| Owing to the promotion of the concept of energy saving and environmental protection,white light emitting diodes(LEDs)have been widely used in the field of illumination and display due to their excellent properties such as high energy efficiency,high reliability,long operating time,and environmental benefit.The properties of phosphors have a direct impact on the optical properties of white LED devices.until now,the most common and simple method to obtain white-light LEDs is to combine an In Ga N-based blue LED with a yellow phosphor material,such as YAG:Ce.However,it still has a low colour rendering index and high correlated color temperature due to lack of red component.The addition of red phosphor excited by blue light to the YAG phosphor could solve these problems to a certain extent,but the costly synthesis and the irreversible oxidation degradation of(oxy)nitrides are still the obstacle and weakness,limited the application of white LEDs in warm white lighting.In this paper,the first one is to present a simultaneous non-luminous ion co-substitution design strategy and delicately prepare a series of garnet phosphor by high temperature solid phase sintering and liquid phase chemical co-precipitation,the second one is to modulate the emission spectrum wavelength of garnet phosphor by doping Zn2+ and compare the crystal field strength by calculation.The last one is to optimize energy transfer processes of Ce3+?Cr3+ by different ions and increase luminous components in red light region:Firstly,the effect of preparation process on the morphology and luminescent properties of phosphors was investigated,and the process parameters of high-temperature solid-state method and co-precipitation method were optimized.The optimum preparation process of co-precipitation precursor system was determined,and the fluorescence powder with uniform dispersion,good morphology and size of 500 nm or so was obtained.on the other hand,by high temperature solid phase method,after adding the binary flux and calcining for 3 hours at 1350?,the phosphors with uniform particles,good dispersibility and pure substance phase can be obtained.Compared with commercially available phosphors,the luminous intensity of phosphors produced by the high-temperature solid-state method increased by 18.2 %.Secondly,the effect of different site substitutions on the properties of{A}3[B]2(C)3O12 garnet phosphors was investigated through analyzing the relationship between the structure and properties of garnet phosphors.This can cause lattice distortion when the incorporation of Gd3+ into A site or Mg2+-Si4+ replacing B-C site in YAG.to achieve a further red shift in the emission spectrum.By co-doping other non-luminescent ions(Zn2+,Li+,etc.),the improvement of the luminous intensity of the above-mentioned phosphor is achieved,after adding Zn2+,the luminescence intensity is increased by 170 % at the optimum doping ratio(x = 0.1),which is accompanied with a red shift of the emission peak at about 23 nm,the mechanism of red shift of the spectrum was analyzed.Optimized phosphors were tested in LED packaging.The color rendering index can reach 81.7,which is 17.7 % higher than that of YAG:Ce3+phosphor.The correlated color temperature reaches 4367 K.The CIE chromaticity coordinates can reach(0.3694,0.3918),which has great potential for commercial application.Finally,take Ce3+-Cr3+ as the research object,the effect of the non-luminescent ion-doped garnet matrix on the energy transfer effect was studied.The co-doping of Gd3+and Zn2+solved the problem that the reduction of luminous efficiency of the luminescent ion during energy transfer.The doping of Gd3+ increased the spectral overlapping area between Ce3+and Cr3+.Compared with the blank group,doped with Zn2+(x = 0.1)can make Cr3+ emission peak strength increased by 26.5%,which has positive significance for improving the luminescent properties of white LED devices. |
PDF Full Text Request