量子點白光LED光譜擬合方法的研究

劉遠海，劉 文*，何思宇，蔣福春，柴廣躍,，張 旺

量子點白光LED光譜擬合方法的研究

劉遠海1，劉 文1*，何思宇1，蔣福春1，柴廣躍1,2，張 旺2

1深圳大學光電工程學院，廣東 深圳 518061；2深圳技術(shù)大學新能源與新材料學院，廣東 深圳 518118

量子點材料具有發(fā)光光譜窄、發(fā)光波長可調(diào)及熒光量子產(chǎn)率高等特點，其制成的發(fā)光器件在提升色域方面更具潛力。本文介紹了一種由藍光LED激發(fā)CdSe紅、綠光量子點并結(jié)合表色系統(tǒng)計算方法配得白光的計算方法。經(jīng)多次實驗確定，紅、綠光量子點與膠水配比為(1∶60)和(1∶10)，膠量測試范圍為1.4 μL～2.2 μL和3.0 μL～5.0 μL。采用傳統(tǒng)LED制作方式和分層結(jié)構(gòu)制得樣品，測試此膠量范圍對藍光的吸收、轉(zhuǎn)化比率，經(jīng)Matlab擬合得到膠量與吸收、轉(zhuǎn)化率的函數(shù)關(guān)系。取上述測試膠量范圍形成的白光區(qū)域點(0.34，0.3)，得到紅、綠光量子點膠量為1.9 μL和4.55 μL，根據(jù)光譜計算公式得到對應(yīng)的理論光譜。再根據(jù)上述膠量制作驗證樣品，測試得到色坐標點為(0.3409, 0.2992)且對應(yīng)的光譜與理論光譜也基本重合。

量子點；白光LED；Matlab；光譜擬合

1 引 言

21世紀是一個信息與顯示時代，顯示技術(shù)無處不在，如智能手機、電腦等都與顯示技術(shù)息息相關(guān)[1]。目前，用做顯示背光源的白光LED主要由藍光LED芯片與一種或多種熒光粉組合而成，芯片發(fā)出的藍光與激發(fā)熒光粉獲得的黃光混合得到白光[2]。顯示應(yīng)用希望擁有高顏色飽和度，用于白光LED的熒光粉(如YAG: Ce+)大都具有較寬的發(fā)射光譜，而減小發(fā)射光譜帶寬能夠增大顯示器色域、提高飽和度。因此，窄光譜發(fā)射的熒光材料成為背光領(lǐng)域研究熱點[3]。

量子點是指在空間三個維度上存在量子限域效應(yīng)的半導體晶體材料，又被稱為“人造原子”[4-5]。與傳統(tǒng)熒光粉相比，半導體量子點作為一種新型波長轉(zhuǎn)換材料具有發(fā)射光譜窄[6]、量子產(chǎn)率高、容易與器件集成等優(yōu)良特性[7-8]，并且可以通過改變尺寸來調(diào)控其光學和電學性質(zhì)[9-11]。量子點背光因其RGB三色的半峰寬窄，色純度高，因而可以實現(xiàn)更高的色域，可以實現(xiàn)NTSC110%的色域[12]。近期，南京理工大學學報報道了使用綠色和紅色CsPbX3 PeQDs/PMMA薄膜作為熒光轉(zhuǎn)換材料的白光LED器件，得到的色域顯著大于NTSC的標準色域[13-14]。韓國學者報道了藍光LED激發(fā)5種顏色無機鈣鈦礦量子點的白光LED，色域達到了NTSC標準色域的145%[15]。

目前，針對光譜疊加的研究較多，如通過光功率譜的配比得到高顯色性白光[16]，但未結(jié)合實際生產(chǎn)中熒光粉質(zhì)量比加以驗證。本文利用藍光激發(fā)CdSe紅光和綠光量子點得到白光，測得不同量的量子點對應(yīng)的光功率譜，通過Matlab擬合出紅、綠光量子點膠體用量與吸收率、轉(zhuǎn)化率關(guān)系式，利用光譜疊加原理擬合出白光，經(jīng)實際配量測出的光譜與理論光譜基本一致，這對于今后的實際配粉工作具有一定指導作用。

