Facile Synthesis of (Sr,Ca)₂Si₅N₈:Eu²⁺-Based Red-Emitting Phosphor for Solid-State Lighting

A new facile synthetic route to produce a nitride-based red-emitting phosphor has been established. The (Sr,Ca)₂Si₅N₈:Eu²⁺-based multicomponent phosphor was successfully synthesized from the stable SrCO₃–CaCO₃–Eu₂O₃–Si₃N₄ system by simple one-step heating at 1600 °C for 4 h in an unpressurized N₂ atmosphere. The synthesized (Sr,Ca)₂Si₅N₈:Eu²⁺-based red broadband emitting phosphor exhibited the peak wavelength as long as 661 nm with a practically high external quantum efficiency of 60% under the excitation at 450 nm, while the coexisting secondary phase was inactive under the blue-light excitation, showing no detrimental effects on the photoluminescent properties. The enhanced red emission compared to the unmodified Sr₂Si₅N₈:Eu²⁺ phosphor enables further improvement of the color rendering properties of the white light-emitting diodes for solid-state lighting applications

Discovery of New Nitridosilicate Phosphors for Solid State Lighting by the Single-Particle-Diagnosis Approach

Discovery of novel luminescent materials is of fundamental importance in the advancement of solid state lighting and flat panel display technologies. In this work, we report a single-particle-diagnosis method for the discovery of new phosphors by just characterizing a luminescent crystalline particle as small as 10 μm in diameter. We explored single-particle fluorescence imaging and spectroscopy techniques to evaluate the photoluminescence of a phosphor particle distinguished from a complex powder mixture and applied a high-resolution single-crystal X-ray diffractometer to determine its crystal structure. The approach enabled us to discover two new phosphors in the Ba₃N₂–Si₃N₄–AlN ternary system: Ba₅Si₁₁Al₇N₂₅:Eu²⁺ and BaSi₄Al₃N₉:Eu²⁺. Ba₅Si₁₁Al₇N₂₅:Eu²⁺ crystallizes in the space group of <i>Pnnm</i> (no. 58) with <i>a</i> = 9.5923(2), <i>b</i> = 21.3991(5), <i>c</i> = 5.8889 (2) Å and <i>Z</i> = 2, while BaSi₄Al₃N₉:Eu²⁺ in the space group of <i>P</i>21/<i>C</i> (no.14) with <i>a</i> = 5.8465(4), <i>b</i> = 26.7255(18), <i>c</i> = 5.8386(4) Å, β = 118.897° and <i>Z</i> = 4. The single-particle photoluminescence of Ba₅Si₁₁Al₇N₂₅:Eu²⁺ shows yellow emission (λ_em = 568 nm, fwhm = 98 nm) and a quantum efficiency of 36% under the 405 nm excitation. BaSi₄Al₃N₉:Eu²⁺ shows blue emission (λ_em = 500 nm, fwhm = 67 nm) upon the 365 nm excitation

Narrow-Band Green-Emitting Phosphor Ba₂LiSi₇AlN₁₂:Eu²⁺ with High Thermal Stability Discovered by a Single Particle Diagnosis Approach

The narrow-band green-emitting phosphor Ba₂LiSi₇AlN₁₂:Eu²⁺ was discovered by analyzing a single particle in a powder mixture, which we call the single particle diagnosis approach. Single crystal X-ray diffraction analysis of the particle revealed that Ba₂LiSi₇AlN₁₂:Eu²⁺ crystallizes in the <i>Pnnm</i> space group (No. 58) with <i>a</i> = 14.0941 Å, <i>b</i> = 4.8924 Å, <i>c</i> = 8.0645 Å, and <i>Z</i> = 2. The crystal structure is composed of a corner-sharing (Si,Al)­N₄ corrugated layer and edge-sharing (Si,Al)­N₄ and LiN₄ tetrahedra. Ba­(Eu) occupies the one-dimensional channel in a zigzag manner. The luminescence properties were also measured using a single crystalline particle. Ba₂LiSi₇AlN₁₂:Eu²⁺ shows a green luminescence peak at approximately 515 nm with a narrow full-width at half-maximum of 61 nm. It shows high quantum efficiency of 79% with 405 nm excitation and a small decrease of luminescence intensity even at 300 °C

Narrow-Band Emitting Phosphor Na₂Cs₂Sr(B₉O₁₅)₂:Eu²⁺ Discovered from Local Structure Similarity with Sulfate Phosphor

