Preparation And Study Of Fluoride Matrix Phosphors For White LEDs

Fluoride matrix red phosphors used in white LEDs have attracted more and more attention from researchers at home and abroad due to their excellent optical properties.The existing liquid phase synthesis methods have the disadvantages of low purity,long reaction time,and high cost of raw materials.In this thesis,five series of fluoride matrix red phosphors were successfully prepared by ion exchange-precipitation method.They are Cs₂GeF₆:Mn⁴⁺,Cs₂SiF₆:Mn⁴⁺,Cs₂TiF₆:Mn⁴⁺,Cs₂ZrF₆:Mn⁴⁺,Rb₂GeF₆:Mn⁴⁺,Respectively.The phase and morphology were characterized;the luminescencepropertiesatroomtemperaturewereinvestigated;Concentration-dependence and Temperature-dependence emission spectra were studied;The relationship between ZPL emission intensity and crystal structure symmetry,and the hypothesis of resonance emission enhancement?REE?were explored and verified in detail;White LED devices were fabricated with the most excellent Cs₂GeF₆:0.1Mn⁴⁺and Rb₂GeF₆:0.04Mn⁴⁺samples.The details are as follows:Firstly,potassium source were provided from KHF₂,then the K₂MnF₆ precursor was prepared by reducing the KMnO₄.The K₂MnF₆ precursor obtained was found to be high purity.Secondly,The fluoride substrate was prepared by the reaction of dioxide and CsF/RbF,followed by the addition of different amounts of K₂MnF₆,the target product with different Mn⁴⁺doping concentrations was prepared by ion exchange method.X-ray diffraction?XRD?and scanning and electron microscopy?SEM?are to investigatephaseandmorphology.Concentration-dependentand Temperature-dependent luminescence spectra are to study the effects of concentration and temperature on luminescence properties.At the same time,the thermogravimetric and high-resolution spectroscopy tests were compared and analyzed the thermal properties and the optical properties at room temperature of the phosphors.The verification of the REE hypothesis is to further analyze the relationship between crystal structure and luminescence properties.The results show that the samples are all pure phase and exhibit good crystallinity,meanwhile,showing good thermal properties and thermal stability.The result of the REE hypothesis shows that,in the crystal lattice,the ordered Mn⁴⁺ions and the obtained organized d value,as well as the appropriate distance between Mn⁴⁺-Mn⁴⁺in the specific case support the occurrence of the REE process.Lastly,the red phosphor Cs₂GeF₆:0.1Mn⁴⁺,blue InGaN chip,yellow phosphor YAG:Ce³⁺were assembled into WLED devices and the device exhibits a high luminous efficiency over 100 lm/w,a high color rendering index?⁸8.6?and low color temperature?³684 K?,Showing a good photoelectric performance.The white LED device assembled by Rb₂GeF₆:0.04Mn⁴⁺red phosphor exhibits a high color rendering index of Ra=89.2 and a low color temperature of CCT=3258 K.Compared with the device prepared by Cs₂GeF₆:0.1Mn⁴⁺,the photoelectric performance is higher.Therefore,Cs₂GeF₆:Mn⁴⁺and Rb₂GeF₆:Mn⁴⁺are very promising red phosphors.