2 實驗原理與過程

2.1 實驗原理

量子點光致發(fā)光原理[16]是量子點材料吸收光子后電子躍遷產(chǎn)生新的光子。材料在吸收光子后產(chǎn)生輻射復合與非輻射復合兩個過程，新的光子產(chǎn)生于輻射復合過程，故新光子存在一定的轉(zhuǎn)化效率。本實驗將量子點與膠水的混合物作為研究對象，故考慮利用量子點膠體對藍光的吸收率與其轉(zhuǎn)化成紅、綠光的轉(zhuǎn)化率進行光譜計算。

實驗樣品結(jié)構(gòu)如圖1所示，測試得到紅、綠光量子點膠量對藍光的吸收率及轉(zhuǎn)化率，通過Matlab計算擬合吸收、轉(zhuǎn)化率與膠量的最優(yōu)函數(shù)關(guān)系式。紅綠藍三色光的光功率計算方法如式(1)~式(3)所示：

其中：2為紅光光功率，0為藍光初始光功率，0為紅光量子點吸收率，0為紅光量子點轉(zhuǎn)化率；4為綠光光功率，1為綠光量子點吸收率，1為綠光量子點轉(zhuǎn)化率；3為藍光所剩光功率。白光絕對光譜計算方法如式(4)所示：

其中：P(λ)為白光絕對光譜，P1(λ)為藍光相對光譜，P2(λ)為紅光相對光譜，P3(λ)為綠光相對光譜。

由白光光譜()得到對應(yīng)的色坐標點，則需要引入國際照明委員(CIE)1931 XYZ表色系統(tǒng)計算方法[17]：

其中：，，為色坐標，為人眼對于紅、綠、藍色感知強度，它們分別為

其中：()光源光譜功率分布，()、()、()為顏色匹配函數(shù)，為調(diào)整系數(shù)。

2.2 實驗過程

1) LED芯片與支架焊接，并打線。

2) 分別測得藍光LED芯片、紅、綠光量子點的相對光譜：1()、2()、3()。

3) 測出藍光芯片初始光功率為0。

4) 量子點與環(huán)氧按比例混合均勻，在藍光芯片上利用點膠機點入一層紅光量子點膠體(膠量：)，計算擬合得到紅光量子點對藍光的吸收率函數(shù)0=R1()，轉(zhuǎn)化率函數(shù)0=R2()。

5) 同步驟4)計算擬合得到綠光量子點(膠量：)對藍光的吸收率函數(shù)1=G1()，轉(zhuǎn)化率函數(shù)1=G2()。

6) 根據(jù)式(1)～式(4)計算出白光絕對光譜。

7) 再由白光光譜及式(5)～式(12)計算出色坐標點。

3 實驗結(jié)果及數(shù)據(jù)分析

3.1 實驗步驟

分別測得LED芯片、紅光量子點和綠光量子點的相對光譜，如圖2所示。

經(jīng)多次實驗確定紅光量子點與膠水配比(1:60)，綠光量子點與膠水配比(1:10)，按照表1所示膠量，將膠體量子點點入LED杯碗(型號2835)中，固化、恒流測量光功率，得到吸收率和轉(zhuǎn)化率如表1所示。

