| Rare earth doped luminescent materials have wide potential applications in the fields of lighting, display, laser, biosensor, anti-counterfeiting, etc. Especially, the solid state lighting resource employed in the vehicles of ships, naval vessels and submarines can reduce the consumption of energy and improve the self-supportability of vehicles efficiently. With the development of nanotechnology, low-dimensional nanostructured materials have sparked a worldwide interest due to their unique electronic, optical, and mechanical properties and their potential applications in nanodevices and functional materials. It is well known that these properties can be influenced greatly by the structure, morphology and size of nanomaterials. Therefore, the controlled syntheses of nanomaterials are very important for both fundamental research and practical applications. In this thesis, we synthesized different rare earth ions doped micro-/nano-materials through various chemical methods and studied their growth process and luminescent mechanism. The main contents in this thesis are as follows.(1)3D structured CaWO4:Tb3+microspheres were prepared via a sonochemical route. XRD and SEM results displayed that the surface of each microsphere is very rough and contains a lot of small nanoparticles. The formation mechanism of3D structured CaWO4:Tb3+microspheres were studied. It was found that3D structured CaWO4:Tb3+microspheres are assembled by spindles. Moreover, PEG-600plays an important role in the formation of microsphere. Under UV excitation,3D structured CaWO4:Tb3+microspheres exhibit intense green emission. The energy transfer processes from WO42-to Tb3+and between5D3and5D4levels of Tb3+ions were observed in the3D structured CaWO4:Tb3+microspheres. It was also proved that electric dipole-dipole interation is the main mechanism for energy transfer between5D3and5D4levels of Tb3+.(2) NaY(WO4)2:Eu3+microflowers were prepared via microwave-assisted hydrothermal process. XRD and SEM results showed that the product is pure NaY(WO4)2:Eu3+. Moreover, the final morphology of product was influenced slightly by calcination process. The growth process of NaY(WO4)2:Eu3+microflowers were studied. It was found that the NaY(WO4)2:Eu3+microflowers are assembled by many nanoflakes. The luminescent properties of NaY(WO4)2:Eu3+microflowers were studied in details. The crossover process is responsible for fluorescent quenching induced by high temperature.(3) Persimmon-like NaLa(WO4)2:Eu3+,Tb3+microcrystals were prepared via one-pot hydrothermal process. XRD and SEM results showed that Na3Cit plays an important role in the formation of persimmon-like NaLa(WO4)2:Eu3+,Tb3+microcrystals. The energy transfer from Tb3+to Eu3+can be observed in the persimmon-like NaLa(WO4)2:Eu3+,Tb3+microcrystals. Moreover, with the increase of Eu3+concentration, the energy transfer efficiency increases and the luminescent color can be tuned efficiently.(4) Eu3+and Dy3+doped Y2(MoO4)3microflowers were prepared by co-precipitation method. SEM results revealed that Y2(MoO4)3microflowers are assembled by many nanoflakes. Moreover,β-cyclodextrin can control the size and morphology of the products in the synthesis process. Therefore, β-cyclodextrin assisted co-precipitation reaction may be an efficient approach for preparation of inorganic micro-/nano-materials with special morphologies. Finally, it was confirmed that the energy transfer mechanisms in Eu3+and Dy3+single doped molybdate phosphors are exchange and electric dipole-dipole interaction, respectively.(5) La2(MoO4)3:Eu3+nanoparticles were prepared via co-precipitation method. XRD and SEM results showed the crystal structure of the resultant La2(MoO4)3:Eu3+nanoparticles is tetragonal phase. Moreover, the average size of La2(MoO4)3:Eu3+nanoparticles is about88.5nm. The electron-phonon coupling properties were studied. It is found that the maximum phonon energy of La2(MoO4)3:Eu3+nanoparticles is about1900cm-1. It was also confirmed that the mechanism of concentration quenching for Eu3+is a self-quenching process. Additionally, a new route for J-O parameters calculation was developed, in which the refractive index of host might be estimated.