Research On Synthesis And Luminescent Properties Of Mn⁴⁺-doped Fluoride Phosphors

The development of semiconductor technology, especially thelarge-scale application of GaN-based LED, promotes the electronicindustry becoming friendlierto the environment.Owning to theuniquecoordinate entvironment, complex fluoridesare considered as theappreciate host material for several ions, particularly Mn4+ion which ismuch cheaper than rare earth ions because it is rich in mineral resources.In this dissertation, two Mn4+-doped fluoride phosphors:BaSiF6:Mn4+and BaTiF46:Mn+have been synthesized by usinghydrothermal method and chemical etching. To our knowledge, there arefew reports concentrating on the synthesis of Mn4+-doped alkalinefluorides by hydrothermal method. The composition, morphology andluminescent properties of the as-prepared samples were also investigatedby XRD, SEM, TG-DSC, Raman spectrum and PL&PLE spectra. Allresults show that the as-prepared samples possess the potentialapplication in WLEDs attributed to their good crystallinity, efficientexcitation by GaN chips and strong emission at630nm which locates atthe visible red region.Our specific conclusions are as follows: (1) Mn4+ion will be substitutedfor the Si4+and Ti4+ion which are inthe SiF2-6andTiF2-6octahedron, respectively, resulting in the formationofMnF2-6. The Mn4+are also identified by the X-rayphotoelectronspectroscopy (XPS) measurement, which further confirms that thestoichiometric compositionof the red phosphor is nomanganeseoxide andother impuritieshave beendetected in the as-synthesized samples.(2) The luminescent centers of sharp red emission at630nm areascribed to the Mn4+ions in theoctahedral site of Ba2SiF6andBa2TiF6gained by the activation of local vibration modes2Egâ†'4A2g.(3) Our present work reports a detailed investigation ofreaction time,Temperature of redphosphor BaSiF6:Mn4+and BaSiF6:Mn4+,Theconcentrations ofHF andKMnO4are also researched. Optimum synthesisconditions are obtained.(4) The reaction mechanism has been investigated as well. Redoxreaction occurs between KMnO4and HF while the resulting Mn4+wouldbe chelated by the excess F-and eventually changes into MnF-6(5) The Thermogravimetric analysis shows that BaSi1-xMnxF6andBaTi1-xMnxF6red phosphors decompose at400℃, which, namely, both ofthem possess the potential application in WLEDs.(6) The samples have been doped into the commercialized phosphorYAG:Ce. The color rendering index enhanced from68.2to82.1.