Critical Review—Narrow-Band Nitride Phosphors for Wide Color-Gamut White LED Backlighting

Abstract

To achieve a brilliant image with high color saturation in white LED backlighting technology, innovative phosphor materials with narrow-band emission in the green and red spectral region are continuously pursed. Nitride phosphors are so far accepted as the most suitable phosphors for white LED backlights due to their high efficiency and excellent robustness. In this perspective, we will present an overview about the recent developments of state-of-the-art and newly-emerging nitride phosphors with a narrow emission band, and the emphasis would be placed on the relationships between the crystal structure and luminescence properties. Finally, some empirical rules for designing novel narrow-band phosphors for backlighting technologies would be summarized. Nowadays, liquid crystal displays (LCDs) are ubiquitous in our daily lives, and their applications range from smartphones, tablets, computers, to large-screen TVs, and data projectors. As there is much concern on backlight units with larger color gamut, higher brightness, lower power consumption and mercury-free, white light-emitting diodes (LEDs) have been widely applied as backlighting components in modern LCD technologies to replace the traditional cold cathodefluorescence lamps (CCFLs). 1-12Multi-chip white LEDs, which comprise red-, green-and blueemitting chips, exhibit excellent color performance and tuning abilities. However, the efficiencies of red, green, and blue LEDs vary overtime at different rates. In addition, separated driving circuits and complicated feedback-driven systems are required, which leads to a high cost. Moreover, the efficiency of green LEDs, known as "green gap", is much smaller than that of red and blue ones.13-15 By contrast, phosphor-converted (pc) white LED backlights, which combine a single LED chip with phosphor materials, are mostly used due to their high efficiency, cost effectiveness and robustness. To achieve a large color gamut and to faithfully reproduce the natural colors, the emission peak of phosphors should match well with the RGB color filters of LCDs. Phosphors with narrow emission bands would loss less their luminescence after passing through color filters, and also promise high color purity. Therefore, narrow-band phosphors with appropriate emission maximum are required for high efficiency and wide color gamut backlights. 13,15 Quantum dots (QDs) materials have shown great potentials for next-generation displays due to their narrow emission band. [7][8][9][10][11][12] In comparison to traditional CCFL having a color gamut of ∼75% of the National Television Standard Committee (NTSC) standard, the Cdcontaining QDs-integrated white LED backlights promise a large color gamut of > 100% NTSC, but the application has been limited due to the usage restrictions of hazardous Cd compounds. Compared to Cdcontaining rivals, the non-toxic InP/ZnS QDs only yield a color gamut of 87% NTSC due to the quite broader emission band.11 Moreover, it is difficult to maintain the initial optical properties of the QDs during device fabricatio...

RbKLi2[Li3SiO4]4:Eu2+ an ultra narrow-band phosphor

“…The goal is to improve the color gamut in order to realize the most lifelike artificial display. This can only be achieved by developing and combining phosphors with the desired peak positions, narrow emission bands, and high quantum efficiencies [14][15][16].…”

Local coordination, electronic structure, and thermal quenching of Ce3+ in isostructural Sr2GdAlO5 and Sr3AlO4F phosphors

“…Phosphors employed in light emitting diode (LED) or laser diode (LD) pumped white lighting highly rely on Ce 3+ /Eu 2+ activators’ parity‐ and spin‐allowed d ‐ f transitions, which permits broad band feature of photoluminescence excitation and emission . The lifetime of the Ce 3+ /Eu 2+ 5 d →4 f transition is usually in the range of 30‐60 ns and 0.6‐1.0 μs, respectively.…”

Facile synthesis of the desired red phosphor Li2Ca2Mg2Si2N6:Eu2+ for high CRI white LEDs and plant growth LED device

“…Differencing from Eu 2+ ions in a highly symmetric cuboid like environment of SrLiAl 3 N 4 or in highly unusual EuN 9 coordination polyhedron of β‐SiAlON, this compound with distorted octahedral coordination for Eu 2+ still shows relative narrow band. The possible reason is that the lattice ions like Li, Mg, and Si occupy distinct lattice sites instead of the same lattice site with a statistical distribution, inducing small Stokes shifts and restricting inhomogeneous emission band broadening, thus narrow band occurs . The room‐temperature decay curve of Li 2 Ca 2 Mg 2 Si 2 N 6 :1.0%Eu 2+ phosphor under excitation at 460 nm, monitored at the peak of 648 nm is shown in Figure B.…”

“…The possible reason is that the lattice ions like Li, Mg, and Si occupy distinct lattice sites instead of the same lattice site with a statistical distribution, inducing small Stokes shifts and restricting inhomogeneous emission band broadening, thus narrow band occurs. 24,26 The room-temperature decay curve of Li 2 Ca 2 Mg 2 Si 2 N 6 :1.0%Eu 2+ phosphor under excitation at 460 nm, monitored at the peak of 648 nm is shown in Figure 3B. The lifetime of Li 2 Ca 2 Mg 2 Si 2 N 6 :1.0%Eu 2+ was calculated to be 0.7 μs, which is in line with those determined for other Eu 2+ -doped nitridosilicate red phosphors, such as (Ca/Sr)AlSiN 3 :Eu 2+ (τ = 0.6-0.8 μs) and SrLiAl 3 N 4 :Eu 2+ (τ = 0.6 μs).…”