Potential Application In White LEDs Research Articles

Concentration- and temperature- dependent luminescence quenching and optical transition of Sr2GdTaO6: Eu3+ phosphor for potential applications in white LEDs

A series of Eu3+ doped Sr2GdTaO6 (SGT) phosphors with double perovskite structure were synthesized via a high-temperature solid-state reaction approach. The crystal structure, morphology and luminescence properties were characterized by means of X-ray diffraction, transmission electron microscope, luminescence spectroscopy and fluorescence decay lifetimes, respectively. Under the excitation of 394 nm, intense red emission in the visible region was observed in Eu3+ doped SGT phosphors, and the critical quenching concentration of Eu3+ in SGT phosphors was derived to be 15 mol%. The chromaticity coordinates and color purity of SGT: 15 mol% Eu3+ were calculated to be (0.61, 0.36) an 93.82 %, respectively. Meanwhile, it was also confirmed that the electric quadrupole–quadrupole interaction is responsible for the luminescence concentration quenching of Eu3+. The internal quantum efficiency of SGT: Eu3+ phosphors with different Eu3+ concentrations were calculated. Furthermore, the crossover process was confirmed to be the main mechanism for luminescence thermal quenching based on the temperature-dependent emission spectra and temperature-dependent fluorescence lifetimes. In addition, the Judd-Ofelt parameters, radiative transition rates and branch ratios from the 5D0 emitting states to various lower energy states were evaluated with the aid of the Judd-Ofelt theory, respectively. All results indicate that SGT: Eu3+ samples are a promising red-emitting phosphor.

Synthesis, structure, and luminescence properties of double perovskites Ba2.9Sr0.1WO6: Eu3+ red emitting phosphor

Abstract In this work, the phosphors of Eu3+ ions doped Ba2.9Sr0.1WO6 were successfully synthesized by the high-temperature solid-state method. The luminescence properties, including the emission and excitation spectra, fluorescent lifetimes, and CIE chromaticity coordinates were characterized. The crystal structure and composite of the samples were investigated by XRD (X-ray diffraction), and HRTEM (high-resolution transmission electron microscope). The emission spectra consist of the characteristic peak of Eu3+ excitation at 393 nm; the leading emission peak at 618 nm can be ascribed to the transition of 7F0 → 5L6. The optimal red emission is achieved by 2 % Eu3+ doping. This red Ba2.9Sr0.1WO6: Eu3+ has good luminescent properties and may have potential application in white LEDs.

Tunable white light photoluminescence of a single phase Tm3+/Tb3+/Eu3+ codoped GdPO4 phosphor

The present study describes the production of triply-doped GdPO4 and its optical characteristics. Structural information of the prepared material has been investigated by using X-ray diffraction and Fourier transform infrared spectroscopy. The material synthesized crystallizes into a single monoclinic crystal of space group P 21/n. The excitation curves of photoluminescence of single doped GdPO4: Tm3+, Tb3+, and Eu3+ are recorded and their emission spectra are analyzed. Triple-doped material emits multi colour light after a single UV stimulation. White light emission was seen in both triply-doped GdPO4 with variable Tm3+ concentration and triply-doped GdPO4 with variable Eu3+ concentration. GdPO4 doped with Tb3+ (7 mol%), Tm3+ (1.5 mol%), and Eu3+ (2 mol%) has colour coordinates (x = 0.3290, y = 0.3291) approximately near the value of typical white colour coordinates (x = 0.333, y = 0.3333). Furthermore, the transfer of energy in Tm3+, Tb3+ and Eu3+ in triple doped phosphor with varying Eu3+ concentrations was explained. Electric dipole-dipole interaction is used to justify and describe the process of energy transfer from Tb3+ to Eu3+. Decay time measurements were performed to explain energy transfer. Colour rendering index (CRI), Corelated colour temperature (CCT), Quantum efficiency and thermal stability of the prepared phosphor was calculated. All these parameters infer that GdPO4 doped with Tm3+, Tb3+ and Eu3+ may have potential application in white LEDs.

