White Light Applications Research Articles

Structure and photoluminescence properties of Dy3+ doping in Sr-Si-O-N frameworks for highly efficient white light and optical information storage applications

A series of Dy3+ doped Sr-Si-O-N frameworks with single phase were successfully developed by a two-step synthetic method. Under excitation of NUV light, Dy3+ singly-doped SrSi2O2N2 (a typical Sr-Si-O-N framework) phosphors exhibited two emission peaks at 478 nm and 571 nm, corresponding to blue (4F9-2→6H15-2) and yellow (4F9-2→6H13-2) emissions of Dy3+ ions. Compared with the traditional solid state reaction, the two-step method facilitated the formation of SrSi2O2N2: Dy3+ phosphor with pure phase and greatly enhanced the photoluminescence emission intensity (~4 times). The emission intensities of SrSi2O2N2: xDy3+ phosphors reached the maximum when x = 0.06 due to the concentration quenching, which was confirmed to be electric dipole-electric dipole interaction. The SrSi2O2N2: Dy3+ phosphors with an excellent thermal stability can be regarded as the potential single phase white-light phosphors when excited by NUV light. The optimal chromaticity coordinate of white light is (0.3347, 0.3966) for SrSi2O2N2: 0.06Dy3+ phosphor. Interestingly, the single green emission band at 525 nm was observed and a unique thermo-stimulated luminescence property was demonstrated for Dy3+/Eu2+ co-doped SrSi2O2N2 phosphors. A specific photographic pattern (for example pentagon pattern) was obtained by covered the mask on the surface of SrSi2O2N2: Eu2+, Dy3+ pellets under excitation of UV light. After UV lights turn off, the pentagon patterns were reproduced by heating the SrSi2O2N2: Eu2+, Dy3+ pellets. It was validated from the decrease of PL emission intensity and decay time with the increasing Dy3+ content that Dy3+ ions were acted as the deep trap centers. Similar thermal-stimulated luminescence was also found for Eu2+ singly-doped SrSi2O2N2 phosphor due to the oxygen vacancy in host lattice. Furthermore, the mechanism of thermal-stimulated luminescence has been proposed and Dy3+/Eu2+ co-doped SrSi2O2N2 phosphors with deep traps are suitable to be the good candidates for optical information storage applications.

Investigation of luminescence properties of Dy3+ doped LiF–Na2O– K2O–B2O3 glasses for white light generation

In this work Dy2O3 doped tri-alkali oxyfluoro-borate (NKLB-Dy) glasses were prepared by melt quenching technique for white light applications. The important optical and physical properties of the studied NKLB-Dy glasses were determined. Judd-Ofelt (JO) parameters (Ωλ, λ = 2, 4, 6) were calculated for prepared glasses using the JO-theory. The radiative properties of the glasses were investigated using JO-parameter (Ωλ), refractive index (n) and emission spectra for all concentration of Dy2O3 in NKLB glasses. Moreover higher value of Ω2 and yellow to Blue (Y/B) ratio for title NKLB-Dy glasses confirm higher degree of covalency of Dy–O bonding. The CIE color coordinates for various concentrations fall in white region and CCT value for present NKLB-Dy glasses are more than warm (CCT = 4687K) The experimental lifetime decreases with increasing Dy2O3concentration. The non radiative energy transfer through resonance transfer (RET) and cross relaxation are the predominant causes of non-exponential behavior of the lifetime. The non-radiative decay rate (Wnr) has negative value for all NKLB-Dy glasses due to higher experimental lifetime than radiative lifetime. All these results suggest the potential use of studied NKLB-Dy glasses in various photonic devices application such as white light generation.

Synthesis and photoluminescence study of Dy3+ activated SrAl12O19 phosphor

Dy3+ doped SrAl12O19 phosphors, capable of radiating white light, were successfully synthesized via combustion method. Phase identification, morphological observations and elemental examination were done by employing X-ray diffraction, Field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The peaks in the X-ray diffraction patterns are found to be indexed well with the hexagonal phase (JCPDS card number 80-1195). Under 350 nm of excitation wavelength, the PL emission bands were peaking at 478 nm and 573 nm, which can be ascribed to the intra-4f transition of Dy3+. The emission data were analyzed for determining the CIE chromaticity coordinates and the correlated color temperature (CCT). A cool white light with chromaticity coordinates x = 0.3098 and y = 0.3538 and correlated color temperature of 6542 K was achieved for 3 mol% at 350 nm excitation. These results indicate that SrAl12O19:Dy3+ have practical applications in UV-pumped white light emitting diodes.

