Novel Red Phosphor Doped With Mn⁴⁺Ons And Its Application

As a green light source in the 21st century,white LEDs are widely used in general lighting,liquid crystal display backlights,traffic lights,medical treatments,military and plant lighting,etc,due to its advantages of high efficiency,energy saving,environmental friendliness and long life.At present,the most popular approach for fabricating commercial white LEDs is by combining InGaN blue chip and YAG:Ce3+yellow phosphor.However,this kind of LEDs lack red light component in its spectrum,which result in high correlated color temperature(CCT>4500K)and low color rendering index(CRI<80).In summary,it is highly desired to exploit highly efficient novel red phosphors that can be efficiently excited by commercial blue diode chips.In recent years,compared with rare earth elements doped red phosphors,the Mn4+-doped red phosphors have attracted serious attentions for their low cost preparation and narrow emission bands.In particular,efficient red phosphors in deep red spectral region is highly desired in the field of agricultural lighting.In this thesis,a novel oxide red phosphor Mg3.5Ge1.25O6:Mn4+ and a oxyfluoride red phosphor Mg28Ge7.5O38F10:Mn4+ were prepared by the high-temperature solid-state method.The performances of the phosphors have been optimized systematically by controlling the synthesis temperature,synthesis procedure,sintering time and manganese ion doping concentration,etc.The phase,composition,morphology,luminescence properties,and thermal stability of the prepared samples were characterized by XRD,SEM,fluorescence spectroscopy,etc.The difference in phase,morphology and luminescence properties between fluoride red phosphor sample and oxide red phosphor sample was discussed in detail.The synthesized red phosphors were combined with blue chips to fabricate LEDs and the performance of the LEDs were tested.The red phosphors were found to have uniform particle sizes and irregular shapes.They exhibit strong and broad excitation band at blue light region and narrow red emission band peaked at 660 nm;Temperature-dependent spectral analysis shows that they possess good thermal stability,i.e.,the luminescence intensity of magnesium germanate and magnesium fluoride phosphors in 150? retained 92.7%and 96.8%of their intensities at room temperature,respectively.In addition,under the excitation of blue light,the samples demonstrate high photoluminescence quantum yield.The LEDs adopting these red phosphors emit at about 660 nm,which are promising for the applications in plant lighting.