Effect of ZnO on the crystallization and photoluminescence of CsPbI3 perovskite quantum dots in borosilicate glasses

AbstractCsPbI3 perovskite quantum dots (QDs) doped borosilicate glass was prepared by the process of melt‐quenching and subsequent annealing. With the introduction of ZnO to the parent glass as the glass network intermediate, the optical properties of the resultant samples are dramatically enhanced. Both the photoluminescence (PL) intensity and photoluminescence quantum yield (PLQY) shows a strong dependence on ZnO concentration as ZnO is found to facilitate the precipitated of the QDs by reducing the connectivity of three‐dimensional glass network built from SiO4 tetrahedrons. The tunable visible‐band PL emission of the CsPbI3 QD‐doped glass could find potential applications in white LEDs and lasers.

Enhanced red emission in Li2Mg3TiO6: Mn4+ phosphor via Na+ and Ge4+ doping

Li 2 Mg 3 TiO 6 : Mn 4+ /Na + /Ge 4+ phosphors with rock structure have been prepared via solid state reaction method. The phosphor has broad excitation band ranging from 265 nm to 600 nm with two peaks at 345 nm and 468 nm and can give strong red emission band peaking at 667 nm. The co-doped Na + /Ge 4+ ions largely improve the luminescence properties of Li 2 Mg 3 TiO 6 : Mn 4+ . It is found that the luminescence intensity of Li 2 Mg 3 TiO 6 : Mn 4+ /Na + /Ge 4+ is increased by 132% as compared with that of Li 2 Mg 3 TiO 6 : Mn 4+ phosphor. Meanwhile the quantum efficiency of Li 2 Mg 3 TiO 6 : Mn 4+ /Na + /Ge 4+ has also increased from 32.83% to 53.55%. The mechanism of luminescence improvement may be attributed to the lowered symmetry of [TiO 6 ] octahedral sites in Li 2 Mg 3 TiO 6 host induced by the doped Na + ions and the reduction of energy transfer probability among Mn 4+ ions caused by the doped Ge 4+ ions. The developed phosphor with suitable spectral properties has potential application in white-LEDs and plant growth. • Li 2 Mg 3 TiO 6 : Mn 4+ Quantum efficiency is increased by 20.7% due to Na + /Ge 4+ co-doping. • Spectra of the phosphor conforms to lighting and plant growth application. • Lowered Mn 4+ -site symmetry and reduced Mn 4+ -Mn 4+ pairs intensify Mn 4+ luminescence. • Multi-ion substitution strategy provides valid means for improving Mn 4+ emission.

Development of bluish green-emitting Ca2-xEuxSiO4 phosphor: A novel approach using silica nanoparticles as precursor

Development of inorganic phosphors architecture is of immense concern for the growth of solid-state lighting technology. The current work focuses on the development of bluish green-emitting, silica nanoparticles assisted Ca2SiO4: Eu2+phosphors that are made via a two-step high-temperature wet-solid phase reaction technique. The optimized Eu2+ doping concentration in both the silica nanoparticles assisted Ca2SiO4: Eu2+and conventional silica assisted Ca2SiO4: Eu2+ has been calculated and found to be 5 mol%. Systematic studies viz morphology, crystal phase and photoluminescence were carried out on all the phosphor materials and their efficiencies were compared. The emission spectrum recorded at RT (Room Temperature) of the phosphor showed two prominent emission band centred at 490 and 525 nm under the excitation of 335 nm. The impregnation of silica nanoparticles in phosphors with the tailorable emissive properties has been extensively studied for their potential application in white LEDs. Finally, a prototype model of white LEDs has been fabricated using the optimized silica nanoparticle as well as conventional silica assisted Ca2SiO4: Eu2+ phosphors and their efficiencies were studied. The CIE coordinates, correlated colour temperature (CCT) and colour rendering index (CRI) were also calculated from the emission spectra of the fabricated proto-type white LED.

