A Zero-Thermal-Quenching Blue Phosphor for Sustainable and Human-Centric WLED Lighting

Abstract

The worldwide popularization of white-light-emitting diode (WLED) lighting brings about chronic blue-light exposure, which has severe negative impacts on human health and circadian rhythm. The blue-light hazard can be readily minimized by developing violet LED chip (λ em ≈ 400 nm)-pumped sustainable and human-centric WLED lighting. However, the development of sustainable healthy lighting is stringently restricted because few blue phosphors can be efficiently pumped by violet LED chips. Herein, we report a novel Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ blue phosphor with high quantum efficiency (>90%) and color purity (95.4%), which can efficiently convert violet light to blue emission. A crystal-site engineering approach and density functional theory (DFT) prove that the narrow-band (FWHM = 41 nm) emission of the Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ phosphor originates from the accommodation of Eu 2+ dopants in the Na(2) site. More importantly, the Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ phosphor shows zero-thermal-quenching luminescence due to a large band gap (>6 eV). By depositing the commercial Sr 2 Si 5 N 8 :Eu 2+ red phosphor, β-SiAlON:Eu 2+ green phosphor, and as-synthesized Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ blue phosphor on a 400 nm violet LED chip, the prototypical WLED can emit fullspectrum warm white light (R a = 94.3) with significantly diminished blue-light intensity. The outstanding Na 3 KMg 7 (PO 4 ) 6 :Eu 2+ blue phosphor reported here can speed up the industrialization of human-centric WLED lighting.

Eu2+-Doped Ca4Y3Si7O15N5 Phosphor with High Thermal Stability and Pressure Sensitivity for Dual-Functional Applications in W-LEDs and Pressure Sensors

“…As shown in Figure c, at 373 and 423 K, the integrated and peak emission intensities of Ca 3.99 Y 3 Si 7 O 15 N 5 :0.01Eu 2+ were about 96.17, 95.86, and 92.73, 90.66% of those at room temperature. Because of the overlap of the PLE and PL spectra, the PL spectrum will undergo thermal broadening with reabsorption . The full width at half maxima (FWHM) increases from 100.83 to 106.77 nm.…”

“…A rigid crystal lattice corresponds to a small offset. Δ R determines the value of Δ E , a smaller Δ R leads to a larger Δ E and results in a weaker thermal quenching effect. , The rigidity of the lattice can be measured by the degree of electron–phonon interaction. , The degree of electron–phonon interaction can be estimated by ascertaining a material’s Huang–Rhys factor ( S ) as follows FWHM = 8 0.25em ln nobreak0em.25em⁡ 2 0.25em ℏ ω S coth ℏ ω 2 k normalB T where ℏω is the phonon energy, k B is the Boltzmann constant, and T is the kelvin temperature. Strong electron–phonon coupling occurs when S > 5, whereas weak electron–phonon coupling tends to have S < 1 .…”

“…Because of the overlap of the PLE and PL spectra, the PL spectrum will undergo thermal broadening with reabsorption. 55 The full width at half maxima (FWHM) increases from 100.83 to 106.77 nm. The result shows that Ca 3.99 Y 3 Si 7 O 15 N 5 :0.01Eu 2+ still maintains good color stability 56 The offset (ΔR) between the two parabolas of the ground and the lowest excited levels is related to the rigidity of the crystal lattice.…”

Anionic Regulation toward Bi3+ Selective Occupation for Full-Spectrum White Light Emission

“…1−5 Among them, phosphor-converted white light-emitting diodes (pc-WLEDs) prepared from nearultraviolet (NUV) LED chips and tricolor phosphors have received much attention. 6,7 However, the coating technology used in fabricating WLED devices is quite complex, and the correlated color temperature (CCT) and color rendering index (CRI) of the emitted white light are difficult to control, which further limits their high-quality practical applications. Nowadays, the potential application of single-phase white phosphors in lighting and displays, which can effectively avoid the above problems, has attracted increased attention from researchers.…”

Highly-efficient Eu2+-activated Sr8Si4O12Cl8 cyan-emitting phosphors with zero-thermal quenching luminescence for versatile applications

“…6,7 Currently, to generate white light, there are two simple routes, that is, (i) the combination of an InGaN blue chip with Y 3 Al 5 O 12 :Ce 3+ yellow-emitting phosphors, and (ii) utilization of a near-ultraviolet (NUV) chip to pump the hybrid blue-green-red emitting phosphors. 8,9 Although white light can be generated via the first strategy, it exhibits several problems, namely, (i) the generated white light has a high correlated color temperature (CCT) and a low color rendering index (CRI), (ii) a cyan gap is existed in its luminescence spectrum, and (iii) the intense blue emission originating from the InGaN blue chip is harmful to the human eye, 10,11 thus hindering its feasibility for use in real applications. Moreover, in spite of the warm white light realized via the second route, it also suffers from a relatively low luminous efficiency and a cyan gap in its luminescence spectrum.…”