Study On Fabrication And Luminescence Properties Of High Color Rendering Pc-WLED Devices

In recent years,with the rapid development of semiconductor lighting technology,white light-emitting diodes(WLEDs)have been widely applied in lighting,display and medical fields,owing to the outstanding merits of high efficiency,high luminous flux,low energy consumption,long lifetime and eco-friendliness.As is known,the most mainstream approach to fabricating commercial phosphor-converted WLEDs(pc-WLEDs)is the combination of In Ga N blue(440?470 nm)chips with Y₃A_l5O₁₂:Ce³⁺(YAG:Ce³⁺)yellow phosphor in organic resin.At present,this method has undesirable shortcomings,including a low color rendering index(CRI,R_a<80)and a high correlated color temperature(CCT>5000 K).According to previous studies,filling the cyan spectral valley from 470 to500 nm and the lack of deep red components above 650 nm are important factors to improve the R_a of pc-WLEDs.It is known that there is a trade-off between R_a and LE.As a result,how to improve the LE of pc-WLEDs while maitaining a high R_a is also a key issue worthy to be studied.To solve the above problems,this article focuses on the fabrication and luminescence properties of high color rendering pc-WLED devices.The main research contents of this article are summarized as follows:(1)Aiming at improving the R_a of pc-WLEDs,blue LED chips were coated with Y₃Al₃Ga₂O₁₂:Ce³⁺green phosphor and Ca Al Si N₃:Eu²⁺red phosphor.The broad emission spectrum of the green phosphor compensates for the gap of the cyan-emitting region of470?500 nm and the red phosphor can cover the range of deep red above 650 nm which realizes full-spectrum white-light emission and thus enhances the R_a values of pc-WLEDs.The weight ratio of green/red phosphors was controlled to optimize the optical performances of pc-WLEDs.At the ratio of 0.15/0.012,the fabricated pc-WLED exhibits a natural white light with an ultrahigh R_a of 95.2 and an incredibly small International Commission on Illumination(CIE)chromaticity coordinates deviation(D_uv=-0.0034)at 350 m A.Correspondingly,the CCT and LE values are 4526 K and 62.34 lm/W,respectively.It also exhibits excellent color stability under various bias conditions and maintains stable CCT at around 4500 K and high CRI(R_a=94.8,R₉=88.6,and R₁₃=99)at the current of 1000 m A.(2)Based on the reabsorption effect and the large difference in the luminous efficacy of radiation(LER)between dichromatic phosphors,two separated phosphor configuration structures were constructed for pc-WLEDs by maintaining the same amount of phosphors and silicone as the optimal ratio.The influence of different phosphor configurations on the optical performance of pc-WLEDs was deeply explored.Compared with the R&G mix structure,the R up/G down configuration attains an almost equal R_a,higher LE,and CCT values of 95.8,64.93 lm/W and 5714 K,respectively.It also shows ideal color fidelity(R_f=91)and saturation(R_g=101)under the TM-30-18 standard,which means that it has high color quality under both CRI and TM-30 evaluation standards,and can show high fidelity and almost perfect saturated images.Among them,the LE value increases by 4.2%compared with the R&G mix structure.(3)In order to further improve the LE of pc-WLEDs,a gradient-index structure packaging scheme based on the multivariate nonlinear programming was proposed,and the optimal solution with high and low refractive index of 1.5722 and 1.4 was obtained by optimizing the transmittance.In addition,pc-WLEDs with 1.57R/1.57G sepreated phosphor configuration structure and 1.41R/1.57G gradient-index structure were fabricated,tested and analyzed deeply.Experimental results show that the pc-WLED with 1.41R/1.57G gradient-index structure can not only significantly improve the LE of pc-WLEDs under the premise of guaranteeing high R_a,but also obtain relatively stable luminescence properties.It shows a cool white light with a high R_a of 92.3 and a CCT of 6437 K.Its LE is 72.59lm/W,which is 11.8%higher than 1.41R/1.41G structure and 16.4%higher than 1.41R&G mix structure.