Spectral properties and Judd–Ofelt analysis of novel red phosphors Gd2InSbO7:Eu3+ with high color purity for white LEDs

Gd2InSbO7:Eu3+ red phosphors were successfully synthesized via high-temperature solid–state reaction. The phase purity, particle size, and luminescence properties of obtained phosphors were measured and analyzed in detail. The Gd2InSbO7 lattice possesses cubic structure with Fd-3m (227) space group. The phosphors emit bright red emission at 628 nm under 393 nm excitation, and this phenomenon is attributed to the 5D0–7F2 transition. The Judd–Ofelt parameters (Ω2, Ω4), transition ratio, and branching ratios (β) of Eu3+-doped Gd2InSbO7 phosphor were calculated on the basis of the emission spectra and decay lifetimes. The optimal content in Gd2InSbO7:xEu3+ is identified to be 15 mol%. The thermal quenching of Gd2InSbO7:Eu3+ is found to be over 500 K, and its activation energy is 0.26 eV. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of Gd2InSbO7:15%Eu3+ are (0.629, 0.371), which are close to ideal red chromaticity coordinates (0.670, 0.330). The fabricated w-LED exhibits good color rendering index (Ra) (86), correlated color temperature (CCT) (6997 K), and CIE chromaticity coordinates (0.302, 0.330). The obtained results demonstrate that Gd2InSbO7:Eu3+ phosphors have potential applications in white LEDs.

Luminescent Ag+ exchanged SOD zeolites with their potential applications in white LEDs.

Ag+ exchanged zeolites (Ag-zeolites) combining the advantages of high stability of microporous zeolites with the unique optical properties of silver clusters are attractive as promising functional materials. In this work, we systematically studied the optical properties of Ag+ exchanged SOD zeolites, obtaining tuned emission from yellow to blue and for the first time acquired white-emitting Ag-zeolite phosphors at a mild temperature (<300 °C). This tunable emission color was found to be caused by lattice shrinkage and lattice expansion of the framework in SOD zeolites. The obtained white emitting phosphors show Commission Internationale de I'Eclairage (CIE) chromaticity coordinates of (0.33, 0.34) under 395 nm excitation. In addition, we fabricated warm white LEDs with these white emitting phosphors, which show CIE coordinates of (0.37, 0.34), with a lower correlated color temperature (CCT) of 4329 K and a higher color rendering index (CRI) of 91.

Photoluminescence properties of dysprosium doped novel apatite-type Ba2Y3(SiO4)3F white-emitting phosphor

A series of novel single-phased apatite-type white-light-emitting Ba2Y3(SiO4)3F: xDy3+ (x = 0.005, 0.007, 0.01, 0.02, 0.03, 0.05, and 0.08) phosphors were prepared via a facile solid-state reaction. X-ray diffraction patterns of these phosphors revealed that all the samples have a single-phase fluorosilicate apatite with hexagonal structure. The Ba2Y3(SiO4)3F:Dy3+ phosphor can absorb in the UV–vis spectral region of 300–480 nm and presented a white light emission, including three peaks at 478, 573, and 663 nm, attributed to the 4F9/2 → 6H15/24F9/2 → 6H13/2, and 4F9/2 → 6H11/2 transitions of Dy3+ ions, respectively. The optimized doping concentration of Ba2Y3(SiO4)3F: xDy3+ ions was 2%. The Ba2Y3(SiO4)3F: 0.02Dy3+ with excellent thermal stability could maintain the emission intensity about 87% at 150 °C of that at room temperature. The chromatic properties of Ba2Y3(SiO4)3F: xDy3+ were been found into the white light region. The experimental results reveal that the synthesized phosphor has potential applications in white LEDs.

Enhancement of red emission and site analysis in Eu2+ doped new-type structure Ba3CaK(PO4)3 for plant growth white LEDs

