Synthesis and luminescent properties of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript> blue–green emitting phosphor for white light-emitting diodes (LEDs)

An efficient blue–green emitting phosphor, Sr₄Al₁₄O₂₅:Eu²⁺, was prepared by solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Sr₄Al₁₄O₂₅:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 8–10 μm. Photoluminescence measurements showed a broad absorption band between 300 and 450 nm which was efficiently excited by near-ultraviolet (NUV) LEDs (350–410 nm) and a strong emission band peaking at 491 nm. A bright blue–green LED with chromatic coordination (0.176, 0.412) was fabricated by incorporating the phosphor with an InGaN-based NUV chip, which indicates that Sr₄Al₁₄O₂₅:Eu²⁺ is a good candidate phosphor for application in white LEDs.     

Synthesis and luminescent properties of SrAl2O4:Eu green-emitting phosphor for white LEDs

SrAl₂O₄:Eu²⁺ phosphor was prepared by a solid-state reaction in CO-reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of SrAl₂O₄:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 7–8 μm. Photoluminescence measurements showed that the phosphor can be efficiently excited by UV–visible light from 350 to 430 nm, and exhibited bright green emission peaked at about 516 nm. Bright green LEDs were fabricated by incorporating the phosphor with an InGaN-based UV chip. All the characteristics indicated that SrAl₂O₄:Eu²⁺ is a good candidate phosphor applied in white LEDs.     

Synthesis,structure and photoluminescence properties of (Sr,Ca)AlSiN<Subscript>3</Subscript>:Eu<Superscript>2+</Superscript> phosphor for white light emitting diodes with controllable optical performance

A series of Sr_yCa_1?x?yAlSiN₃:xEu²⁺ (x = 0–0.01, y = 0–0.8) phosphors have been successfully prepared by solid state reaction under atmospheric pressure. All the phosphors exhibit orthorhombic crystal structure similar with CaAlSiN₃ structure. It is found that the emission bands for all Ca_1?xAlSiN₃:xEu²⁺ phosphors are centered at ~650 nm and fluorescence quenching has been observed along with the increase of Eu²⁺ concentration in host materials. Through substitution of Ca²⁺ by Sr²⁺, an expected red emission peak (625 nm) and enhanced luminescent intensity can be achieved. The obtained Sr_0.8Ca_0.192AlSiN₃:0.008Eu²⁺ phosphor was further used as efficient red component to fabricate white light emitting diodes (LEDs). Under the optimized condition of LED packaging, the white LEDs own the excellent optical properties with luminous efficiency of 90.6 lm/W and an ideal color rendering index (Ra = 82). Furthermore, the color correlated temperature of white LEDs can be simply adjusted through changing the red phosphor concentration and dispensing package saves time.     

Synthesis,crystal structure and luminescence in Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript>

Bluish green emitting phosphor, Ca₃Al₂O₆:Ce³⁺, is prepared by low-temperature combustion method. X-ray diffraction, photoluminescence, scanning electron microscopy techniques are used to characterize the synthesized phosphor. The most efficient bluish green (483 nm) emission is observed under the excitation by near UV light. The emission characteristics are credited to 5d → 4f type transitions in Ce³⁺. The luminescence properties of Eu²⁺ are predicted for the first time from those of Ce³⁺. Also, photoluminescence of Eu³⁺ is studied in the same host. The emission spectrum of Ca₃Al₂O₆:Eu³⁺ shows the peak at 592 (orange) and 614 nm (red) wavelengths. Ca₃Al₂O₆:Ce³⁺phosphor can be a potential blue phosphor for field emission display, solid-state lighting and LED.     

Eu3+, Sm3+ Deep‐Red Phosphors as Novel Materials for White Light‐Emitting Diodes and Simultaneous Performance Enhancement of Organic–Inorganic Perovskite Solar Cells

