Enhancement of optical extraction efficiency in white LED package with quantum dot phosphors and air-gap structure

Shin, Min Ho; Hong, Hyun Guk; Kim, Hyo Jun; Kim, Young Joo

doi:10.7567/apex.7.052101

Cited by 30 publications

(10 citation statements)

References 24 publications

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“…Only those rays with angles of incidence less than 41° could escape the surface, as shown in the schematic of the flat surface in Figure b. Hence, the fraction of the white light escaping the flat surface, f = 0.5 (1 − cos θ c ), was calculated to be only 12.3%; the rest likely underwent TIR and became trapped within the substrate …”

Section: Resultsmentioning

confidence: 99%

Enhanced Luminescence Characteristics of Remote Yellow Silicate Phosphors Printed on Nanoscale Surface‐Roughened Glass Substrates for White Light‐Emitting Diodes

Kim

Eswaran

Kwon

et al. 2016

Advanced Optical Materials

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techniques, [ 6,13,16 ] and new phosphor structures [ 17,18 ] for better performance of white LED structures. However, there have been limited improvements in luminous effi cacy, which still remains a serious challenge hindering commercial success.Trapped loss of light in the air-gap (due to backward photons) and total internal refl ection (TIR) arising within the remote structure are the main factors that critically limit the light extraction. [19][20][21] The reported earlier methods such as scattered photon extraction [ 22 ] and diffused refl ection cup approach [ 23 ] have mainly improved the extraction of back refl ected light. By contrast, few studies to enhance the luminous effi cacy by reducing the TIR in the phosphor part have been reported. Our approach in this study is to adopt a simple nanoscale surface roughening technique to enhance the luminous efficacy by minimizing the TIR at the air-phosphor layer and airglass substrate interface of a remote phosphor LED consisting of yellow phosphor screen-printed on a glass substrate. In the past, surface roughening or surface texturing approaches have been applied to the top n-GaN layer of blue InGaN LED chips to enhance blue light emission by minimizing TIR at the semiconductor-air interface. [24][25][26] Notwithstanding the promising results of surface roughening methods, there have been very limited reports on the deployment of surface texturing techniques for the phosphor layer. One related report is about the random texturing in the case of yttrium aluminum garnet (YAG) phosphor by means of an imprint technique which resulted in an increased luminous fl ux by ≈5.4%. [ 27 ] A patterned YAG phosphor created by pulsed spray coating on a transparent silicone encapsulant resin using a circular mask was reported without increasing the luminous effi cacy. [ 28 ] In this work, we explore a simple surface roughening technique of the glass substrate used as a base for printable remote silicate phosphor, (Ba,Sr,Ca) 2 SiO 4 :Eu 2+ , for the purpose of enhancing the luminescence performance. Compared to other YAG-based phosphors, this yellow silicate phosphor is known to possess higher luminous effi cacy and to have advantages in commercial utilization and cost-effectiveness. We recently reported the utilization of a glass substrate for printable silicate Nonconventional ways to modify phosphor structures have been reported to enhance the overall luminous effi cacy of white light-emitting diodes (LED). Here, a nanoscale texturing technique of a glass substrate with the simple printing process of yellow (Ba,Sr,Ca) 2 SiO 4 :Eu +2 silicate phosphor paste is combined to achieve enhanced white luminescence performance. It is demonstrated that the luminous effi cacy of the resulting printed phosphor layer can be enhanced by ≈16% as a result of controlling surface roughness of the substrate up to 151 nm. The substantial improvement obtained by texturing both sides of the substrate is attributed to the reduction of total internal refl ection of rays at the glass-air interfac...

