Luminescence Modulation Of Rare Earth Ions In Inverse Opal Photonic Crystals And Fluorescent Sensing Applications

Since the concept of photonic crystal(PC) was proposed by Yablonovitch in 1987, it has attracted much attention and comprehensive studies. The long-range order periodicity of PCs can modulate electromagnetic, leading to the formation of photonic stop band(PSB). The way of PCs controlling the propagation of photons is the same as a semiconductor does for electron; PSB could prohibit light in a certain frequency just like the electron moves in the semiconductor. In recent years, the PCs have been applied in many potential technological fields such as semiconductors light emitters, photonic crystal filters, substrates for microwave antennas, sensors, and near-zero threshold lasers. Among all these special properties, a very important aspect is the modulation of PC on spontaneous emission when emmiters were embedded in PCs. Trivalent rare earth(RE) ions have 4fâ†'4f inners-shell transitions, possessing specific advantageous features, such as high luminescence yield, narrow emission line, and long decay time constant. It is necessary to study the modulation of the three-dimensional PCs on spontaneous radiation of rare earth luminescence material, which not only helps us to further understand the optical characteristic of PCs, but also greatly improve the luminescent efficiency of RE phosphors through inhibiting concentration quenching, temperature quenching, local thermal effect and reducing the non-radiative relaxation by taking advantage of the thin layer and macroporous matrix of PCs. In addition, rare earth doped upconversion nanoparticals(UCNPs) show incomparable advantage in biological sensors and bio-imaging in contrast to the traditional luminescent materials, including drastically improved signal-to-noise ratio, remarkable light penetration depth in tissue, less harm to cells and tissues in vitro or in vivo, and no photobleaching. Rare-earth doped upconversion nanoparticles have become one of the hottest issues in spectra-physics field. In this dissertation, we chose the rare earth doped nanoparticle as the main research object. Firstly, the modulation effect of PCs on the spontaneous radiation of Eu3+ ion as well as the inhibiting effect on energy transfer among rare earth ions was studied. Secondly, the ability of the special structure of PCs to effectively inhibit the nonradiative relaxation and local thermal effect was revealed through exploring the modulation effect of the special structure of PCs on the upconversion of rare earth doped oxides, to improve the upconversion efficiency of NaY(MoO4)2:Yb3+/Er3+ ultimately. Lastly, we studied the applications of the upconversion nanoparticles in biological fluorescence detection according to its optical properties. The main results are as follows:[1] Novel Na Y(MoO4)2:Eu3+ and NaY(MoO4)2:Tb3+, Eu3+ inverse opal photonic crystals(IOPCs) were prepared through the PMMA template by sol–gel method. Based on the emission spectra and fluorescence dynamics of NaY(MoO4)2:Eu3+ IOPCs and corresponding reference samples, the modulation of IOPCs on the emission spectra and fluorescence dynamics of Eu3+ was observed. We found that the spontaneous emission intensity of Eu3+ was weakened, when the emission band of Eu3+ ions overlapped with the PSB, meanwhile, the electron transition rate of Eu3+ was the same as in different IOPCs with different PSB. The lifetime of 5D0â†'7F2 transition in NaY(MoO4)2:Eu3+ IOPCs was prolonged 1.56 times in contrast to the reference samples, which was attributed to the change of effective refractive index instead of the change of local density of state. And more, the concentration quenching of Eu3+ ions and energy transfer from Tb3+ to Eu3+ were inhibited due to the structure of IOPCs. This work makes a great contribution to understanding of the PC effects on spontaneous emissions of rare earth ions and for novel devices of lighting and display.[2] Novel NaY(Mo O4)2:Yb3+/Er3+ IOPCs were prepared through the PMMA template by sol–gel method, and the modulation of IOPCs on the emission spectra and fluorescence dynamics of Er3+ were observed. Firstly, we observed a three-photon 2H9/2â†'4I15/2 transition in IOPCs which did not appear in the reference samples, indicating that the IOPCs were helpful for high-order upconversion luminescence. It was attributed to the inhibited radiative and nonradiative relaxation in IOPCs, which was further proved by upconversion dynamics. In addition, the local thermal effect caused by laser radiation was inhibited in IOPCs due to its periodic macroporous matrix. It can be concluded that the IOPC is an ideal device for improving the upconversion efficiency of oxide with large phonon energy due to its thin layers and macroporous matrix.[3] We developed a new type of mercury biosensor based on fluorescence resonance energy transfer(FRET) from NaYF4:Yb3+, Er3+ UCNPs to the CdTe quantum dots(QDs), which overcomes the lack of UV and Visible-excitable probes for mercury ions. The sensor can be used for mercury-ion sensing both in the PBS buffer and in serum with comparable performance, proving that the biosensor is capable of overcoming autofluorescence from serum excitation due to NIR excitation. When applied to detect mercury ions in human serum, the sensor had a good linear relationship(R = 0.996), and a low detection limit(15 nM), thereby easily detecting the 25 nM safety limit of mercury in the blood.