Processing thin, dense, transparent Ce:Y3Al5O12 films from flame made nanopowders for white light applications

Flame made metal oxide nanopowders enable processing of dense, transparent thin (< 50 μm) films of Ce3+ doped Y3Al5O12 for white light applications. The addition of very small amounts of SiO2 (0.14 wt. %) and the use of a final 95:5 N2:H2 atmosphere sintering step permits nearly complete removal of pores from films originally sintered in O2. Furthermore, the introduction of this final step allows reduction in processing temperatures needed to effect Ce4+ reduction to Ce3+ by several hundred degrees below typical temperatures of >1600 °C. At 20–50 μm, the reported films are also much thinner than previously reported for the same materials normally produced by solid state reactions of micron size powders. Spectrofluorometric measurements of the dense transparent films exhibit excitation spectra centered around 450 nm and broad emission spectra in the 470–750 nm range with two peaks centered at 537 and 570 nm, confirming their applicability as a phosphor for white light emitting diodes.

Physical, optical and luminescence properties of the Dy3+doped barium borophosphate glasses

Barium borophosphate glasses doped with dysprosium oxide had been fabricated by conventional melt quenching technique using the chemical composition of: (25BaO: 5B2O3: 70-xP2O5: xDy2O3)), where (x = 0.2, 0.4, 0.6, 0.8 and 1.0, mol%) (BaBPDy). The physical, optical and luminescence properties are studied for possibility of using as a white luminescence materials for solid-state light emitting devices. Judd-Ofelt (JO) theory is applied to study the radiative properties of the luminescence level of Dy3+ ions. The effect of the concentration quenching due to increase in Dy3+ ions is discussed in details. The lifetime of all BaBPDy concentration glass is bi-exponential in nature, which is discussed in the present work. This non-exponential nature of the decay curve was fitted by using the well-known Inokuti-Hirayama (IH) model S= 6, indicating that the energy transfer process is dipole-dipole type. The chromaticity co-ordinate(x, y) is evaluated from the luminescence spectra and its possibility for using as a white light application has been analyzed.

Synthesis and Photoluminescence Properties of Eu3+-Activated Double Perovskite Ba2YTaO6 Red Phosphor

In this study, Ba2Y1−xTaO6:xEu3+ (BY1−xT:xEu3+; x = 0.03–0.20), as a double perovskite orange-red-emitting phosphor, was synthesized by solid-state reaction. The prepared phosphor samples were characterized by XRD, SEM, photoluminescence spectra, temperature-dependent photoluminescence spectra and decay curve measurements. The X-ray diffraction patterns indicated that the phosphor is a pure phase of a double perovskite structure [space group Fm-3m (225)]. Upon near-ultraviolet excitation, the sample exhibited a strong orange-red emission at 592 nm due to the 5D0 → 7F1 transition, which revealed that the Eu3+ ions were located at the central symmetric lattice position. The critical concentration of Eu3+ ions in Ba2YTaO6 (BYT) was determined to be 12 mol.%. The as-prepared phosphors showed excellent thermal stability according to temperature-dependent emission spectroscopy. The CIE values of BY1−xT:xEu3+ phosphors were found to be located in the red region. These results suggested that the prepared BY1−xT:xEu3+ phosphors will have a potential application in white light emitting diodes (WLEDs).