A novel compound Ba3CaK(PO4)3 (BCKP) with new-type structure was synthesized and its structure was determined by X-ray diffraction Rietveld refinement, in which crystal structure consists of Ba1O9, Ba2O12, Ba3O9, CaO8 and KO10 polyhedra, that’s five cationic sites. As a phosphor host, Eu2+ doped BCKP emits cold white light with about 90% quantum efficiency (QE) through entering different cationic sites. Based on the results of refinement, three Eu2+ luminescence centers in sites Ca, Ba2 and K were clearly assigned in Eu2+ solely doped BCKP by the time-resolved emission spectra (TRES), Van Uitert equation, but the emissions of Eu2+ at Ba1 and Ba3 sites are not easy to be determined for the same coordination number (CN). According to their different spatial distribution of the coordinated atoms, the first-principles calculation was used to compute the d orbital splitting energy of Eu2+ ions in Ba1 and Ba3 sites to accurately distinguish the ambiguous luminescence centers. In order to meet the requirement of plant growth spectra, Mn2+ was introduced into BCKP: Eu2+ to enhance the red component of spectra, which not only perfectly match with the absorption spectra of carotenoid and chlorophyll-b, but also LEDs fabricated through combining 365 nm near ultraviolet (n-UV) chip with BCKP: Eu2+, Mn2+ phosphor exhibit excellent parameters including high color rendering index (Ra) (92), excellent correlated color temperature (CCT) (4486 K) and outstanding QE up to 65%. Results confirmed that BCKP: Eu2+/Mn2+ phosphor with great potential applications in white LEDs and plant growth.

Luminescence and energy transfer properties of color-tunable Sr4La(PO4)3O: Ce3+, Tb3+, Mn2+ phosphors for WLEDs

A series of Sr4La(PO4)3O: Ce3+, Tb3+, Mn2+ phosphors have been synthesized with a high temperature solid-state method. The luminescence properties, thermal stability, and energy transfer from Ce3+ to Tb3+ and Mn2+ in Sr4La(PO4)3O were investigated in detail. Through energy transfer, the weak green emission from Tb3+ and red emission from Mn2+ can be significantly enhanced by the introduction of the sensitizer Ce3+ ions. The emission color can be tuned by changing the ratio of Ce3+/Tb3+ and Ce3+/Mn2+ ions. White light was obtained with chromaticity coordinates of (0.3326, 0.3298) in the Sr4La(PO4)3O: 0.12Ce3+, 0.3Mn2+ sample, indicating that the Sr4La(PO4)3O: Ce3+, Tb3+, Mn2+ phosphors may have potential application in white LEDs.

Preparation and luminescent properties of new YAG:Ce3+ phosphor in glass (PIG) for white LED applications

A yellow-emitting phosphor-in-glass (PIG) material was synthesized by dispersing commercial YAG:Ce3+ phosphor powder in homemade host glass prepared by melting-quenching method. The phase composition, microstructure and photoluminescence properties of PIG were investigated by means of XRD, SEM, fluorescence spectrophotometer and optoelectronic testing system. The results showed that the YAG:Ce3+ phosphor particles were uniformly distributed and well preserved in glass matrix without any decomposition reaction. The bulk PIG can be efficiently exited by 460 nm to emit a broad yellow emission peak (530 nm) attributed to 5d → 4f transition of Ce3+ ion. The optimal luminous property of PIG can be achieved when YAG:Ce3+ phosphor concentration, melting temperature and thickness are 8 wt%, 950 °C and 1.5 mm, respectively. Under driving current of 540 mA, the luminous efficiency of the white LED device packaged by the as-prepared PIG and blue LED chip is 98 lm/W, and its color coordinate, color temperature and color rendering index are (0.300, 0.339), 7125 K and 71, respectively. This finding shows potential applications in white LEDs for the as-prepared PIG material.

Tunable broad photoluminescence in Cu+/Mn2+ co-doped oxyfluoride glasses sintered in air atmosphere

In order to explore luminescent materials for spectra modification, a series of Cu+ and Mn2+ doped oxyfluoride glasses were successfully prepared via melt-quenching method. A simple, efficient and universal method was used to gain monovalent copper ions in air atmosphere by adding aluminum powder as reducing agent. The luminescent properties of glasses were systematically investigated through optical absorption, photoluminescence and decay curves. Under ultraviolet excitation, Cu+ singly doped glass emits broad luminescence band, and its emission band shifts to red with increasing excitation wavelength. Through an efficient energy transfer process, Cu+-Mn2+ co-doped samples generate the varied hues from blue to white and eventually to red. Luminescent quantum yield and energy transfer efficiency were obtained. Our results demonstrate that Cu+-Mn2+ co-doped glasses have potential application in white LEDs as well as photosynthesis of green plants.

