Synthesis Of Gold Nanoparticles And Their Application In Enhancing Upconversion Luminescence And Optical Fiber Laser

In recent years, gold nanoparticles have found great potential applications in thefield of enhancing upconversion luminescence, nonlinear optics, and biomedicaldetection for their special surface plasmon resonance, large third-order nonlinearity,and good biocompatibility. Much work has been done in these fields. In the field ofenhancing upconversion luminescence, gold nanoparticles have been assembled withdifferent upconversion luminescence materials. Enhancement effect of thulium ionand erbium ion has been obtained. The enhancement ratio was from five to hundreds.However, the research of the other rare earth ions is very few. In the studying offluorescence enhancement mechanism, rare attention has been paid to the variationof the energy transfer process. In the field of nonlinear optics, various compositesand films of gold nanoparticles have been synthesized. The nonlinear coefficients ofgold nanoparticles in these systems were detected. In contrast, there is rare report onapplying gold nanoparticles in building pulsed lasers. Au@NaYF₄:Gd,Yb,Tm hybridnanostructures were synthesized. Both upconversion enhancement and magneticproperties were obtained in these nanostructures. Gold nanoparticles films weresynthesized and their nonlinear properties were studied. This thesis presented asystematic research and the main results were outlined as followings:（1） Uniform and single-crystal α-NaYF₄:Yb³⁺,Tm³⁺NC_s were successfullysynthesized via a simple template-free hydrothermal route with CA as modifiersunder different reaction conditions. Through tuning the ratio of CA/Ln, the reactiontime and the reaction temperature, the morphologies and the UC luminescenceproperties of the samples were studied. The optimal UV UC emissions wereobtained for the sample with the ratio of CA/Ln as4:1synthesized at180C for12hin our experiment. The5-photon UC emissions of Tm³⁺ions are stronger than the4-photon UC emissions and the3-photon UC emissions. To our knowledge, it is thefirst time to observe such intense UV UC emissions with α-NaYF₄. Compared with the TC modified β-NaYF₄:Yb³⁺,Tm³⁺NC_s, the-NaYF₄NC_s have longerfluorescent lifetimes for the blue and ultraviolet upconversion emissions. Such aspectral character has led the stronger UC luminescence of the α-NaYF₄NC_s thanthat of the β-NaYF₄NC_s.（2） Au NPs attached β-NaYF₄NC_s codoped with Gd³⁺-Yb³⁺-Tm³⁺（ANNC_s）were synthesized by a facial hydrothermal and solution method. Under the excitationof980nm, UV UCL enhancement was observed in the nanostructures. The largestenhancement factors of6^I_Jâ†'8^S_7/2(Gd³⁺) and6^P（5/2）â†'8^S_7/2(Gd³⁺) were76and47,which were larger than those of Tm³⁺emissions. It is for the first time to ourknowledge that emission enhancement of Gd³⁺ions was obtained. The mechanism ofUV UC emission enhancement in the prepared nanostructures was discussed in detailbased on the fluorescent dynamics of Gd³⁺, Yb³⁺, and Tm³⁺ions and surface plasmonfield enhancement effect was considered as the main reason for the enhancement. TheGd³⁺-Yb³⁺-Tm³⁺co-doped nanostructures also exhibited proper paramagnetism inroom temperature.（3） Single-wall carbon nanotubes （SWNT_s） saturable absorber was synthesizedand a ring cavity erbium-doped fiber laser （EDFL） was set up based on this saturableabsorber. Stable passively soliton mode-locking was achieved for a threshold pumppower of³0mW, with a repetition rate of33MHz at1560nm. The pulse width was630fs for a pump power of¹25mW. The output power increases linearly from0.05to0.68mW with increasing the pump power from35to105mW, and thecorresponding average optical-to-optical efficiency is about0.4%.（4） We synthesized gold nanoparticles by using citrate as reductant and mixedthem with SWNTs as a new saturable absorber. When the new SA was used inerbium-doped fiber laser, the mode-locking threshold pump power was adjusted. Thethreshold pump power firstly increased from30.5mW to16mW, and then decreasedwith the concentration increase of gold and the concentration for the lowest pumppower is0.6. Our experiment results provide a new program for reducing themode-locking threshold pump power.（5） Gold nanocrystals with diameters of20nm were prepared by using citrate as reductant. The surface plasmon peaks of the obtained samples were at523nm. TheGNC_s were mixed with sodium carboxymethylcellulose （NaCMC） to formGNC_s-NaCMC films. These films have a broadband absorption from500to2000nmand appeared saturable absorption property. When the SA was used in anerbium-doped fiber laser （EDFL）, stable passively Q-switching was achieved for athreshold pump power of³0mW, and3.2s pulses at1560nm with a repetition rateof24.2kHz and an average output power of6.23mW were obtained for a pumppower of¹25mW.