Single phased white light emitting Dy3+/Sm3+ co-doped CePO4 nanocrystals for white light applications

Excitation dependent color tunable dysprosium and samarium co-doped cerium phosphate nanocrystals were synthesized via sol gel method. X-ray diffractograms confirmed that all the samples crystallized in monoclinic form. Morphology of the samples resembling a custard apple surface was demonstrated by FESEM analysis. The structural characterization carried out via FTIR and XPS analysis displayed the monoclinic CePO4 lattice as a good host providing minimum quenching environment. Luminescence characterizations were done in detail as a function of Dy3+ and Sm3+ doping concentrations by means of photoluminescence spectroscopy. Energy transfer from Ce3+ to Dy3+ and Sm3+ in CePO4 was established via the analysis of excitation spectra. The possibility of simultaneous activation of Dy3+ and Sm3+ ions was utilized to generate white light. Excitation dependent luminescence measurements were also carried out to explore the yellow-white-orange- red color tunability of synthesized samples for different excitations. The codoping of Sm3+ with Dy3+ is found to be more suitable for generating white light with CIE values close to the standard white and stands as a potential candidate in the field of white light applications.

A novel Ba4Gd3K3(PO4)6F2:Eu2+ blue-white emitting phosphor for near-ultraviolet excited light-emitting diodes

Exploring new phosphors with broadband emission could find potential applications in white light emitting diodes (w-LEDs). However, it is still a severe challenging to achieve a broadband emission in single activator doped phosphors. Herein, we reported a novel apatite-type Ba4Gd3K3(PO4)6F2:Eu2+ phosphor with broadband blue-white emission, which almost cover the whole visible light range. Differing from previous reports, we prove that the broadband emission is originated from the accommodation of Eu2+ ions in the M(1), Gd(2) and K(3) sites, respectively. Emission spectrum and luminescence decay curves further confirm the existence of three emission centers in Ba4Gd3K3(PO4)6F2:Eu2+ phosphor. White LED (Ra = 81 and CCT = 3780K) can be obtained by depositing Ba4Gd3K3(PO4)6F2:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors on 395 nm LED chip. Moreover, the as-obtained Ba4Gd3K3(PO4)6F2:Eu2+ phosphor can give an stable color output at high temperature, demonstrating that this novel phosphor could be an potential candidate for next-generation near ultraviolet excited white LEDs.

Optical Characteristics of Dy3+ Ions in Alkali Fluoroborate Glasses for WLEDs

The aim of this study is to synthesize and characterize an economical alkali fluoroborate glass doped with Dy3+ ions using melt quenching technique for white light generation applications. The glasses under investigation are prepared from the precursor mixture keeping the molar composition 10K2O + 10BaO + 10ZnF2 + (70-x)B2O3 + xDy2O3, where x = 0.1 mol.%, 0.5 mol.%, 1.0 mol.%, 1.5 mol.% and 2.0 mol.%. Optical characterization techniques such as absorption, photoluminescence excitation, emission and decay analysis were accomplished to validate the use of the prepared glasses for white light emitting diodes. Optical band gap energy and vital Judd–Ofelt (JO) intensity parameters were derived using the absorption spectrum. The JO intensity parameters were used to explore some characteristic radiative parameters of the present glass system. The photoluminescence spectra of the glasses have been recorded at an excitation wavelength of 348 nm and the spectra contain two intense emission bands in the blue (480 nm) and yellow (572 nm) regions and a weak band in the red region (664 nm). With the increase of dopant ion concentration, the intensity of all emission bands marked a gradual increase. The variation of the ratio of integrated intensity of yellow band to blue band (Y/B ratio) with the concentration of Dy2O3 is also studied. Color coordinates determined using commission international de l’eclairage (CIE) 1931 suggest that the prepared glass can be a potential material for white light applications. The experimental lifetime values marked a significant decrease with increase in dopant ion concentration and the mechanism responsible for the quenching is identified. Quantum yield is determined experimentally as well as using JO theory.

Temporal evolution of white light emitting CdS core and Cd1-xZnxS graded shell quantum dots fabricated using single step non-injection technique

White light emitting quantum dot (WQD) materials are being investigated due to their possible applications in the light emitting devices as single layer white light emitters and these have major advantage of lower re-absorption and self-absorption over multilayer emitters of different sized quantum dots (QDs). In this paper, white light emitting CdS core and Cd1-xZnxS graded shell based quantum dots have been synthesized using a single step non-injection technique. Detailed analysis of optical and structural properties has been carried out with QDs growth time. The photoluminescence (PL) consists a narrow band edge emission and a broad (in the range of 440–800 nm) trap state emission which results in white light emission and the quantum efficiency (QE) improves from ∼12% to 34% as growth time increases from 5 min to 30 min. The average fluorescence lifetime of band edge emission and trap state emission varies in the range of ∼2–5 ns and ∼250–550 ns respectively with QDs growth time. We have obtained a series of white light whose color coordinates are very close to the standard white light (CIE-1931); hence these QDs can be a good candidate for white light applications.

