Studies On Functions Of Surfactants In The Synthesis Of GdVO₄:Eu³⁺ By Hydrothermal Method

Rare earth resource was the dominant strategic resource in China. To achieve thedevelopment of rare earth resource with high value-added was our urgent strategictarget in recent years. The luminescent materials were the most important applicationarea of rare earth resource. The4f electron configurations in rare earth ions werevarious. The rare earth luminescent materials possessed excellent luminescence property,multifarious colours and high emission intensity. They were novel functional materialswith broad prospect of application, could have been applied in the lighting, displayequipments, optical variable inks, agricultural production, biolabeling and clinictrearment areas. During the process of nanomaterials development, to achieve a processroute to obtained particles with uniform morphology and grain size, excellentphotoluminescent property was still a key problem need to be solved by chemists andmaterials scientists. The surfactants were the most important factor in the soft chemistrysynthesie method that used to prepare functional nanomaterials. The researchment onthe influences and action mechanism of the surfactants in solution were not completesystem but were of great significance for synthesizing the rare earth functionalnanomaterials efficiently and conveniently in future. So it is important to focus on thesefoundational isssues.This dissertation was focused on the effects of surfactants on the morphology andproperty of europium doped orthovanadic gadolinium phosphors. The growthmechanism and luminescent evolution were discussed in detail. All the dissertation weremainly divided into six parts:(1) GdVO4:Eu3+powders were hydrothermally synth esized at180°C for24h in a wide pH range. The as-synthesized powders were characterized by X-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM),and photolum inescence (PL) spec troscopy. The XRD results showed that GdVO4:Eu3+with the tetragonal structure formed at pH<13as a single phase and Gd(OH)3formed atpH<13as a secondary phase. The SEM and TEM observation demonstrated thehydrothermally-induced morphological transformation of GdVO34:Eu+powders byaltering the pH of the synthesis solution. The possible mechanism for the morphologicaltransformation was proposed. The intensities of the prominent peaks at618nm in thePL emiss ion spectra of GdVO+4:Eu3powders considerably shift according to thespecific morphology. The luminescence intensity of the octahedron-and rod-likeGdVO4:Eu3+powders hydrothermally obtained at pH=3was the strongest one due tohigh packing density and high crystallinity as well as the extended reduction of theconcentration of inherent defect states or adsorbed species.(2) To discover the influence of CTAB on morphology and property of GdVO4:Eu3+crystals in a wide pH range. Hydrothermal synthesis route of fabricating GdVO34:Eu+phosphors using Gd2O3, NH4VO3, Eu2O3as the reacting precursors and CTAB assurfactant were proposed with different pH values. The obtained samples werecharacterized by XRD, SEM, TEM, and PL. The results revealed that the obtainedcrystal grain was micron in acid condition. And when pH was4, the final sample sizeshrank to nano-scale. It turned out well-dispersed nano-flakes with the size of about50nm. Further increased pH to10, the impurity Gd(OH)3was detected by XRD. Thesurfactant affected the final morphology of sample by changing the crystal growthdirection and assembled method obviously. Then it changed the final morphology.Otherwise, the luminescent properties were affected by grain size and crystallinity. Itturned out that square GdVO3+4:Eunano-crystal with well crystalline represented thestrongest emission intensity. The aggregation effect weakened the luminescent propertyof the samples.(3) We demonstrate that the critical issue of controllable growth of GdVO4:Eu3+crystalp articles is solved by tetradecyltrimethyl ammonium bromide (TTAB) in avariable pH range. The microstructure, morphology, and luminescence property of thephosphors were investigated by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and photoluminescencespectroscopy (PL). The results suggested that the surfactant TTAB was a key factor fordetermining the morphology of final GdVO4:Eu3+crystals. The in fluence of pH on thenucleation rate was studied as well. The PL results indicated that the PL property of theGdVO4:Eu3+phosphors was crucially impacted by the micro-structure and morphology.All the phosphors mainly showed strong red emissions at615and618nm originatingfrom the hypersen-sitive transition5D70â†'F2of Eu3+ions. The nano-sized phosphorsshowed prominent PL properties due to the grain size effect. The crystalline state andthe microstructure of the products also affected the PL performance.(4) Europium doped micro-/nano-crystalline gadolinium vanadate (GdVO4:Eu3+)phosphors have been successfully achieved via a facile hydrothermal route assisted withDTAB at various pH values from gadolinium oxide, europium oxide, and ammoniummetavanadate. The structure, morphology, and photolumines-cent property of the finalproducts were characterized by X-ray powder diffraction (XRD), scanning electronmicroscopy (SEM), transmission electron microscopy (TEM), and photolu-minescent(PL) spectra, respectively. It was found that pure phase GdVO3+4:Eumicrocrystals withinteresting shapes fabricated at180°C for24h in pH1. Further, the fantasticmorphological evolution from microscale to nanoscale due to the pH value increasing.We obtained well-dispersed nanoflakes around50nm in pH7and10. And samplesynthesized in pH10had better crystallinity. In addition, the intensities of excitationand emission spectra were varied with the morphological change. Nanoflakes phosphorsshowed the strongest PL intensity than other powders. Besides, the PL property wasenhanced by crystalline state and size shrinking.(5) Europium doped micro-/nano-crystalline gadolinium vanadate (GdVO4:Eu3+)powders were successfully fabricated via a facile hydrothermal route. To investigate theinfluences of sodium dodecyl sulfonate (SDS) and pH on the morphology andluminescent properties of GdVO4:Eu3+phosphors, different amounts of SDS were addedin the hydrothermal reaction system under various pH values. The structures andmorphologies of the final products were characterized by X-ray powder diffraction(XRD), scanning electron microscopy (SEM), and transmission electron microscopy(TEM). Several interesting morpholo-gies of GdVO4:Eu3+powders were obtained, including tetragonal, octahedron, rod-like, and dendritic. The results indicated that thepH determines the nucleation rate of GdVO34:Eu+crystals in the solution, and the SDSaffects the crystal growth pattern by changing growth direction and forming micelles.Moreover, possible mechanisms for morphological evolution are also presented. Thephotoluminescent (PL) proper-ties of the products were also characterized. All thesamples exhibited the characteristic fluorescence of Eu3+ion. In addition, the intensitiesof excitation and emission spectra varied with the morphological change. The productwith nanocrystal morphology showed the strongest PL intensity among all the sam-pleswith different morphologies. Besides, the PL property was enhanced with goodcrystalline state, but weakened by serious aggregation.(6) Europium doped micro-/nano-crystalline gadolinium vanadate (GdVO3+4:Eu)phosphors have been successfully achieved via a facile hydrothermal route assisted withPVA at various pH values. The structures and morphologies of the final products werecharacterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM),and transmission electron microscopy (TEM). The results suggested that the surfactantPVA was a key factor for determining the morphology of final GdVO34:Eu+crystals.The PL results indicated that the PL property of the GdVO4:Eu3+phosphors wascrucially impacted by the micro-structure and morphology. The PL property wasenhanced with good crystalline state...