Investigation On The Synthesis And Down-Conversion Luminescence Of Rare Earth Ions Doped Functional Nano-materials

With the development of society, the depletion of energy and environmentissues resulting by energy consumption have become a bottleneck restricting thesustainable development of economic. Therefore, white LED lighting with energysaving and environmentally friendly advantages have receieved more and moreattentions in recent years. In this thesis, the synthesis and downconversionluminescence properties （photoluminescence and quantum cutting） of rareearth ions doped functional nano-materials were systematically investigated，including rare earth ions doped glass ceramics and fluoride nanocrystals. Themain research results are described as follows:1. The components of precursor silicate glasses were determinedaccording to the MO-SiO₂（M=Ca, Sr, Ba）glass phase diagram. Eu²⁺dopedglass ceramics containing Ba₂Si₃O₈and MSiO₃（M=Ca, Sr, Ba） nanocrystalswere obtained after the proper heat-treatment of the glass samples. Thecrystal phase, morphology of nanocystals and spectroscopic properties ofEu²⁺doped glass ceramics containing Ba₂Si₃O₈and MSiO₃（M=Ca, Sr, Ba）nanocrystals were studied in detail via measurements of XRD, TEM, Raman,absorption, excitation and emission spectra, and lifetime decay. The Eu²⁺activated Ba₂Si₃O₈glass ceramics exhibited broad emission band centered at518nm due to the4f65d1→4f7transition of Eu²⁺, and the emission intensityincreased with the rising of heat treatment temperature. The excitationspectra of the glass ceramics from300nm to420nm covered the UV-NUVregion. Compared with the glass, the emission intensity of Eu²⁺activatedglass ceramics was much stronger, and the peak wavelength shifted towardshorter wavelength. According to the photoluminescence （PL） spectra, theCIE chromaticity coordinates of the Eu²⁺activated glass and glass ceramicswere calculated. As for Eu²⁺activated MSiO₃（M=Ca, Sr, Ba） glass ceramics, their excitation bands mainly extend from450nm to250nm. With UV lightexcitation, the Eu²⁺emission in CaSiO₃, SrSiO₃and BaSiO₃shows blue,green and yellow colors centered at440nm,505nm and555nm, respectively.The critical Eu²⁺concentration was studied and determined.2. Eu²⁺/Sm³⁺and Eu²⁺/Dy³⁺co-doped silicates glass was prepared byhigh temperature melting in reducing atmosphere. And the Eu²⁺/Sm³⁺andEu²⁺/Dy³⁺co-doped SrSiO₃transparent glass ceramics were obtained afterheat-treatment. X-ray diffraction （XRD） and Raman spectra confirmed theformation of SrSiO₃nano-crystals in the glass matrix. The samples’excitation and emission spectra were measured. The glass ceramics’luminescence properties with different molar ratio of Eu²⁺/Sm³⁺andEu²⁺/Dy³⁺were also studied and the corresponding chromaticity coordinateswere calculated. With UV light excitation, A broad emission band regionfrom400nm to550nm （green） due to the4f65d1→4f7transitions of Eu²⁺wasobserved, as well as several sharp emission peaks at563nm,600nm,646nmand713nm ascribed to the4G5/2→6HJ/2transitions of Sm³⁺, and483nm,575nm due to the4F9/2→6H15/2and4F9/2→6H13/2transitions of Dy³⁺. Theultraviolet light-emitting diode （UV-LED） excitable glass ceramics emittingwhite light were obtained by controlling the molar ratio of Eu²⁺/Sm³⁺(Dy³⁺).The concentration quenching effect of Sm³⁺(Dy³⁺) and the energy transfermechanism from Sm³⁺(Dy³⁺) to Eu²⁺were analyzed by the means of emissionspectra and lifetime decay.3. The effects of synthesis conditions (PH values, F-/Gd³⁺molar ratio,reaction temperature and time, organic additives) to the crystal structure andmorphology of GdF₃nanocrystals were studied. Tb³⁺/Yb³⁺and Pr³⁺/Yb³⁺co-doped GdF₃nanocrystals were prepared by a facile hydrothermal method.Under excitation at483nm, GdF₃:1%Tb³⁺,5%Yb³⁺not only shows thecharacteristic emission of Tb³⁺in the visible region, but also exhibits theunique emission (²F_5/2→²F_7/2) of Yb³⁺in NIR region. As for Pr³⁺/Yb³⁺co-doped GdF₃nanocrystals, the NIR luminescence of Yb³⁺were alsoobserved under441nm excitation. In addition, with increasing theconcentration of Yb³⁺, the luminescence intensity of Tb³⁺and Pr³⁺decreased gradually, whereas that of Yb³⁺initially increased and then decreased，reached the maxim at10mol%Yb³⁺and5mol%Yb³⁺respectively. The resultsindicated that the energy transfer of Tb³⁺→Yb³⁺and Pr³⁺→Yb³⁺can beascribed to cooperative downconversion and high efficient first orderdownconversiton respectively. And the max quantum yield of Tb³⁺/Yb³⁺andPr³⁺/Yb³⁺co-doped GdF₃nanocrystals can reach at139.3%and165.3respectively.4. Nd³⁺/Yb³⁺co-doped NaGdF₄nanocrystals were synthesized via simplehydrothermal synthesis using C6H5O8Na3as organic additive. The crystallineprocess and morphology of the prepared NaGdF₄nanocrystals wereinvestigated through XRD, SEM and TEM measurement. The NaGdF₄nanocrystals show high hexagonal crystalline purity. Under excitation at376nm, NaGdF₄:1%Nd³⁺,5%Yb³⁺not only shows the characteristic emissionof Nd³⁺in the visible and NIR reigion, but also exhibits the unique emission(²F_5/2→²F_7/2) of Yb³⁺in NIR region. In addition, with increasing theconcentration of Yb³⁺, the luminescence intensity of Nd³⁺decreasedgradually, whereas that of Yb³⁺initially increased and then decreaseed，reached the maxim at5%Yb³⁺. The results indicated that the energy transferNd³⁺→Yb³⁺can be ascribed to two step downconversion （quantum cutting）,and the max quantum yield can reach at158.7%.