Luminous efficiency enhancement of WLEDs via patterned RGB phosphor arrays

Abstract Phosphor layer are essential in the application of phosphor-converted white light emitting diodes (pc-WLEDs). However, the conventional structure of red–green–blue (RGB) phosphor layers can cause severe re-absorption of blue light, resulting in low luminous efficiency and colour rendering index (CRI). In this paper, we fabricated a new WLEDs phosphor layer, which consisted of patterned RGB phosphor pixel arrays in a planar configuration, by the stencil printing technique. Optical simulation based on Monte-Carlo theory has been applied to assist designing the optimal pattern of the phosphor pixel arrays. By tuning the layout of the pixel arrays and the size of phosphor pixels, we achieved uniform output white light with high luminous intensity of 1.47 × 109 cd and CRI of 95.6, which are superior compared with the intensity of 1.11 × 109 cd and CRI of 93.5 obtained from WLEDs with conventional dispensing phosphor layer. Our newly-designed phosphor pixel-array layer possesses great potential for applications in advanced lighting and display devices with vast implications for industrial improvement in these research areas.

Photoluminescence and thermoluminescence studies of 100 MeV Si8+ ion irradiated Y2O3:Dy3+ nanophosphor

This paper reports on swift heavy ion (SHI) induced defects that were correlated to the color tuning in Dy3+ activated Y2O3 nanocrystals for possible application in white light emitting diodes and high energy dosimetry. The optimum concentration of trivalent dysprosium (Dy3+) doped with yttrium oxide (Y2O3) was prepared by the solution combustion technique. X-ray diffraction results revealed that the obtained powder material is a single phase body center cubic structure. The transmission electron microscopy images revealed that the particles were irregular shape with an average size of 37 nm. The composition of the synthesized materials were confirmed by Fourier transformed infra-red transmittance and Raman spectroscopy. The Dy3+ doped Y2O3 upon illumination with ultraviolet light showed the characteristic greenish yellow emission of Dy3+. This greenish yellow emission was enhanced when it was exposed to 100 MeV swift Si8+ ions and the ratio between yellow and blue emission could be tuned. This is ascribed to the SHI induced electrons/holes traps and the energy transfer between the electron/hole recombination centers and activator states in the host. The life time enhancement was found to be 931.55 μs and the photometric characterization showed that SHI influences the phosphor material to achieve pure white emission for light emitting diode applications at and beyond a fluence of 1 × 1011 ions cm−2. Thermoluminescence (TL) glow curves of 100 MeV Si8+ ion irradiated samples showed three glows with peaks at 408, 467and 592 K. The prominent peak (408 K) intensity increased upto a fluence of 1 × 1011 ions cm−2. TL trapping parameters were calculated using glow curve deconvolution (GCD) technique and the obtained results are discussed in detail.

C.10.02 Conceptualisation and treatment of schizophrenia negative symptoms: Can we do better?

Exploring new phosphors with broadband emission could find potential applications in white light emitting diodes (w-LEDs). However, it is still a severe challenging to achieve a broadband emission in single activator doped phosphors. Herein, we reported a novel apatite-type Ba4Gd3K3(PO4)6F2:Eu2+ phosphor with broadband blue-white emission, which almost cover the whole visible light range. Differing from previous reports, we prove that the broadband emission is originated from the accommodation of Eu2+ ions in the M(1), Gd(2) and K(3) sites, respectively. Emission spectrum and luminescence decay curves further confirm the existence of three emission centers in Ba4Gd3K3(PO4)6F2:Eu2+ phosphor. White LED (Ra = 81 and CCT = 3780K) can be obtained by depositing Ba4Gd3K3(PO4)6F2:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors on 395 nm LED chip. Moreover, the as-obtained Ba4Gd3K3(PO4)6F2:Eu2+ phosphor can give an stable color output at high temperature, demonstrating that this novel phosphor could be an potential candidate for next-generation near ultraviolet excited white LEDs.