通過Matlab曲線擬合得到紅、綠光量子點吸收和轉(zhuǎn)化率曲線，如圖3所示。

圖3(a)曲線得到紅光量子點吸收率函數(shù)：

R1()=-0.06212+0.3012+0.2405；

圖3(b)曲線得到紅光量子點轉(zhuǎn)化率數(shù)：

R2()=-0.19393+1.0182-1.6786+1.0576；

圖3(c)曲線得到綠光量子點吸收率函數(shù)：

G1()=-0.00742+0.1046+0.4863；

圖2 (a) 藍光芯片相對光譜；(b) 綠光量子點相對光譜；(c) 紅光量子點相對光譜

表1 不同量子點膠量的吸收和轉(zhuǎn)化率

圖3 (a) 紅光量子點吸收率擬合曲線；(b) 紅光量子點轉(zhuǎn)化率擬合曲線；(c) 綠光量子點吸收率擬合曲線；(d) 綠光量子點轉(zhuǎn)化率擬合曲線

圖3(d)曲線得到綠光量子點轉(zhuǎn)化率數(shù)：

G2()=-0.01264+0.212813-1.33682+3.6827-3.5381。

取紅、綠光量子點膠量最大、最小值的4種組合計算得到對應(yīng)的吸收、轉(zhuǎn)化率，再由式(1)～式(4)計算出光譜，將光譜帶入式(5)～式(12)計算得到邊界點的色坐標值：2(0.4006，0.3009)，2(0.3327，0.3102)，3(0.3027，0.2508)，4(0.3661，0.2603)，得到色坐標計算區(qū)域如圖4所示。

圖4 色坐標計算區(qū)域

驗證理論計算的準確性，取色坐標為(0.34，0.3)，利用色坐標計算式(5)~式(12)及紅、綠光量子點吸收、轉(zhuǎn)化函數(shù)反推得到紅、綠光量子點膠量分別為1.52 μL和4.65 μL，得到預測光譜與實際光譜如圖5所示。理論計算與實際光譜偏差太大，考慮以下兩種原因引起誤差：一是在制作測試樣品過程中紅光量子點經(jīng)過兩次加熱，引起量子點缺陷暴露，導致光譜誤差較大，二是不同膠量對于出光的影響。

圖5 預測光譜與實際光譜

3.2 實驗誤差驗證分析

驗證紅光量子點加熱兩次損失情況：通過在烘箱里加熱，對比一次加熱和兩次加熱的紅光光功率，如圖6(a)所示，發(fā)現(xiàn)紅光光功率衰減約5%，可認為上述誤差不是由紅光量子點二次加溫導致的。

本模型計算中將彈體假定為球形彈，將上述參數(shù)代入式(41)和式(43)得到，vr為599 m·s-1，vh 為1 503 m·s-1，這些理論計算值與實驗觀察結(jié)果[9]一致。當彈體以較高沖擊速度侵徹混凝土靶板時，由于燒蝕和磨損效應(yīng)會造成一些質(zhì)量損失，這將在以后的工作中予以考慮。

驗證不同膠量對于出光的影響：經(jīng)光學顯微鏡觀察不同樣品發(fā)現(xiàn)，膠量少時樣品表面形成凹面，膠量多時樣品表面形成凸面，結(jié)構(gòu)如圖6(b)所示。取兩個不同白膠膠量分別制得凹凸面樣品，測試結(jié)果如圖6(c)所示。分析原因為：藍光經(jīng)過凹表面時易發(fā)生全反射，藍光出光減少，紅光量子點吸收的藍光增加；藍光經(jīng)過凸表面時減少全反射發(fā)生，藍光出光增加，紅光量子點吸收的藍光減少。因此，實驗過程中需要考慮紅光量子點膠量與綠光量子點膠量的相互影響。

3.3 改進過程及結(jié)果

之前實驗分析僅以紅、綠光量子點的量作為自變量來計算獲得紅、綠量子點吸收、轉(zhuǎn)化率。但實驗發(fā)現(xiàn)膠水量對于出光也有較大影響，故而改進實驗將紅、綠光量子點的量和白膠膠量作為自變量來擬合紅、綠光量子點的吸收、轉(zhuǎn)化率。采用一種量子點膠量對應(yīng)五種白膠膠量的方法，制得樣品并測試得到吸收、轉(zhuǎn)化率與膠量的關(guān)系如圖7所示。

