Nd³⁺‐Doped Silicate Glasses as an Efficient Color Filter to Improve the Color Gamut of a White LED

Abstract

Nd 3+-doped silicate glass (Nd-glass) was employed as a color filter for a white LED based on red and green phosphor (RG-LED), to manipulate the photoluminescence spectral shape and thus to provide a wider color gamut. The hypersensitive transition of Nd 3+ : 4 I 9/2 ? 4 G 5/2 , 2 G 7/2 was adjusted via glass composition and Nd concentration, and improved absorbance as well as reduced the absorption bandwidth. The effective absorption of the Nd-glass at~580 nm reduced the spectral linewidth of the green and red emissions, improving the color reproduction range. The color gamut of the RG-LED was improved from 75.3% to 81.6% NTSC by the introduction of Nd-glass as a color filter. Reliability under high operating current and high temperature were also examined and discussed. K E Y W O R D Sglass, optical materials, photoluminescence, rare earths, silicates | INTRODUCTIONLiquid crystal displays (LCD) require a white back light unit (BLU) with a proper spectral combination of blue, green, and red emission for color reproduction. A white light emitting diode composed of red and green phosphors with a blue LED chip (RG-LED) has been widely used for the LCD-BLU light source.1-3 Since a wide color gamut can be achieved using primary colors 4 and the well-matched spectrum of the white LED (wLED) to the red, green, and blue (RGB) color filters of LCDs, 2 the broad spectral bandwidths of green and red emissions from the phosphors practically restricts the potential color reproduction range of the resultant LCD. In contrast, quantum dots (QDs) exhibit a narrow spectral bandwidth at the designated green and red emission peaks due to their characteristic exciton transitions, and thus have recently begun to be applied to highquality LCDs with wide color gamut. 5,6 However, QDs require hermetic passivation layers to protect them from degradation resulting from interaction with the atmosphere 6 and they have a higher production cost than conventional wLEDs. Thus, for cost-effective production of high-quality LCDs, it is highly desirable for conventional RG-LEDs to have the proper spectral shape. The visible emission spectra of RG-LEDs can be manipulated if the proper color filter can be introduced. Nd 3+ has strong absorption due to the 4 I 9/2 ? 4 G 5/2 , 2 G 7/2 transition, which is mostly centered at~580 nm, and can effectively modify the photoluminescence (PL) spectra of the RG-LED. Thus, a silicate glass doped with Nd 3+ can be a good color filter for spectral shape adjustment. As schematically drawn in Figure 1, a new configuration of RG-LED can be proposed using Nd 3+ -doped glass (Nd-glass), which absorbs the orange emission band and thus narrows the emission bandwidth of the green and red PL spectra from the currently employed phosphors. The Nd 3+ : 4 I 9/2 ? 4 G 5/2 , 2 G 7/2 transition is a characteristic hypersensitive transition, which is highly sensitive to changes in the local structure involving the Nd 3+-ion, such as the coordination number, bond strength, covalency, and symmetry of the crystalline field...

Cd–S–Se quantum dot embedded glasses with dual emissions for wide color gamut white LED

“…When compared to a commercial wLED used for an LCD backlight and composed of red and green phosphors (RG‐LED), with a 75% NTSC color gamut, 28,29 the Cd‐S‐Se QDEG performance confirmed it was suitable for LCD displays with conventional picture quality. Because conventional RG‐LEDs employ organic resins with weak chemical and thermal durability, they have relatively weak long‐term stability.…”

Review—A Review on Phosphor in Glass as a High Power LED Color Converter

“…Thus, the spectrum match of the wLED with color filters determines the R, G, B colors, but the broad emission bandwidth of the conventional wLED, which uses green and red phosphors embedded in silicone resin (RG-LED), restricts the color reproduction range (color gamut) at ∼75% to that of the range defined by the national television standard committee (NTSC). 162 Han et al thus employed a Nd 3+ -doped glass on top of the conventional RG-LED to modify the emission bandwidth via a strong 4f-4f transition of Nd 3+ : 4 I 9/2 → 4 G 5/2 , 2 G 7/2 and successfully expanded the color gamut up to ∼ 82% of the NTSC standard. 162 As the previous work used silicone resin with inherent weak long-term stability, Lee et al doped the silicate glass with the Nd 3+ -ion and fabricated a PiG with LuAG:Ce 3+ (green) and CASN:Eu 2+ (red) phosphors.…”

“…162 Han et al thus employed a Nd 3+ -doped glass on top of the conventional RG-LED to modify the emission bandwidth via a strong 4f-4f transition of Nd 3+ : 4 I 9/2 → 4 G 5/2 , 2 G 7/2 and successfully expanded the color gamut up to ∼ 82% of the NTSC standard. 162 As the previous work used silicone resin with inherent weak long-term stability, Lee et al doped the silicate glass with the Nd 3+ -ion and fabricated a PiG with LuAG:Ce 3+ (green) and CASN:Eu 2+ (red) phosphors. 163 As shown in Fig.…”

Double Encapsulation of CsPbBr3 Perovskite Nanocrystals with Inorganic Glasses for Robust Color Converters with Wide Color Gamut

“…Phosphor-in-glass (PiG) has been proposed as a robust color converter for a white light emitting diode (wLED) with improved long-term stability, since it is a simple mixture of a transparent inorganic glass matrix with dispersed ceramic phosphor powders. − Its features include the easy manipulation of color conversion properties, which can be simply accomplished by varying the mixing ratio of phosphor and glass frit. PiGs have been recently commercialized in high power white LED applications and have shown excellent thermal and chemical stability. − However, the broad emission bandwidth of commercial ceramic phosphors restricts the color reproduction range (or color gamut) when they were used as a light source for display applications such as liquid crystal displays (LCDs). − …”