Photoluminescence properties and energy transfer in a novel Sr8ZnY(PO4)7:Tb3+,Eu3+ phosphor with high thermal stability and its great potential for application in warm white light emitting diodes

Energy transfer from Tb3+ to Eu3+ was observed and verified in a warm white light emission phosphor SZYP:Tb3+,Eu3+ with high thermal stability.

Synthesis and luminescence properties of novel Eu2+/3+, Ce3+ ion single- and co-doped BaZn2(PO4)2 phosphors for white-light applications.

A series of novel Eu2+/3+, Ce3+ ion single- and co-doped BaZn2(PO4)2 samples were prepared via a high-temperature solid-state reaction. XRD powder diffraction results indicated that all of the products were pure phases. The photoluminescence properties of BaZn2(PO4)2:Eu showed that Eu2+ and Eu3+ coexist in the system and Eu3+ can be self-reduced to Eu2+ in an air atmosphere. In addition, the strongest emission peak of Eu3+ ions at 593 nm implied that Eu3+ ions occupy the inversion symmetry lattice and also the site of Zn in BaZn2(PO4). We used the theoretical method of bond energy to explain why the self-reduction of Eu3+ to Eu2+ can occur in the BaZn2(PO4)2 system. The calculation results indicated that the bond energy change value is smaller than , indicating that Eu2+ ions are more likely to occupy the Zn site and more stable than Eu3+ ions in BaZn2(PO4). Furthermore, the energy transfer process between Ce3+ and Eu2+ ions in the photoluminescence spectrum and the decay lifetime were observed, and the energy transfer mechanism was determined to be a dipole–dipole interaction. In this work, by adjusting the ratio of Ce and Eu ions, the emission color can be changed from blue to white, implying that the phosphor can be used as a promising candidate in the manufacture of white LEDs.

Synthesis of Longer‐Wavelength‐Emissive Carbon Quantum Dots for WLEDs and Investigation of Their Photoluminescence Properties

AbstractThe synthesis of highly fluorescent longer wavelength emissive carbon quantum dots (CQDs) is still a great challenge as well as an important issue, hindering its application in white light emitting diode (WLED). Herein, we have demonstrated a simple one‐pot solvothermal route for the synthesis of nitrogen and sulphur co‐doped CQDs using pyromellitic acid (PA), diethylenetriamine (DETA) and thiourea. At the specific molar ratio of the precursors, the orange color emissive CQDs (O‐CQDs) are synthesized and possess longer wavelength emission (611 nm). Additionally, O‐CQDs exhibits temperature and pH dependent photoluminescence (PL) properties. The O‐CQDs shows color correlated temperature (CCT) of 1745 K with high color purity of 98%. Simultaneously, as‐synthesized nitrogen and sulphur co‐doped CQDs shows concentration‐dependent PL properties, which display not only the brightness with stable orange color but also possess range of multicolour emission at different PL excitation. Solid host matrix of O‐CQDs is fabricated with poly‐(methyl methacrylate) (PMMA) chloroform solution and orange emissive property is investigated by wrapping the film over LED (InGaN) bulb. These studies will open up new opportunities to explore the tunable optical properties of carbon quantum dots and its applications in WLED devices.

Luminescence and energy transfer studies of Ce3+/Dy3+ doped fluorophosphate glasses

The fluorophosphate (PKABfNf:P2O5+K2O+Al2O3+BaF2+NaF2) glasses doped with single and co-doped (Ce and/or Dy) were prepared by conventional melt quenching technique and characterized their luminescence properties. The emission spectra of co-doped glass (PKABfNfCeDy) showed a broad blue band of Ce3+ ions combined with the sharp peaks of Dy3+ ions. Judd-Ofelt (JO) intensity parameters have been obtained from the optical absorption spectra of 1.0 mol% of Dy3+ (PKABfNfDy1.0) glass. JO theory has been used to find the radiative properties of PKABfNfDy1.0 glass by using Futchbauer-Ladenbergh formula. The (Ce3+/Dy3+) co-doped glass exhibit radiative energy transfer (ET) from Ce3+ to Dy3+ upon UV excitation and then intensity is increased with increase in Dy3+ ion concentration. The ET mechanism from Ce3+ to Dy3+ ion has been analyzed. The theoretical ET efficiency and quantum yield values were calculated from the emission spectrum of the Ce3+ and (Ce3+/Dy3+) co-doped glasses. These results suggest that the co-doped PKABfNfCeDy glasses are promising candidate for commercial white light applications.