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Section: Resultsmentioning

confidence: 99%

Enhanced Luminescence Characteristics of Remote Yellow Silicate Phosphors Printed on Nanoscale Surface‐Roughened Glass Substrates for White Light‐Emitting Diodes

Kim

Eswaran

Kwon

et al. 2016

Advanced Optical Materials

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“…If we compare our results to similar works, in [12] they were able to achieve a 10.5% increase of light output power by implementing double layers with different interface shapes in between. While [13] reports that by using a polymer directly lens on the die, and quantum dot phosphor polymer layer distanced from it, a 29.7% increase in efficacy was achieved. And in [14] authors were able to increase the pc-LED's efficacy by 3.27% by forming nanosized moth-eye patterns on the surface of an LED package.…”

Section: Resultsmentioning

confidence: 99%

Remote Pyramid-Shaped Phosphor Coating for Phosphor-Converted White LEDs

Abdullayeva¹,

Orujov²,

Musayeva³

et al. 2017

WJNSE

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Increasing light extraction efficiency is an important task when it comes to manufacturing a powerful white light emitting diode with high luminous flux per watt. In this paper the fabrication of a pyramid-shaped 3-dimensional phosphor coating is reported. It is represented by a phosphor cover, shaped into an array of pyramid like formations. It is proposed that such a structure can improve the light extraction efficiency and the color distribution characteristics of any phosphor-converted white LED. The luminous flux and luminous efficacy are being studied as a function of the forward current across the die. It was found out that with this kind of technique it was possible to achieve an 8% -14% increase in the efficacy of the pc-LED. This increase of light output power is being attributed to the reduction of the phenomena of total internal reflection (TIR) inside the packaging module.

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“…The microlens-attached QD-LEDs have a high luminescence values, which was 1.57 times higher than those of conventional QD-LEDs. Shin et al proposed an air-gap structure to enhance the optical extraction efficiency of QD-LEDs [135]. The proposed structure showed enhancement of 29.7% by experiment as compared with that of a remote layer-by-layer QDs' structure without an air gap.…”

Section: 32mentioning

confidence: 99%

Quantum Dots-Converted Light-Emitting Diodes Packaging for Lighting and Display: Status and Perspectives

Xie

Qiu

Luo

2016

Journal of Electronic Packaging

152

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Recent years, semiconductor quantum dots (QDs) have attracted tremendous attentions for their unique characteristics for solid-state lighting (SSL) and thin-film display applications. The pure and tunable spectra of QDs make it possible to simultaneously achieve excellent color-rendering properties and high luminous efficiency (LE) when combining colloidal QDs with light-emitting diodes (LEDs). Due to its solution-based synthetic route, QDs are impractical for fabrication of LED. QDs have to be incorporated into polymer matrix, and the mixture is dispensed into the LED mold or placed onto the LED to fabricate the QD–LEDs, which is known as the packaging process. In this process, the compatibility of QDs' surface ligands with the polymer matrix should be ensured, otherwise the poor compatibility can lead to agglomeration or surface damage of QDs. Besides, combination of QDs–polymer with LED chip is a key step that converts part of blue light into other wavelengths (WLs) of light, so as to generate white light in the end. Since QD-LEDs consist of three or more kinds of QDs, the spectra distribution should be optimized to achieve a high color-rendering ability. This requires both theoretical spectra optimization and experimental validation. In addition, to prolong the reliability and lifetime of QD-LEDs, QDs have to be protected from oxygen and moisture penetration. And the heat generation inside the package should be well controlled because high temperature results in QDs' thermal quenching, consequently deteriorates QD-LEDs' performance greatly. Overall, QD-LEDs' packaging and applications present the above-mentioned technical challenges. A profound and comprehensive understanding of these problems enables the advancements of QD-LEDs' packaging processes and designs. In this review, we summarized the recent progress in the packaging of QD-LEDs. The wide applications of QD-LEDs in lighting and display were overviewed, followed by the challenges and the corresponding progresses for the QD-LEDs' packaging. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art QD-LEDs' packaging and application technologies.

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Enhancement of optical extraction efficiency in white LED package with quantum dot phosphors and air-gap structure

Cited by 30 publications

References 24 publications

Enhanced Luminescence Characteristics of Remote Yellow Silicate Phosphors Printed on Nanoscale Surface‐Roughened Glass Substrates for White Light‐Emitting Diodes

Enhanced Luminescence Characteristics of Remote Yellow Silicate Phosphors Printed on Nanoscale Surface‐Roughened Glass Substrates for White Light‐Emitting Diodes

Remote Pyramid-Shaped Phosphor Coating for Phosphor-Converted White LEDs

Quantum Dots-Converted Light-Emitting Diodes Packaging for Lighting and Display: Status and Perspectives

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