圖6 (a) 紅光量子點兩次加熱影響；(b) 凹、凸面樣品示意圖；(c) 凹凸面對于藍光出光影響

圖7 (a) 紅光量子點吸收率擬合曲面；(b) 紅光量子點轉(zhuǎn)換率率擬合曲面； (c) 綠光量子點吸收率擬合曲面；(d) 綠光量子點轉(zhuǎn)換率率擬合曲面

圖7(a)曲面為紅光量子點吸收率函數(shù)：

R1(,)=1.3211-0.3534-0.3059
+0.07032+0.0637+0.01772；

圖7(b)曲面為紅光量子點轉(zhuǎn)換率函數(shù)：

R2(,)=-1.4401-15.0701+9.4111

+13.96012-1.8301-3.3142-4.96413
-0.01012+0.50382+0.49713+0.63754

+0.04323-0.031822-0.03433-0.02784；

圖7(c)曲面為綠光量子點吸收率函數(shù)：

G1(,)=0.5188+0.1145-0.0457-0.01012-0.01012；

圖7(d)曲面為綠光量子點轉(zhuǎn)化率函數(shù)：

G2(,)=-20.8501+14.8101+15.9401

-5.22212-2.1771-11.24012+0.84653

+0.25012+0.64392+3.79213-0.05014

-0.00423-0.053622-0.04013-0.51314。

取紅、綠光量子點膠量最大、最小值的4種組合計算得到對應(yīng)的吸收、轉(zhuǎn)化率，再由式(1)～式(4)計算出光譜，將光譜帶入式(5)～式(12)計算得到邊界點的色坐標值：1(0.3648，0.3003)，2(0.3327，0.3102)，3(0.3203，0.2719)，4(0.3637，0.2662)，得到色坐標計算區(qū)域如圖8所示。

圖8 色坐標計算區(qū)域

圖9 (a) 預測與實際光譜；(b) 預測與實際色坐標點；(c) 樣品點亮前后效果圖

4 總結(jié)與展望

本文采用藍光激發(fā)CdSe紅、綠光量子點制得量子點白光LED。通過理論計算出白光光譜，結(jié)合量子點配粉驗證光譜，確定出白光光譜與實際量子點粉及膠量之間的函數(shù)關(guān)系，最終得到理論光譜與實際光譜基本一致。本文只考慮白光光譜擬合的一致性，而未考慮最終樣品的光效、顯色指數(shù)及色溫等性能參數(shù)，所以后續(xù)實驗將繼續(xù)深入研究。

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Study on spectral fitting method of quantum dot white LED

Liu Yuanhai1, Liu Wen1*, He Siyu1, Jiang Fuchun1, Chai Guangyue1,2, Zhang Wang2

1College of Photoelectric Engineering, Shenzhen University, Shenzhen, Guangdong 518061, China;2College of New Energy and New Materials, Shenzhen Technology University, Shenzhen, Guangdong 518118, China

Prediction and actual spectrum

Overview:Quantum dot material is a new semiconductor luminescent material which has the characteristics of narrow luminescent spectrum, adjustable luminescent wavelength and high quantum yield. Because of its narrow fluorescence spectrum, the light-emitting device is very helpful to improve the color gamut and saturation in the backlight field. Quantum dot materials are used as backlight devices to improve the color gamut and saturation which need to match the white light to meet the requirements through the principle of three primary colors. At present, there are many studies on the fitting method of white light spectrum, but it is not verified by the quality ratio of fluorescent materials in actual production. Based on the CIE 1931 XYZ surface color system, a new white light spectrum fitting method is developed in this paper.