Near-ultraviolet excited Tm3+ and Dy3+ ions co-doped barium lanthanum silica oxide phosphors for white-light applications

Nowadays, trivalent rare-earth ions activated inorganic luminescent materials have been widely investigated owing to their important applications in solid-state lighting field. Tm3+ and Dy3+ ions single- or co-doped Ba3La6(SiO4)6 (BLSO) phosphor materials for white light application were synthesized by a citrate-based sol-gel method. The prepared samples were examined by X-ray diffraction (XRD), scanning electron microscopy and Fourier-transform infrared spectroscopy to analyze the phase purity, surface morphology and existence of functional groups, respectively. The XRD pattern confirmed that the BLSO host lattice exhibited a hexagonal crystal structure with P63/m (176) space group, which is well indexed with standard JCPDS data. From photoluminescence results, the BLSO:Tm3+ phosphors exhibited purplish blue emission at 453 nm (1D2→3F4) and the BLSO:Dy3+ phosphors showed predominant yellow emission at 575 nm (4F9/2 → 6H13/2) compared to their shoulder blue emission at 479 nm (4F9/2 → 6H15/2), indicating that the Dy3+ ions occupied lattice sites with low inversion symmetry. The determined Commission Internationale de I’Eclairage (CIE) (0.3391, 0.3302) values for the Tm3+/Dy3+ co-doped BLSO phosphors were near to the standard sun light CIE values (0.33, 0.33) under near-ultraviolet (364 nm) excitation. The energy transfer process from Dy3+ to Tm3+ ions was discussed and it was proved by their corresponding decay curves. Additionally, thermal study was carried out for the optimized phosphor and it maintained superior thermal PL properties.

K3YB6O12:Sm3+: A novel orange-red emitting phosphor for white light emitting diodes

A series of novel orange-red emitting phosphors K3Y1-xSmxB6O12 (x = 0.005, 0.01, 0.02, 0.03, 0.05, 0.07, and 0.1) were synthesized via high temperature solid-state reaction. Their phase purity, crystal structure, photoluminescence property and decay behavior were investigated in detail. XRD results indicated the as-prepared phosphors were single-phases and crystallized in trigonal structure. Upon excitation with 403 nm, the phosphors emitted orange-red emission, which was ascribed to the 4G5/2→4HJ (J = 5/2, 7/2, 9/2, 11/2) transitions of Sm3+. The optimal doping concentration of Sm3+ ions in K3YB6O12 was about 0.05, beyond which the electric dipole-dipole interaction between Sm3+ and Sm3+ induced the luminescence quenching of Sm3+. The results showed that the orange-red emitting phosphors K3YB6O12:Sm3+ may have potential application in white light emitting diodes.

Synthesis and luminescence properties of Eu3+ and Dy3+ ions single and co-doped Ba2LaV3O11 phosphors for white-light applications

We report the synthesis and luminescence properties of the rare-earth ions doped Ba2LaV3O11 phosphors. The Dy3+ and Eu3+ ions single doped and Dy3+/Eu3+ ions co-doped Ba2LaV3O11 phosphors were synthesized via a citrate-based sol-gel method. The surface morphology, phase purity, photoluminescence properties and thermal stability of the synthesized phosphors were determined from the X-ray diffractometer, field-emission scanning electron microscope and spectrofluorometer, respectively. The obtained results indicate that the prepared phosphor material was crystallized in monoclinic phase with the space group P21/c (14) and the diffraction peaks were well matched with the standard JCPDS (#40-0105) card values. Under charge transfer band excitation wavelengths, the Eu3+ (277 nm) and Dy3+ (274 nm) single doped phosphor samples exhibited characteristic red and yellow emissions, respectively. Meanwhile, the Dy3+/Eu3+ co-doped phosphor samples showed near white-light emission.