Manganese-activated fluoride phosphors for high-efficacy warm white light-emitting diodes have been limited by low photoluminescence quantum yields. Here, Zhu et al. use an efficient cation exchange reaction to synthesize manganese phosphors with photoluminescence quantum yields as high as 98%.

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Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

Nowadays, phosphor converted white light-emitting diodes (pc-WLEDs) have been widely used in solid-state lighting and display areas due to their superior lifetime, efficiency, and reliability as well as significant reduction in power consumption. Phosphors are indispensable components of pc-WLED devices, and their luminescence properties determine the quality of WLED lighting and displays. In order to further achieve high luminous efficacy, chromatic stability, and color-rending properties in pc-WLEDs, much effort has been focused on improving current pc-WLED phosphors and developing novel pc-WLED phosphors recently. This review article concerns commonly used rare earth ion (Eu2+ and Ce3+) activated inorganic phosphors, highlighting the important effect of spectral tuning via local structural variations on improving the luminescence performance of phosphors. The main spectral tuning strategies are discussed in detail and summarized, including (1) doping level control; (2) cationic substitution; (3) anionic substitution; (4) cationic–anionic substitution; (5) the crystal-site engineering approach; (6) mixing of nanophases.

Recent progress in luminescence tuning of Ce3+ and Eu2+-activated phosphors for pc-WLEDs

Phosphor-converted white light-emitting diodes (pc-WLEDs) are efficient light sources used in lighting, high-tech displays, and electronic devices. One of the most significant challenges of pc-WLEDs is the thermal quenching, in which the phosphor suffers from emission loss with increasing temperature during high-power LED operation. Here, we report a blue-emitting Na3–2xSc2(PO4)3:xEu2+ phosphor (λem = 453 nm) that does not exhibit thermal quenching even up to 200 °C. This phenomenon of zero thermal quenching originates from the ability of the phosphor to compensate the emission losses and therefore sustain the luminescence with increasing temperature. The findings are explained by polymorphic modification and possible energy transfer from electron–hole pairs at the thermally activated defect levels to the Eu2+ 5d-band with increasing temperature. Our results could initiate the exploration of phosphors with zero thermal quenching for high-power LED applications. A blue-emitting phosphor without thermal quenching is reported. The emission losses at high temperatures are compensated by a counter mechanism, originating in energy transfer between electron–hole pairs and thermally activated defect levels.

A zero-thermal-quenching phosphor

Site preferences of dopant Eu2+ on the locations of K+, Ba2+, and Ca2+ in the mixed cation phosphate K2BaCa(PO4)2 (KBCP) are quantitatively analyzed via a combined experimental and theoretical method to develop a blue-emitting phosphor with thermally stable luminescence. Eu2+ ions are located at K2 (M2) and K3 (M3) sites of KBCP, with the latter occupation relatively more stable than the former, corresponding to emissions at 438 and 465 nm, respectively. KBCP:Eu2+ phosphor exhibits highly thermal stable luminescence even up to 200 °C, which is interpreted as due to a balance between thermal ionization and recombination of Eu2+ 5d excited-state centers with the involvement of electrons trapped at crystal defect levels. Our results can initiate more exploration of activator site engineering in phosphors and therefore allow predictive control of photoluminescence tuning and thermally stable luminescence for emerging applications in white LEDs.

Eu2+ Site Preferences in the Mixed Cation K2BaCa(PO4)2 and Thermally Stable Luminescence.

Warm white LEDs with a high color rendering index and a low correlated color temperature have undergone rapid development. In this regard, red-emitting materials-such as fluoride phosphors, namely, A2MF6:Mn(4+) (A = K, Na, and Cs; M = Si, Ge, Zr, Sn, and Ti) and XSiF6:Mn(4+) (X = Ba or Zn), nitridoaluminate phosphor (Sr[LiAl3N4]:Eu(2+)), and nanocrystals of cesium lead iodide perovskite (CsPbI3)-have been extensively investigated recently. These compounds generate narrow emissions in the visible red spectral region that are highly perceived by the human eye and lead to excellent chromatic saturation of the red spectra. This paper describes the structure, luminescence properties, morphologies, thermal features, and moisture resistance of critical red components, as well as their limitations for practical applications. This Perspective also provides a basis for future development and scientific challenges in optical research.