The luminous efficiency of inorganic white light‐emitting diodes, to be used by the next generation as light initiators, is continuously progressing and is an emerging interest for researchers. However, low color‐rendering index (Ra), high correlated color temperature (CCT), and poor stability limit its wider application. Herein, it is reported that Sm³⁺‐ and Eu³⁺‐doped calcium scandate (CaSc₂O₄ (CSO)) are an emerging deep‐red‐emitting material with promising light absorption, enhanced emission properties, and excellent thermal stability that make it a promising candidate with potential applications in emission display, solid‐state white lighting, and the device performance of perovskite solar cells (PSCs). The average crystal structures of Sm³⁺‐doped CSO are studied by synchrotron X‐ray data that correspond to an extremely rigid host structure. Samarium ion is incorporated as a sensitizer that enhances the emission intensity up to 30%, with a high color purity of 88.9% with a 6% increment. The impacts of hosting the sensitizer are studied by quantifying the lifetime curves. The CaSc₂O₄:0.15Eu³⁺,0.03Sm³⁺ phosphor offers significant resistance to thermal quenching. The incorporation of lanthanide ion‐doped phosphors CSOE into PSCs is investigated along with their potential applications. The CSOE‐coated PSCs devices exhibit a high current density and a high power conversion efficiency (15.96%) when compared to the uncoated control devices.     

Tunable color emitting of CaAl2Si2O8: Eu,Tb phosphors for light emitting diodes based on energy transfer

A series of single-phased CaAl₂Si₂O₈: Eu, Tb phosphors have been synthesized at 1400 °C via a solid state reaction. The emission bands of Eu²⁺ and Eu³⁺ were observed in the air-sintered CaAl₂Si₂O₈: Eu phosphor due to the self-reduction effect. Tb³⁺ ions that typically generated green emission were added in CaAl₂Si₂O₈: Eu phosphor for contributing for a wider-range tunable emission. Energy transfer from Eu²⁺ to Tb³⁺ and the modulation of valence distribution of Eu²⁺/Eu³⁺ that contributes to the tunable color emitting were elucidated. More importantly, a white emission can be obtained by controlling the codoped contents of Li⁺ as well as suppressing the self-reduction degree of Eu. The white light emitting with the color coordinate (0.326, 0.261) was obtained, which indicates that CaAl₂Si₂O₈: Eu, Tb is a promising tunable color phosphor for application in ultraviolet light emitting diodes (UV-LEDs).     

A novel blue-emitting NaSrPO4:Eu phosphor for near UV based white light-emitting-diodes

A novel blue-emitting phosphor based on a phosphate host matrix, NaSrPO₄:Eu²⁺, was prepared by a conventional solid-state reaction method. The NaSrPO₄:Eu²⁺ phosphor was efficiently excited at wavelengths of 250-450 nm, which is suitable for the emission band of near ultraviolet (n-UV) light-emitting-diode (LED) chips (350-430 nm). The NaSrPO₄:Eu²⁺ phosphor exhibits a strong blue emission peaking at 453 nm and broadly weak green and red emission bands up to 700 nm. The effect of the activated Eu²⁺ concentration on the emission intensity of the NaSrPO₄:Eu²⁺ was also investigated. Here, a phosphor-converted LED (pc-LED) was fabricated and exhibits bright blue emission under a forward bias of 20 mA. All of these characteristics suggest that the NaSrPO₄:Eu²⁺ phosphors could be applicable to n-UV based white LEDs.     

Photoluminescence spectra tuning of Eu2+ activated orthosilicate phosphors used for white light emitting diodes

Divalent europium activated alkaline earth orthosilicate M₂SiO₄ (M = Ba, Sr, Ca) phosphors were synthesized through solid-state reaction technique and their luminescent properties were investigated. Photoluminescence emission spectra of Sr₂SiO₄:Eu²⁺ phosphor was tuned by substitution of Sr²⁺ with 10 mol% Ca²⁺ or Mg²⁺. Two emission bands originated from the 4f–5d transition of Eu²⁺ ion doped into different cation sites in the M₂SiO₄ host lattice were observed under ultraviolet excitation. The Sr₂SiO₄:Eu²⁺ phosphor showed a blue and a green broad emission bands peaked around 475 and 555 nm with some variation for different Eu²⁺ doping concentration. When 10 mol% of Sr²⁺ was substituted by Ca²⁺ or Mg²⁺, the blue emission band blue-shifted to 460 nm and the green emission band shifted to even longer wavelength. An energy loss due to energy transfer from one Eu²⁺ to another Eu²⁺ ion, changing of the crystal field strength and covalence in the host lattice together were assigned for the tuning effect. With an overview of the excitation spectra and the emission spectra in blue and green-yellow color, these co-doped phosphors can become a promising phosphor candidate for white light-emitting-diodes (LEDs) pumped by ultraviolet chip.     