Narrow-band emitting phosphors are required to improve the performance of phosphor-converted light-emitting diodes. Here, we found a new narrow-band emitting phosphor Na2Cs2Sr(B9O15)2:Eu2+ using the local structure similarity with a known narrow-band emitting phosphor. In a 2D scatter plot of the structural similarity between the local structures, the Sr site in Na2Cs2Sr(B9O15)2 was located near the Ba site of the known narrow-band emitting sulfate phosphor BaSO4:Eu2+ with a distorted local structure. We synthesized Na2Cs2Sr(B9O15)2:Eu2+ and characterized the luminescence properties by microspectroscopy. Na2Cs2Sr(B9O15)2:Eu2+ showed a violet luminescence peaked at 417 nm, and the full-width at half-maximum was as narrow as 26 nm (1497 cm–1)

Achieving Multicolor Long-Lived Luminescence in Dye-Encapsulated Metal–Organic Frameworks and Its Application to Anticounterfeiting Stamps

Long-lived luminescent metal–organic frameworks (MOFs) have attracted much attention due to their structural tunability and potential applications in sensing, biological imaging, security systems, and logical gates. Currently, the long-lived luminescence emission of such inorganic–organic hybrids is dominantly confined to short-wavelength regions. The long-wavelength long-lived luminescence emission, however, has been rarely reported for MOFs. In this work, a series of structurally stable long-wavelength long-lived luminescent MOFs have been successfully synthesized by encapsulating different dyes into the green phosphorescent MOFs Cd­(m-BDC)­(BIM). The multicolor long-wavelength long-lived luminescence emissions (ranging from green to red) in dye-encapsulated MOFs are achieved by the MOF-to-dye phosphorescence energy transfer. Furthermore, the promising optical properties of these novel long-lived luminescent MOFs allow them to be used as ink pads for advanced anticounterfeiting stamps. Therefore, this work not only offers a facile way to develop new types of multicolor long-lived luminescent materials but also provides a reference for the development of advanced long-lived luminescent anticounterfeiting materials

Extra-Broad Band Orange-Emitting Ce³⁺-Doped Y₃Si₅N₉O Phosphor for Solid-State Lighting: Electronic, Crystal Structures and Luminescence Properties

Luminescent materials play an important role in making solid state white light-emitting diodes (w-LEDs) more affordable home lighting applications. To realize the next generation of solid-state w-LEDs with high color-rendering index (CRI), the discovery of broad band and long emission wavelength luminescent materials is an urgent mission. Regarding this, the oxonitridosilicate Y₃Si₅N₉O with a high nitrogen concentration should be a suitable host material to achieve those promising luminescent properties. In this work, a phase-pure Ce³⁺-doped Y₃Si₅N₉O was successfully synthesized through the carbothermal reduction and nitridation method. Y₃Si₅N₉O:Ce³⁺ shows an emission maximum at 620 nm and an extremely broad emission band with a full-width at half-maximum (fwhm) of 178 nm. The electronic and crystal structure calculations indicate an indirect band gap of 2.6 eV (experimental value: 4.0 eV), and identify two Ce³⁺ sites with different local environments that determine the luminescence properties. The orange-emitting phosphor has the absorption, internal and external quantum efficiencies of 89.5, 17.2, and 15.6% under 450 nm excitation, respectively. The valence state of Ce, cathodoluminescence, decay time, and thermal quenching of the phosphor were also investigated to understand the structure–property relationships

Blue-Emitting Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ Discovered by a Single-Particle-Diagnosis Approach: Crystal Structure, Luminescence, Scale-Up Synthesis, and Its Abnormal Thermal Quenching Behavior

The single-particle-diagnosis approach allows for the fast discovery of novel luminescent materials using powdered samples. This paper reports a new blue-emitting Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ phosphor for solid state lighting and its scale-up synthesis. The structure-, composition-, and temperature-dependent luminescence were investigated and discussed by means of various analytic techniques including single-crystal XRD diffractometer, single-particle fluorescence spectroscopy, FTIR spectra, decay time, low-temperature luminescence, and computed energy level scheme. Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i> crystallizes in the monoclinic system (space group <i>C</i>2/<i>c</i>, no. 15) with <i>a</i> = 18.1828 (13) Å, <i>b</i> = 4.9721 (4) Å, <i>c</i> = 15.9557 (12) Å, β = 115.994 (10)^ο, and <i>Z</i> = 2. The Sr atoms are coordinated to 8 and 6 O/N atoms and located in the voids along [010] formed by vertex-sharing (Si,Al)-(O,N)₄ tetrahedra. Phase-pure powder samples of Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ were synthesized from the chemical composition of the single particle by controlling the <i>x</i> value. Luminescence of both a single particle and powders show a broad Eu²⁺ emission band centered at ∼465 nm and a fwhm of ∼70 nm, under the UV light irradiation. The title phosphor has a band gap of 5.39 eV determined from the UV–vis spectrum, absorption efficiency of 83%, internal quantum efficiency of 44.9%, and external quantum efficiency of 37.4% under the 355 nm excitation. An abnormal thermal quenching behavior is observed in Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ that has a high activation energy for thermal quenching (0.294 eV) but a low thermal quenching temperature (∼370 K), which is ascribed to the partial overlap between the Eu²⁺ excited energy level and the conduction band of the host