(6) YF3:Tb3+,Eu3+micro-/nano-crystals were prepared through a solvothermal process, and the uniform sandwich-structural rhombus-like YF3:Tb3+,Eu3+particles could be obtained by well controling the reaction parameters. The growth mechanism of sandwich-structural rhombus-like YF3:Tb3+,Eu3+particles were studied. It was found that EG plays double functions in the formation of sandwich-structural rhombus-like YF3:Tb3+,Eu3+particles. Finally, the luminescent properties of sandwich-structural rhombus-like YF3+:Tb3+,Eu3+were studied. The energy transfer from Tb3+to Eu3+in the sandwich-structural rhombus-like YF3:Tb3+,Eu3+particles was conformed to be electric dipole-dipole interaction. (7) Orthorhombic EuF.3submicrospheres were prepared via a hydrothermal process. The phase transition of EuF3phosphor from orthorhombic phase to hexagonal one was observed when rare earth ions with larger ionic radius were introduced into the reaction system. Moreover, in the phase transition process it was found that the size and assembling degree of the product decreased with the increase of rare earth ions concentration or radius. The rare earth ions-induced phase transition was attributed to the decrease of energy from orthorhombic phase to hexagonal one. Meanwhile, the luminescent enhancement can be observed.(8) NaYF4:Er3+,Yb3+microtubes were prepared through a hydrothermal process with YF3:Er3+,Yb3+submicrotubes as precursor. The phase transition process of NaYF4from cubic to hexagonal was observed with the increase of reaction time. Under980nm exaction, the uponversion luminescent intensities of hexagonal NaYF4:Er3+,Yb3+microtubes is10times as that of the cubic sample. It was confirmed that both the green and red upconversion emissions are two-photon process.(9) Hexagonal NaEuF4micro-/nano-crystals were prepared via a hydrothermal process in the presence of Na3Cit. Different morphologies of hexagonal NaEuF4micro-/nano-crystals were obtained by changing the pH value and Na3Cit/Eu3+molar ratio. The formation mechanism of hexagonal NaEuF4micro-/nano-crystals was studied. Under394nm excitation, it was found that the luminescent intensity of hexagonal NaEuF4micro-/nano-crystals increased with the decrease of size of product, which was attributed to the fact that the energy transfer from Eu3+to quenching center was hindered.(10) Bulk and nanosized GdVO4:Dy3+phosphors were prepared via a simple co-precipitation process. The characteristic emissions from4F9/2level of Dy3+in the bulk and nanosized samples were observed. It was found that electric dipole-dipole interaction is hindered in the nanosized samples based on the analysis of the dependence of luminescent intensity on concentration. The decay time of the4F9/2level in the nanosized GdVO4:2mol%Dy3+sample is determined to be longer than that in the0.3mol%Dy3+doped bulk sample. Moreover, the fluorescent lifetime of this level in the nanosized sample is strongly dependent on the index of refraction of the medium surrounding the nanoparticles and a0.68filling factor is obtained. The intrinsic radiative lifetimes and internal quantum efficiencies of the4F9/2level of Dy3+in the nanosized and bulk samples were obtained, which indicated that the internal quantum efficiency of nanosized sample was higher than that of the bulk sample. (11) Three dimensional (3D) architectures YBO3phosphors were prepared via an ionic liquid assisted hydrothermal process and characterized by XRD, FE-SEM and photoluminescence (PL). It was found that the pH value and ionic liquid played an important role on the morphology of products. Self-assembly evolution of microblocks and Ostwald ripening process were assigned to the possible formation mechanism for the tyre-like YBO3microspheres based on the analysis of time-dependent experiments. Compared with corresponding bulk, the tyre-like YBO3:5mol%Eu3+microspheres demonstrated a red shift of the charge transfer band (CTB) with a long excitation tail at the long wavelength side of the CTB, and high improved chromaticity in the spectra. Two kinds Eu3+environments in the tyre-like sample, namely, interior and outside Eu3+, were found by exciting the samples at different excitation wavelengths. Finally, fluorescent decays and Judd-Ofelt (J-O) theory were utilized for analysis of local crystal environments around Eu3+ions in the tyre-like and bulk phosphors. |
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