Critical Red Components for Next-Generation White LEDs

The luminous efficiency of white light-emitting diodes, which are used as light sources for next-generation illumination, is continuously improving. Presently available white light-emitting diodes emit with extremely high luminance because their emission areas are much smaller than those of conventional light sources. Consequently, white light-emitting diodes produce a glare that is uncomfortable to the human eye. Here we report a yellow-emitting phosphor, the Eu(2+)-doped chlorometasilicate (Ca(1-x-y,)Sr(x,)Eu(y))(7)(SiO(3))(6)Cl(2), which can be used to create glareless white light-emitting diodes. The (Ca(1-x-y,)Sr(x,)Eu(y))(7)(SiO(3))(6)Cl(2) exhibits a large Stokes shift, efficiently converting violet excitation light to yellow luminescence, and phosphors based on this host material have much less blue absorption than other phosphors. We used crystal structure analysis to determine the origin of the desired luminescence, and we used (Ca(1-x-y,)Sr(x,)Eu(y))(7)(SiO(3))(6)Cl(2) and a blue-emitting phosphor in combination with a violet chip to fabricate glareless white light-emitting diodes that have large emission areas and are suitable for general illumination.

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A novel phosphor for glareless white light-emitting diodes

PROBLEM TO BE SOLVED: To provide a fluorescent substance capable of emitting amber-color light satisfying a desired chromaticity. SOLUTION: The fluorescent substance converting a wavelength of a light emitted from a light emission element to a wavelength exhibiting the amber color, and constituted of a plate-shaped inorganic material is represented by the formula: Ca 3-a-b M a Eu b SiO 4 (Cl 1-c X c ) 2 [wherein, M is at least one kind of elements of Sr and Mg; X is one or more kinds of elements selected from halogen elements except Cl; (a) is a value satisfying 0<a≤2.5; b is a value satisfying 0.002≤b≤0.2; and c is a value satisfying 0≤c≤0.5]. COPYRIGHT: (C)2011,JPO&INPIT

Fluorescent substance, light-emitting module and lighting fixture for vehicle

PROBLEM TO BE SOLVED: To provide a vehicular beacon light using a semiconductor light emitting element, free from fluctuation of light emitting property caused by a temperature of using environment, unnecessary to contrive temperature increase of a light emitting layer of the semiconductor light emitting element. SOLUTION: The vehicular beacon light has a light emitting module 6 constituted of the semiconductor element emitting light of 380 to 420 nm, and a phosphor emitting amber-colored light with the light emitted from the semiconductor light emitting element as an exciting light. As the phosphor, a compound expressed by general formula: Me x Si 12-(m+n) Al (m+n) O n N 16-n :Eu 2+ y is preferable. In general formula, Me is not less than one kind of Li, Ca, Mg, Y, and lanthanide metal excluding La, Ce, and Eu, and x, y, m, and n are positive number respectively. COPYRIGHT: (C)2007,JPO&INPIT

Vehicular beacon light

A phosphor includes a composition represented by the formula: (M2 x, M3 y, M4 z)mM1O3X(2/n), wherein M1 is Si and may include at least one element selected Ge, Ti, Zr, and Sn; M2 is Ca and may include at least one element selected Mg, Ba, and Zn; M3 is Sr and may include at least one element selected from the group consisting of Mg, Ba, and. Zn; X is at least one kind of halogen element; M4 is Eu2+ and may includes at least one element rare-earth elements and Mn, wherein m is in a range of 6/6 ≤ m ≤ 8/6; n is in a range of 5 ≤ n ≤ 7; and x, y, and z satisfies x + y + z = 1, where 0 < x < 1, 0 < y < 1, and 0.01 ≤ z ≤ 0.3.

Europium doped halogen-silicate phosphor and light emitting device

PROBLEM TO BE SOLVED: To provide a blue-light-emitting phosphor and a light emitting module using the same. SOLUTION: The blue-light-emitting phosphor is characterized by being represented by the general formula: Ca 5-X-Y Mg X (PO 4 ) 3 Cl:Eu 2+ Y wherein 0.5≤X≤2.5, 0 COPYRIGHT: (C)2006,JPO&NCIPI

Takeshi Iwasaki

Papers

A novel phosphor for glareless white light-emitting diodes

Fluorescent substance, light-emitting module and lighting fixture for vehicle

Vehicular beacon light

Europium doped halogen-silicate phosphor and light emitting device

Blue-light-emitting phosphor and light-emitting module using the same