Eu2+-doped Sr5(PO4)3Br blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Eu2+-doped bromophosphateapatite Sr5(PO4)3Br phosphors were synthesized by the conventional high-temperature solid-state reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal stability and CIE chromaticity coordinates were systematically investigated. Photoluminescence spectra of Sr5(PO4)3Br:Eu2+ exhibit a single blue emission at 450 nm under the excitation of 345 nm, which is ascribed to the 4f–5d transition of Eu2+. The phosphor shows very good thermal stability. The CIE color coordinates are very close to those of BaMgAl10O17:Eu2+ (BAM). All the properties indicate that the blue-emitting Sr5(PO4)3Br:Eu2+ phosphor has potential application in white LEDs.

Investigation on luminescence of emission-tunable Ca5Y3Na2(PO4)5SiO4F2:Eu2+,Tb3+,Mn2+ phosphors for white LEDs

To explore new single-phased white-light-emitting luminescent materials, a series of Eu2+-Tb3+-Mn2+ doped Ca5Y3Na2(PO4)5SiO4F2 (CYNPS) phosphors were synthesized by solid-state reaction method. Eu2+ in the CYNPS host shows a light blue emission band covering a broad range from 400 to 800 nm. When the Tb3+ or Mn2+ is codoped with Eu2+, obvious energy transfer from Eu2+ to Tb3+/Mn2+ appears, which increases the emission intensity of Tb3+/Mn2+ efficiently. To achieve white emission, the Eu2+-Tb3+-Mn2+ ions are tridoped. By adjusting the Mn2+ concentration, the emitting-light-color can be tuned conveniently. Warm white light was gained in the CYNPS:0.07Eu2+,0.18Tb3+,0.15Mn2+ phosphor with the chromaticity coordinates and correlated color temperature of (0.396, 0.369) and 3487 K, respectively. The investigation reveals that the present phosphors could have potential application in white LEDs.

Reduction of Eu3+ to Eu2+ in α-Y2Si2O7 and X1-Y2SiO5 and their luminescent properties

Due to its bright tunable emission, Eu-doped yttrium silicates are very interesting materials for LED applications. The microparticles of α-Y1.98 Eu0.02 Si2O7 and the low-temperature phase of Y1.98 Eu0.02 SiO5 (X1) were prepared by sol gel technique. Then, the samples were reduced at high temperatures using pure hydrogen as reduction agent. The materials obtained were characterized by X-Ray diffraction, Scanning Electron Microscopy, Energy Dispersive X-Ray and Photoluminescence spectroscopy. The presence of Eu2+ in the materials after the reduction was confirmed by the blue-green band emission and the wide absorption band, observed only in the excitation spectra of the reduced samples. These bands are congruent with the information previously reported in the literature. A red shift of the broadband emission of Eu2+ doped α-Y2Si2O7 system was observed compared to previously reported results. Also, the luminescent properties of Eu2+ host in X1-Y2SiO5 are presented for first time. The relative contribution of Eu2+ and Eu3+ depends on the excitation wavelength leading to a tunable emission phosphor with potential application in white LEDs. Summarizing, the reduction of Eu ions in yttrium silicates is presented in this work, leading to a tunable emission phosphor with potential application in white LEDs.

Preparation, structure, luminescence properties of europium doped zinc spinel structure green-emitting phosphor ZnAl2O4:Eu2+

The Zn1–xAl2O4:xEu2+ phosphor powders were synthesized by the solid-state reaction method. The synthesis temperature for ZnAl2O4 was optimized, whereas the phase structure, TEM images, photoluminescence (PL) properties, the concentration quenching mechanism, the fluorescence decay curves, as well as the CIE chromaticity coordinates of the samples were investigated in details. Under the excitation at 379 nm, the phosphor exhibits an asymmetric broad-band green emission with a peak at 532 nm, which is ascribed to the 5d–4f transition of Eu2+. When the doping concentration of Eu2+ ions is 0.01, the luminescence intensity of the sample reaches the maximum value. It is further proved that the exchange interaction results in the concentration quenching of Eu2+ in the Zn1–xAl2O4:xEu2+ phosphor powders. The thermal quenching property of ZnAl2O4:Eu2+ phosphor was investigated and the quantum efficiency (QE) values of the selected Zn0.99Al2O4:0.01Eu2+ phosphor was measured and determined as 54.85%. The lifetime of the optimized sample Zn0.99Al2O4:0.01Eu2+ is 3.0852 μs and the CIE coordinate of the sample was calculated as (0.3323, 0.5538) with high-color-purity green emission. All properties indicate that the green-emitting ZnAl2O4:Eu2+ phosphor powder has potential application in white LEDs.

