This study introduces quantum dot (QD)-based polarized white light-emitting diodes (W-LEDs) combined with a shortwavelength pass dichroic filter (SPDF), which transmit blue wavelength regions and reflect yellow wavelength regions, and a reflective polarizer film (RPF)-sandwiched AgIn5S8-ZnS QD layer using an electrospray (e-spray) method. The AgIn5S8-ZnS QDs are good candidates for W-LEDs because of their broad emission band (~100 nm) from the donoracceptor emission. The yellow emitting AgIn5S8-ZnS QDs are synthesized using a colloidal hot injection method and mixed with dimethylformamide (DMF), toluene, and poly(methyl methacrylate) (PMMA) for e-spray coating on glass. Furthermore, SPDFs are used instead of glass substrates to enhance the yellow emission from the QD layer. To create the polarized light, the RPF is fabricated on QD-coated glass and SPDFs. To create white light, a blue LED chip (λmax = 450 nm) is used as the blue light source and an excitation source for the yellow QD film with an applied current of 60 mA. The electroluminescence (EL) intensity with an angular orientation of the polarizer is measured as a function of the polarizer-rotating angle from −90° to 90° at 10° intervals.
This paper introduces high color rendering index (CRI) white light-emitting diodes (W-LEDs) coated with red emitting (Sr,Ca)AlSiN3:Eu phosphors and yellowish-green emitting AgIn5S8/ZnS (AIS/ZS) quantum dots (QDs) on glass or a short-wavelength pass dichroic filter (SPDF), which transmit blue wavelength regions and reflect yellow wavelength regions. The red emitting (Sr,Ca)AlSiN3:Eu phosphor film is coated on glass and a SPDF using a screen printing method, and then the yellowish-green emitting AIS/ZS QDs are coated on the red phosphor (Sr,Ca)AlSiN3:Eu film-coated glass and SPDF using the electrospray (e-spray) method.To fabricate the red phosphor film, the optimum amount of phosphor is dispersed in a silicon binder to form a red phosphor paste. The AIS/ZS QDs are mixed with dimethylformamide (DMF), toluene, and poly(methyl methacrylate) (PMMA) for the e-spray coating. The substrates are spin-coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to fabricate a conductive surface. The CRI of the white LEDs is improved through inserting the red phosphor film between the QD layer and the glass substrate. Furthermore, the light intensities of the multi-layered phosphor films are enhanced through changing the glass substrate to the SPDF. The correlated color temperatures (CCTs) vary as a function of the phosphor concentration in the phosphor paste. The optical properties of the yellowish-green AIS/ZS QDs and red (Sr,Ca)AlSiN3:Eu phosphors are characterized using photoluminescence (PL), and the multi-layered QD-phosphor films are measured using electroluminescence (EL) with an InGaN blue LED (λmax = 450 nm) at 60 mA.
In this study, several combinations of multi-package white light-emitting diodes (LEDs), which combine an InGaN blue
LED with green, amber, and red phosphor-converted LEDs (pc-LEDs), were characterized by changing the peak
wavelength of green pc-LEDs between 515nm and 560nm (515, 521, 530, 540, 550, 560nm) in color temperature of
6,500K and 3,500K. Various green monochromatic pc-LEDs were fabricated by capping a long-wave pass-filter (LWPF)
on top of pc-LEDs to improve luminous efficacy and color purity. LWPF-capped green monochromatic pc-LED can
address the drawback of green semiconductor-type III-V LED, such as low luminous efficacy in the region of green gap
wavelength. Luminous efficacy and color rendering index (CRI) of multi-package white LEDs are compared with
changing the driving current of individual LED in various multi-package white LEDs. This study provides a best
combination of four-color multi-package white LEDs which has high luminous efficacy and good CRI.
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