-log plots of luminescence intensity and pump power revealed that blue emission peak was the three-photon absorption,red emission peak was the two-photon absorption.(4)The up-conversion luminescent material Ba MoO4:Yb3+/Tm3+was prepared by hydrothermal method.The thermal stability and luminescence properties of the materials were studied by changing the synthesis temperature and test temperature.It indicated that,with the increase of temperature,the luminescence properties of all the samples were decreased obviously.But the luminescence properties of the samples that had been recrystallized at high temperature were better than that of the samples not recrystallized.The luminescence properties and thermal stabilities of the samples were the best when the temperature was 743 K.The grain size of the samples increased obviously after recrystallization above 743 K. |
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