Luminescence and energy transfer in warm white-light-emitting K3Y(PO4)2:Tb,Eu phosphor for LEDs applications

To obtain warm white-emission in a new single-phase phosphor, a series of Tb–Eu doped K3Y(PO4)2 (KYP) samples were prepared by solid-state reaction method, and their photoluminescence properties were investigated. For Tb-single-doped KYP, the green emission mainly owing to the 5D4–7FJ (J = 3–6) transitions was obtained. For Eu-single-doped KYP, two kinds of emissions were observed, i.e., the line-peak and broad-band emissions, belonging to the Eu3+ 5D0–7FJ (J = 0–4) and Eu2+ d–f transitions, respectively. When Tb–Eu ions were co-doped into the KYP host, the Eu2+, Tb3+ and Eu3+ emissions were all found, which contribute to the blue, green and red components in the visible spectrum, respectively. By adjusting the relative concentrations of Tb and Eu, the emitting light color can be tuned and the warm white-emission was gained in the KYP:0.03 Tb,0.03Eu phosphor. The thermal luminescence stability of the KYP:0.03 Tb,0.03Eu sample was studied. The above investigations reveal that the present phosphors could have potential application in white LEDs.

Luminescence properties of Pr3+ doped (Y0.9La0.1)2O3 transparent ceramics for potential applications in white LEDs and scintillators

(PrxY0.9La0.1)2O3 (x = 0.05, 1, 5) transparent ceramics were fabricated by conventional ceramic processing. The absorption, emission spectra excited by ultraviolet and X-ray as well as the excitation spectra have been investigated as a function of the Pr3+ concentration. The emission under ultraviolet excitation shows the ability of Pr3+ to downconvert ultraviolet light to blue emission. The strong excitation band at 430–520nm is in good agreement with the emissions of InGaN blue chips (λem = 450–470nm), which can be efficiently excited by the 470nm light and generate bright red emission at around 630nm. The radioluminescence spectra demonstrate the possible application of Pr3+: (Y0.9La0.1)2O3 in scintillator. In addition, the concentration quenching observed in the case of the P1 and P5 ceramics leads us to conclude that an optimum Pr3+ concentration to generate the best luminescence properties is achievable. Given overall luminescence properties, the low Pr3+ content (0.5mol%) doped (Y0.9La0.1)2O3 transparent ceramic is a potential candidate for the applications in the ultraviolet-based and InGaN blue chip based white light-emitting diodes, as well as the scintillators.

Tunable emitting phosphors K3Gd(PO4)2: Tm3+-Dy3+ for light-emitting diodes and field emission displays

Spectroscopic properties of K3Gd(PO4)2: Tm3+-Dy3+ under ultraviolet (UV) light and low-voltage electron beam excitations were investigated. Upon direct excitation Tm3+ from its 6F6 level to 1D2 level, the decrease of emission intensity and lifetime of Tm3+ 1D2-3F4 emission with increasing concentration of Dy3+ in K3Gd(PO4)2: Dy3+, Tm3+ confirmed the occurrence of energy transfer from Tm3+ to Dy3+. Besides, K3Gd(PO4)2: Dy3+, Tm3+ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm3+. When 1% Tm3+ and 8% Dy3+ were codoped in the K3Gd(PO4)2, intensive white emitting light with CIE of (0.338, 0.347) was achieved upon 358 nm excitation. The cathodoluminescence spectra of K3Gd(PO4): Tm3+, Dy3+ phosphors as a function of accelerating voltage and filament current were also measured. Under low-voltage electron-beam excitation, K3Gd(PO4)2: Tm3+, Dy3+ phosphors exhibit excellent tunable emitting property. All of the above results reveal that the as-prepared K3Gd(PO4)2: Tm3+, Dy3+ phosphors have potential applications in white LEDs and FEDs.