Blue-Emitting Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ Discovered by a Single-Particle-Diagnosis Approach: Crystal Structure, Luminescence, Scale-Up Synthesis, and Its Abnormal Thermal Quenching Behavior

The single-particle-diagnosis approach allows for the fast discovery of novel luminescent materials using powdered samples. This paper reports a new blue-emitting Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ phosphor for solid state lighting and its scale-up synthesis. The structure-, composition-, and temperature-dependent luminescence were investigated and discussed by means of various analytic techniques including single-crystal XRD diffractometer, single-particle fluorescence spectroscopy, FTIR spectra, decay time, low-temperature luminescence, and computed energy level scheme. Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i> crystallizes in the monoclinic system (space group <i>C</i>2/<i>c</i>, no. 15) with <i>a</i> = 18.1828 (13) Å, <i>b</i> = 4.9721 (4) Å, <i>c</i> = 15.9557 (12) Å, β = 115.994 (10)^ο, and <i>Z</i> = 2. The Sr atoms are coordinated to 8 and 6 O/N atoms and located in the voids along [010] formed by vertex-sharing (Si,Al)-(O,N)₄ tetrahedra. Phase-pure powder samples of Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ were synthesized from the chemical composition of the single particle by controlling the <i>x</i> value. Luminescence of both a single particle and powders show a broad Eu²⁺ emission band centered at ∼465 nm and a fwhm of ∼70 nm, under the UV light irradiation. The title phosphor has a band gap of 5.39 eV determined from the UV–vis spectrum, absorption efficiency of 83%, internal quantum efficiency of 44.9%, and external quantum efficiency of 37.4% under the 355 nm excitation. An abnormal thermal quenching behavior is observed in Sr₃Si_8–<i>x</i>Al_<i>x</i>O_7+<i>x</i>N_8–<i>x</i>:Eu²⁺ that has a high activation energy for thermal quenching (0.294 eV) but a low thermal quenching temperature (∼370 K), which is ascribed to the partial overlap between the Eu²⁺ excited energy level and the conduction band of the host

Structure, Luminescence, and Application of a Robust Carbidonitride Blue Phosphor (Al_1–<i>x</i>Si_<i>x</i>C_<i>x</i>N_1–<i>x</i>:Eu²⁺) for Near UV-LED Driven Solid State Lighting

As an extension of nitride luminescent materials, carbidonitride phosphors are also attracting great attention due to their superior thermal stability. This paper reports a blue-emitting carbidonitride phosphor Al_1–<i>x</i>Si_<i>x</i>C_<i>x</i>N_1–<i>x</i>:Eu²⁺ suitable for near ultraviolet (UV) light emitting diodes (LEDs), which is formulated by introducing SiC into AlN:Eu²⁺. With the introduction of carbon (silicon), the lattice abnormally shrinks along both <i>a</i>- and <i>c</i>-axes at low <i>x</i> values (<i>x</i> ≤ 0.08), due to the formation of a dense interlayer for accommodating the luminescence center Eu²⁺. Both of the Raman spectra and solid state NMR spectroscopy show that both Si and C are dissolved in the AlN lattice. A single blue emission band (λ_em = 472–477 nm) is observed for compositions of <i>x</i> > 0.05 by cathodoluminescence measurements. Under the 365 nm excitation, the maximum luminescence is attained for the composition of <i>x</i> = 0.06 that has an external quantum efficiency of 61% and absorption efficiency of 74.4%, which is about 11–15% higher than the corresponding carbon-free nitride sample. The thermal quenching of Al_1–<i>x</i>Si_<i>x</i>C_<i>x</i>N_1–<i>x</i>:Eu²⁺ reduces with increasing C (SiC) content, and the sample of <i>x</i> = 0.06 shows a small loss of ∼4.0% in quantum efficiency even at 200 °C. Using this phosphor in a near UV-driven white LED, a superhigh color rendering index of Ra = 95.3 and R9 = 72 as well as a color temperature of 3533 K are achieved