The ratio of red and green QDs to glue was (1: 60) and (1: 10). The test range of the glue content was 1.4 μL~2.2 μL and 3.0 μL~5.0 μL. In the experiment, the traditional LED manufacturing method is used and the red green quantum dots are excited by the characteristics of blue light short wavelength and high energy to obtain the red green blue three colors which are mixed into white light. At the same time, due to the more stable nature of red quantum dots, the layered structure of red quantum dots under green quantum dots is adopted. Make samples according to the above-mentioned manufacturing method, test the absorption and conversion ratio of different samples to blue light, get the functional relationship between glue amount and absorption and conversion ratio through Matlab fitting, and then substitute it into the calculation formula to get the white light area. In the experiment, it is found that the amount of red-green quantum dots with layered structure will affect each other's absorption conversion; therefore, when fitting the functional relationship between the amount of glue and the absorption conversion, it is necessary to take the amount of red-green quantum dots as an independent variable at the same time.

According to the spectral fitting method, the white light region of each sample in the color coordinate is calculated, and a point (0.34, 0.3) in the region is taken. The corresponding red and green quantum dots are 1.9 μL and 4.55 μL by the inverse use of the spectral fitting method, so the corresponding theoretical spectrum is obtained. Then, according to the above-mentioned amount of glue, the white light spectrum is obtained, which basically coincides with the theoretical spectrum, and the color coordinate points (0.3409, 0.2992) obtained from the actual spectrum are also basically close. The fitting method of white light spectrum introduced in this paper is combined with the actual production and verified, which has a certain reference value for the preparation of white light of photoluminescent products.

Citation: Liu Y H, Liu W, He S Y,Study on spectral fitting method of quantum dot white LED[J]., 2020, 47(6): 190288

Study on spectral fitting method of quantum dot white LED

Liu Yuanhai1, Liu Wen1*, He Siyu1, Jiang Fuchun1, Chai Guangyue1,2, Zhang Wang2

1College of Photoelectric Engineering, Shenzhen University, Shenzhen, Guangdong 518061, China;2College of New Energy and New Materials, Shenzhen Technology University, Shenzhen, Guangdong 518118, China

Quantum dot materials have the characteristics of narrow luminescence spectrum, adjustable luminescence wavelength and high fluorescence quantum yield. The quantum dot LEDs have more potential in improving color gamut. In this paper, a method of white light generation by blue LED excited CdSe red and green quantum dots is introduced. The ratio of red and green quantum dots to glue was (1∶60) and (1∶10), and the test range of glue content was 1.4 μL～2.2 μL and 3.0 μL～5.0 μL. The samples were prepared by traditional method and layered structure. The absorption and conversion ratio of blue light in the range of glue amount were tested. The function relationship between glue amount and absorption and conversion was obtained by Matlab fitting. When taking the dots (0.34, 0.3) in white light region formed in the above test glue amount range, the red and green quantum dots were calculated with glue amount of 1.9 μL and 4.55 μL, and the corresponding theoretical spectrum was established according to the spectral calculation formula. According to the above glueamount, the verificationsamples were madeand tested the color coordinates (0.3409, 0.2992) and the homologousspectra were basically coincident with the theoretical spectra.

quantum dots; white LED; Matlab; spectral fitting

O433.4

A

10.12086/oee.2020.190288

: Liu Y H, Liu W, He S Y,. Study on spectral fitting method of quantum dot white LED[J]., 2020,47(6): 190288

劉遠海，劉文，何思宇，等. 量子點白光LED光譜擬合方法的研究[J]. 光電工程，2020，47(6): 190288

Supported by National Fund Committee-Shenzhen Unite Fund Key Support Project (U1613212)

* E-mail: liuwen@szu.edu.cn

2019-05-29；

2019-12-24

國家基金委—深圳市聯(lián)合基金重點支持資助項目(U1613212)

劉遠海(1993-)，男，碩士，主要從事光器件封裝的研究。E-mail：yuanhailiu0489@163.com

劉文(1968-)，男，博士，副教授，主要從事半導體工藝及應(yīng)用技術(shù)的研究。E-mail：liuwen@szu.edu.cn