Luminescent and thermal properties of a new green emitting Ca6Sr4(Si2O7)3Cl2:Eu2+ phosphor for near-UV light-emitting diodes

A novel green emitting phosphor, Eu²⁺-activated Ca₆Sr₄(Si₂O₇)₃Cl₂, was synthesized using the solid-state reaction and its temperature-dependent luminescence characteristic was reported for the first time. Crystallographic site-occupations of Eu²⁺ ions in this host were assigned and two distinguishable Sr²⁺ sites were confirmed. As the temperature increases, the emission lines of Ca₆Sr_3.99(Si₂O₇)₃Cl₂:0.01Eu²⁺ show an anomalous blue-shift along with the broadening bandwidth and decreasing emission intensity, which is ascribed in terms of the phonon-assisted back tunneling from the excited state of low-energy emission band to the high-energy emission band in the configuration coordinate diagram. Further, the luminescence quenching temperature, the activation energy for thermal quenching (ΔE), and the chromaticity coordinates were also investigated. In view of its preferable excitation spectrum profile, intense green emission peaking at 511 nm, and high thermal luminescence stability, the as-prepared phosphor is expected to find applications as a new green emitting phosphor for near-UV light emitting diodes.     

A novel blue emitting phosphor NaBa<Subscript>0.98</Subscript>Eu<Subscript>0.02</Subscript>PO<Subscript>4</Subscript> and the improvement of its luminescence properties

A novel blue-emitting phosphor NaBa_0.98Eu_0.02PO₄ was synthesized by conventional solid state reaction, and it exhibits efficient blue emission under near-ultraviolet (n-UV) excitation. The emission spectrum shows a single band centered at about 440 nm, which corresponds to the 4f⁶5d¹-4f⁷ transition of Eu²⁺. The excitation spectrum is a broad band in the wavelength range between 200 and 450 nm, which can match the emission of white light emitting diodes (LEDs) by the method of n-UV conversion. The Ca²⁺, Sr²⁺ and Mg²⁺ were co-doped into NaBa_0.98Eu_0.02PO₄ respectively. Special attention was paid to the sample co-doped with Ca²⁺ that could possess a higher luminous efficacy than the analogs co-doped with Sr²⁺ and Mg²⁺. With the co-doping of Ca²⁺, the enhanced intensity of the excitation and emission band appears. The optimum co-doping concentration of Ca²⁺ is 7 mol.%. The emission intensity of NaBa_0.91Ca_0.07Eu_0.02PO₄ phosphoris about 1.68 times than that of NaBa_0.98Eu_0.02PO₄ phosphor. The as-prepared phosphors are the potential blue phosphors for application in white LEDs.     

Luminescent properties of Li2CaSiO4:Eu2+ phosphor

Li₂CaSiO₄:Eu²⁺ phosphors with single phase were successfully synthesized by the solid state reaction method and their photoluminescence properties were studied. The experimental results on Li₂CaSiO₄:Eu²⁺, summarized in effective absorption and excitation in the ultra-violet region, strong emission in the blue spectrum and the CIE Chromaticity coordinate (0.10, 0.20), indicate this phosphor has great potential in ultra-violet chip pumped white LEDs. A comparative investigation of the emission intensity suggests that Li₂CaSiO₄:Eu²⁺ has the best performance with Eu²⁺ concentration of 1% and excitation of 375 nm. Compound phosphors of Li₂CaSiO₄:Eu²⁺ and Li₂SrSiO₄:Eu²⁺ show two emission bands in the blue and yellow region. With the molar ratio of Li₂CaSiO₄:Eu²⁺ to Li₂SrSiO₄:Eu²⁺ being 1:1 and excitation of 390 nm, the CIE Chromaticity coordinate was tuned to be (0.32, 0.36), which is close to that of natural white light, indicating this may become blue phosphor candidate for ultra-violet chip pumped and multi-phosphors converted white LEDs.     

Near UV and blue-based LED fabricated with Ca8Zn(SiO4)4Cl2:Eu as green-emitting phosphor

Green-emitting phosphor Ca₈Zn(SiO₄)₄Cl₂:Eu²⁺ has been prepared by the solid state reaction method and there luminescence properties are investigated. The excitation spectrum of Ca₈Zn(SiO₄)₄Cl₂:Eu²⁺ shows an intense excitation band in the blue centered at 450 nm and emits with a maximum at 505 nm. The concentration quenching mechanism is studied and verified to be the energy transfer among the nearest-neighbor ions. Upon 450 nm excitation, the emission intensity of Ca₈Zn(SiO₄)₄Cl₂:Eu²⁺ is much stronger than the green emitting Ca₃SO₄Cl₂:Eu²⁺ phosphor and even higher than YAG:Ce³⁺. This excitation spectrum range matches UV and blue light-emitting diodes (LEDS) chips very well, suggesting Ca₈Zn(SiO₄)₄Cl₂:Eu²⁺ could be a promising green emitting phosphor candidate for LED devices.     

