Fluorescence Enhancement And Color Modulation Of Rare Earth Doped Gadolinium Molybdate

Rare earth doped up-conversion fluorescent materials,possessing non-linear optical ability to convert multi-low energy photons into high energy photons,have potential applications in many fields,including solar cell,bio-imaging,temperature sensing,3D imaging,and so on.However,the lower up-conversion efficiency in rare earth doped up-conversion fluorescence materials dramatically restricts their applications.And their applications in colorful imaging are limited by the difficulty in adjusting emission color radiated from rare earth doped up-conversion fluorescence materials.Thus,multi-layer structure,Au islands’ local surface plasma resonance（LSPR）and co-excitation with two lasers were utilized to enhance rare earth doped gadolinium molybdate.The energy transfer and cross relaxing between rare earth ions and the non-steady up-conversion processes were used to modulate the emission color.The main contents of this thesis are as follows.Based on the large cross-section of Yb³⁺ at ⁹80 nm,we analyzed effect of Yb³⁺ ions,doping in the coating layer,on emission intensity from bi-layer and sandwitch structured thin films.Combining the energy migration between rare earth ions,doping in different layer,and the restrain of surface quenching,we explained the emission enhancement from bi-layer and sandwitch structured thin films.And the influence of Yb³⁺ ions’ concentration on emission intensity has also been studied.In addition,the applications of sandwitch structured thin films in high resolution imaging has been discussed through the comparison between the enhancement effects of sandwich structure and high laser power on multiphoton up-conversion photoluminescence.The outstanding enhancement around short waveband has been explained via the high excited state energy transfer.According to LSPR of Au islands,with its absorption peak at ⁵33 nm,we realized obviously green emissions enhancement from Au islands modified Er³⁺/Yb³⁺doped gadolinium molybdate thin films,prepared via the combination of electrostatic self-assembly and spin coating.After detecting the life time of green emission radiated from thin films with and without Au islands,we analyzed the impact of coupling between Au islands and Er³⁺ ions on green emission’ radiation transition rate and intensity.Moreover,the optical thermometry of rare earth doped up-conversion materials has also been widely concerned.Therefore,we studied the temperature dependent fluorescence intensity ratio（FIR）and emission lifetime of the Au islandsmodified fluorescent thin films.The applicable temperature ranges of these two optical thermometry method have been discussed.We studied the effect of co-excitation with two lasers on up-conversion emission intensity and color through using the accordance between two lasers’ energies and the energy gap of Er³⁺.The intensity change of green emissions from Er³⁺/Yb³⁺ doped gadolinium molybdate powder,under co-excitation with 980 and 808 nm lasers,has been investigated.Based on the match between 980 and 808 nm lasers’ energies and the specific energy gap of Er³⁺,the reason for power dependent enhancement factor of green emissions has been discussed.In addition,the change of emission color radiated from Er³⁺/Yb³⁺ doped gadolinia powder under co-excitation with 980 and 1550 nm lasers has been studied.And the co-excited up-conversion processes under different excitation condition has been researched through the needed photon numbers of green and red emissions radiating.On the grounds of the energy transfer(Eu³⁺-Ho³⁺)and the cross-relaxing(Ce³⁺-Ho³⁺),we studied the effect of Eu³⁺,Ce³⁺ doping concentration in Ho³⁺/Yb³⁺doped gadolinium molybdate powder on the sample’ emission color.Besides,we discussed the influence of 980 nm laser’ pulse width and repetition frequency on the emission color of Ho³⁺/Tm³⁺/Yb³⁺ doped gadolinium molybdate powder.Combing the up-conversion processes of red(Ho³⁺),green(Ho³⁺)and blue(Tm³⁺)emissions and the time dependent emission intensity,the non-steady up-conversion processes of Ho³⁺-Tm³⁺-Yb³⁺ system has been discussed under excitation with different 980 nm laser’ pulse width and repetition frequency.