Polychromatic light-emitting diodes with a fluorescent nanosphere opal coating

Abstract

A hexagonally close-packed array consisting of fluorescent nanospheres was coated onto short-wavelength GaN light-emitting diodes to demonstrate polychromatic white light emission. The spherical particles self-assemble into ordered three-dimensional opal structures, performing the role of color conversion to generate a polychromatic spectrum with smooth and uniform emission patterns. Different ratios of green and orange-red fluorescent nanospheres were mixed and coated onto high-extraction-efficiency micro-LEDs. Four devices with different shades of white emission were demonstrated. Device A, with a high content of orange-red nanospheres, offers the highest CRI value of 80, whereas device C with a well-balanced ratio of green and orange-red nanospheres exhibits color characteristics closest to ideal white with CIE coordinate at (0.34, 0.34). At 20 mA driving current, the luminous efficacy of the devices A, B, C, and D are 40.5 lm W(-1), 57.7 lm W(-1), 63.1 lm W(-1), and 67.2 lm W(-1) respectively, while the correlated color temperatures (CCTs) of the corresponding devices are 3587, 4778, 5271, and 13 000 K.

Long-living and highly efficient bio-hybrid light-emitting diodes with zero-thermal-quenching biophosphors

“…These concerns have fueled the renaissance of hybrid LEDs (HLEDs) [13][14][15] . In these devices, the IPs are replaced by organic phosphors (OPs) ranging from polymer matrices doped with artificial emitters [16][17][18] , over luminescent metal organic frameworks (MOFs) [19][20][21] , to biophosphors based on either DNA/protein matrices to host artificial emitters 15,[22][23][24][25][26] or fluorescent proteins (FPs) embedded in polymer/MOF matrices or alone 15,[27][28][29][30][31][32][33][34] . Like IPs, OPs must exhibit a narrow emission with high photoluminescence quantum yields (ϕ), high molar extinction coefficients (ε), outstanding photobleaching stabilities under operating conditions, and low heat generation and thermal quenching upon continuous excitation.…”

“…These limitations have brought biophosphors into focus, leading to Bio-HLEDs featuring performances close to those with Ir-based OPs 15,[27][28][29][30][31][32][33][34] . Here, FP-phosphors stand out, since (i) the photoluminescence features of FPs fulfills all of the above requirements 27 , (ii) the protein backbone is an effective shield against ambient oxygen 40,41 , and (iii) FPs production can be carried out in a cheap and sustainable way using bacteria (please notice that lighting and laser applications do not require high purification levels).…”

“…The most critical aspect in the development of proteinphosphors is how to stabilize FPs out of aqueous solutions and physiological environments, preserving their bio-functionality over long periods of time. Although the idea of using FPs in lighting was proposed in 2000 42 , to date only three approaches have successfully realized FP-based Bio-HLEDs, namely (i) dry films prepared in a glass reservoir with a high concentration of FPs 32 , (ii) FPs encapsulated into MOFs 33 , and (iii) FP-polymer elastomeric coatings-i.e., a mixture of star-like hydrophilic polymer trimethylolpropane ethoxylate (TMPE) to stabilize the FPs and a linear polyethylene oxide polymer acting as a jellification agent [27][28][29][30][31][32][33][34] . The latter has provided the best performing devices with stabilities of <300 h 28,30 and <5 min 31 at low-and high-applied currents, respectively.…”

Nanosphere Lithography for Nitride Semiconductors

“…Figure 9 shows PL spectra and optical images of fluorescent nanosphere on GaN LEDs with blue emission as in the studies by K.N. Hui et al (Hui et al, 2008). With different colors of fluorescent nanospheres, including green, yellow and red, emission spectrum of LEDs can be tuned to different shades of white light.…”

Angularly Uniform White Light-Emitting Diodes Using an Integrated Reflector Cup

“…The excitation blue InGaN-GaN LED was fabricated by standard microfabrication techniques, details of which can be found in references such as [5]. The wafers were then thinned down to 150 m. The process begins to differ from the conventional flow at the step of wafer dicing.…”