Optimization of Low‐Dimensional Components of Quasi‐2D Perovskite Films for Deep‐Blue Light‐Emitting Diodes

Compared to efficient green and near‐infrared light‐emitting diodes (LEDs), less progress has been made on deep‐blue perovskite LEDs. They suffer from inefficient domain [various number of PbX₆^? layers (n)] control, resulting in a series of unfavorable issues such as unstable color, multipeak profile, and poor fluorescence yield. Here, a strategy involving a delicate spacer modulation for quasi‐2D perovskite films via an introduction of aromatic polyamine molecules into the perovskite precursor is reported. With low‐dimensional component engineering, the n₁ domain, which shows nonradiative recombination and retarded exciton transfer, is significantly suppressed. Also, the n₃ domain, which represents the population of emission species, is remarkably increased. The optimized quasi‐2D perovskite film presents blue emission from the n₃ domain (peak at 465 nm) with a photoluminescence quantum yield (PLQY) as high as 77%. It enables the corresponding perovskite LEDs to deliver stable deep‐blue emission (CIE (0.145, 0.05)) with an external quantum efficiency (EQE) of 2.6%. The findings in this work provide further understanding on the structural and emission properties of quasi‐2D perovskites, which pave a new route to design deep‐blue‐emissive perovskite materials.     

Luminescence properties of Eu2+-activated Sr5(PO4)2(SiO4) for green-emitting phosphor

A green-emitting phosphor of Eu²⁺-activated Sr₅(PO₄)₂(SiO₄) was synthesized by the conventional solid-state reaction. It was characterized by photoluminescence excitation and emission spectra, and lifetimes. In Sr₅(PO₄)₂(SiO₄):Eu²⁺, there are at least two distinguishable Eu²⁺ sites, which result in one broad emission situating at about 495 nm and 560 nm. The phosphor can be efficiently excited in the wavelength range of 250–440 nm where the near UV (～ 395 nm) Ga(In)N LED is well matched. The dependence of luminescence intensities on temperature was investigated. With the increasing of temperature, the luminescence of the phosphor shows good thermal stability and stable color chromaticity. The luminescence characteristics indicate that this phosphor has a potential application as a white light emitting diode phosphor.     

Luminescence and structural properties of Eu3+ doped BaY2ZnO5 for LED solid-state lighting application

Eu³⁺ doped BaY_2(1?x)ZnO₅ phosphor was successfully synthesized by a single step solution combustion process. The crystal structure and particle morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. The XRD results suggest that BaY₂ZnO₅ crystallizes in a single phased orthorhombic structure with space group Pbnm at 1,100 °C. The phosphor can be effectively excited by near-UV light, emitting intense red luminescence (628 nm) corresponding to the hypersensitive ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions, located at low-symmetry site with no inversion center in BaY₂ZnO₅ crystal lattice. Fluorescence decay analysis was carried out to understand the energy transfer mechanism and quenching behavior of luminescence of Eu³⁺ ions in the BaY₂ZnO₅ phosphor. The BaY₂ZnO₅: Eu³⁺ emission (λ_ex = 395 nm) could be tuned from blue to white and red light by varying the Eu³⁺ ions concentration, making this phosphor as a promising candidate for LEDs application.     

Synthesis of new green-emitting KBa1−xScSi3O9:Eu2+x phosphors for white LEDs

New green-emitting KBa_1−xScSi₃O₉:Eu²⁺_x phosphors for white LEDs were synthesized by a conventional solid-state reaction method. The obtained KBa_1−xScSi₃O₉:Eu²⁺_x phosphors show the strong broad optical absorption band from UV to blue light region and exhibit broad green emission with a peak at 521 nm under excitation at 405 nm due to the allowed 4f⁶5d¹−4f⁷ transition of Eu²⁺. Optimization of Eu²⁺ concentration resulted in the highest green emission peak intensity was obtained at the composition of KBa_0.94ScSi₃O₉:Eu²⁺_0.06, and the relative emission intensity of this phosphor was 32% of that of a commercial YAG:Ce³⁺ phosphor.     

Synthesis and luminescence properties of Ca8NaGd(PO4)6F2: Eu2+, Mn2+ for white LEDs

A series of luminescent emission-tunable phosphors Ca₈NaGd(PO₄)₆F₂: Eu²⁺, Mn²⁺ have been prepared by a combustion-assisted synthesis method. The X-ray diffraction measurement results indicate that the crystal structure of the phosphor is a single phase of Ca₈NaGd(PO₄)₆F₂. The photoluminescence (PL) properties of Eu²⁺ and Mn²⁺-codoped Ca₈NaGd(PO₄)₆F₂ phosphors were also investigated. The phosphors can be efficiently excited by ultraviolet (UV) light and show a blue emission band at about 450 nm and a yellow emission band at about 574 nm, which originated from the Eu²⁺ ions and the Mn²⁺ ions, respectively. The efficient energy transfer from the Eu²⁺ ions to the Mn²⁺ ions was observed and its mechanism should be a resonant type via a nonradiative dipole–quadrupole interaction. A color-tunable emission in Ca₈NaGd(PO₄)₆F₂ phosphors can be realized by Eu²⁺ → Mn²⁺ energy transfer. Our results indicate that the developed phosphor may be used as a potential white emitting phosphor for UV based white LEDs.     

A novel blue emitting phosphor NaBa0.98Eu0.02PO4 and the improvement of its luminescence properties

A novel blue-emitting phosphor NaBa_0.98Eu_0.02PO₄ was synthesized by conventional solid state reaction, and it exhibits efficient blue emission under near-ultraviolet (n-UV) excitation. The emission spectrum shows a single band centered at about 440 nm, which corresponds to the 4f⁶5d¹-4f⁷ transition of Eu²⁺. The excitation spectrum is a broad band in the wavelength range between 200 and 450 nm, which can match the emission of white light emitting diodes (LEDs) by the method of n-UV conversion. The Ca²⁺, Sr²⁺ and Mg²⁺ were co-doped into NaBa_0.98Eu_0.02PO₄ respectively. Special attention was paid to the sample co-doped with Ca²⁺ that could possess a higher luminous efficacy than the analogs co-doped with Sr²⁺ and Mg²⁺. With the co-doping of Ca²⁺, the enhanced intensity of the excitation and emission band appears. The optimum co-doping concentration of Ca²⁺ is 7 mol.%. The emission intensity of NaBa_0.91Ca_0.07Eu_0.02PO₄ phosphoris about 1.68 times than that of NaBa_0.98Eu_0.02PO₄ phosphor. The as-prepared phosphors are the potential blue phosphors for application in white LEDs.     

Synthesis and optical properties of KCaPO4:Eu phosphor

A series of Eu²⁺ doped KCaPO₄ phosphors were prepared by high temperature solid state reaction and an efficient blue-green emission was observed. The photoluminescence (PL) spectrum of the phosphor appeared one asymmetric peak under near-ultraviolet (n-UV) excitation and two emission bands at 480 nm and 540 nm were obtained using Gaussian fit, which was because Eu²⁺ ions inhabited two different Ca²⁺ sites: Eu(I) and Eu(II) in the host lattice, respectively. The excitation spectrum was a broadband extending from 250 to 450 nm, which matched well with the emission of ultraviolet light-emitting diodes (UV LEDs). The effect of Eu²⁺ concentration on the emission intensity of KCaPO₄:Eu²⁺ phosphor was investigated in detail.     

Luminescent properties of Ca2BO3Cl:Eu yellow-emitting phosphor for white light-emitting diodes

The Ca₂BO₃Cl:Eu²⁺ phosphor was synthesized by the general high temperature solid-state reaction and an efficient yellow emission under near-ultraviolet and blue excitation was observed. The emission spectrum shows a single intense broad emission band centered at 573 nm, which corresponds to the allowed f-d transition of Eu²⁺. The excitation spectrum is very broad extending from 350 to 500 nm, which is coupled well with the emission of UV LED (350-410 nm) and blue LED (450-470 nm). The measured emission of In-GaN-based Ca₂BO₃Cl:Eu²⁺ LED shows white light to the naked eye with a chromatic coordinate of (0.33, 0.36). The Ca₂BO₃Cl:Eu²⁺ is a very appropriate yellow-emitting phosphor for white LEDs.