Phosphors For Use Research Articles

Construction and characterization of an inorganic–organic hybrid copper(i) iodide coordination polymer with semiconducting luminescence

Inorganic–organic hybrid semiconductors based on copper(i) halide are intriguing luminescent materials possessing great prospects as rare-earth elements (REEs) free phosphors for use in solid-state lighting (SSL).

First-Principles Analysis of the Effects of Covalency and Ionicity on the 4f-5d Transition Energy of Ce3+ in Garnet-Type Oxides

Abstract A blue light-emitting diode (LED) and a yellow phosphor are frequently combined to create white LEDs, with (Ce3+)-doped YAG as a common phosphor utilized in this process. Yellow light is produced when Ce3+ ions, excited by blue LEDs, are combined with direct blue light to form white light. This study investigated the effects of electronic characteristics, such as covalency and ionicity, on the 5d and 4f level energies of Ce3+ in garnet-type crystals using relativistic discrete variational-Xα (DV-Xα) molecular orbital (MO) calculations. The purpose of this study is to elucidate a detailed mechanism for the centroid shift of the 5d level energies of Ce3+ in crystals based on the MO theory. The theoretical 4f-5d transition energies agreed well with experimental ones, and electronic structure analysis revealed a high correlation between the centroid shift and the net charge of Ce3+. The primary cause of the centroid shift of the 5d level energies relative to the lowest 4f level of Ce3+ in crystals is an increase of the 4f level energies caused by a reduction of the net charge of Ce3+. These results provide a theoretical foundation for the creation of novel Ce3+-doped garnet phosphors for use in displays and solid-state lighting.

Spectroscopic characterizations and investigation of Judd-Ofelt intensity parameters of Dy3+-doped Ba2La8(SiO4)6O2 near white light emitting phosphor

A series of Dy3+-activated Ba2La8(SiO4)6O2 phosphors were synthesized using the solid-state method with the objective of developing single host white light emitting phosphors for use in solid state lighting applications. The Dy3+ concentration varied between 0.01 and 0.05 mol%. The as-prepared phosphors crystal structure, optical, and photoluminescent properties (PL), along with energy transfer mechanism and luminescence decay, were investigated. The production of a single-phase Ba2La8(SiO4)6O2 with hexagonal symmetry was verified by the findings of the X-ray diffraction analysis. When the Ba2La8(SiO4)6O2: Dy3+ phosphors are exposed to ultraviolet light, they emit the characteristic yellow PL emissions caused by the 4F9/2 → 6H13/2 transition. The Judd-Ofelt (J-O) parameters (Ω2, Ω4, Ω6) were computed using the excitation spectra. The characteristics of the Dy3+ transition indicate that the asymmetric environment around the ligand was suggested by the trend, which was followed by J-O parameters. Due to the dominance of the electric-dipole transition in the luminescence spectrum, the Ba2La8(SiO4)6O2:0.03Dy3+ phosphor displayed yellowish white emission with CIE coordinates of (0.358, 0.398) and a CCT of 4724 K. The synthesized phosphor may be a useful material in the fabrication of white-emitting phosphor for LEDs application.

Spectroscopic characterization of Eu3+-doped KSrYSi2O7 phosphor for NUV LEDs: Estimation of the Judd Ofelt parameter

In this study, a series of Eu3+-doped KSrYSi2O7 phosphors were synthesized by employing the conventional combustion method. Phase confirmation revealed that the synthesized phosphor had a monoclinic structure with the P21/m phase group. For studying the effect of doping on the bandgap, the effect has been observed by applying the Kubelka-Munk function. The emission profile of the synthesized phosphor was recorded by stimulation with radiation of 239 nm. The recorded profile reveals the characteristics of the Eu3+ ions, which are concomitant with the f-f transitions. In addition, studying the quenching phenomenon, optical transition parameters corresponding to the Eu3+ ions were estimated using the Judd-Ofelt theory to validate the local symmetry properties. The thermal stability of the synthesized phosphor was also thoroughly studied. The temperature-dependent emission spectra of the prepared phosphors revealed the good thermal stability of the present phosphors, with a high activation energy of around 0.24 eV. The excellent color purity of 90.4% and thermal stability, along with the Commission International del’Eclairage (CIE) coordinates of (x = 0.551 and y = 0.436), suggest the suitability of the phosphor for use in different light-emitting applications.

Synthesis, photoluminescent properties, and an insight into the Judd-Ofelt analysis of the NaPbBi(2-x)(PO4)3: xEu3+ orthophosphate phosphors for light applications

A set of novel reddish orange light emitting NaPbBi2(PO4)3: xEu3+ (hereafter referred to as NPbBP) phosphate phosphors were synthesized by the conventional solid state reaction route. The phase formation, particle morphology, elemental composition and the optical properties of the prepared phosphors were studied in detail from the powder XRD data, SEM images, EDS analysis, and the diffuse reflectance spectroscopy measurements respectively. The photoluminescence properties were systematically studied by recording the excitation and emission spectra of the prepared phosphors. The NPbBP: xEu3+ phosphors, excited at the near ultraviolet light, exhibited the reddish orange light emission in the visible region due to the dominance of magnetic dipole transition of the Eu3+ ions in the host. The details of the radiative properties were analyzed through the Judd- Ofelt intensity parameters, which were found to follow the trend of Ω2< Ω4. The thermal stability and the life time of the phosphors were investigated. The calculated photometric parameters of the NPbBP: 0.09Eu3+ phosphor suggested that the emission was found in the reddish-orange region with a high color purity and high quantum yield of 99.53% and 79.7% respectively. These results showed that the NPbBP: Eu3+ phosphor could serve as a good phosphor for use in various optoelectronic devices such as phosphor converted WLEDs, solar cells, and display panels.

Grain Size Distribution Analysis of Different Activator Doped Gd2O2S Powder Phosphors for Use in Medical Image Sensors.

The structural properties of phosphor materials, such as their grain size distribution (GSD), affect their overall optical emission performance. In the widely used gadolinium oxysulfide (Gd2O2S) host material, the type of activator is one significant parameter that also changes the GSD of the powder phosphor. For this reason, in this study, different phosphors samples of Gd2O2S:Tb, Gd2O2S:Eu, and Gd2O2S:Pr,Ce,F, were analyzed, their GSDs were experimentally determined using the scanning electron microscopy (SEM) technique, and thereafter, their optical emission profiles were investigated using the LIGHTAWE Monte Carlo simulation package. Two sets of GSDs were examined corresponding to approximately equal mean particle size, such as: (i) 1.232 μm, 1.769 μm and 1.784 μm, and (ii) 2.377 μm, 3.644 μm and 3.677 μm, for Tb, Eu and Pr,Ce,F, respectively. The results showed that light absorption was almost similar, for instance, 25.45% and 8.17% for both cases of Eu dopant utilizing a thin layer (100 μm), however, given a thicker layer (200 μm), the difference was more obvious, 22.82%. On the other hand, a high amount of light loss within the phosphor affects the laterally directed light quanta, which lead to sharper distributions and therefore to higher resolution properties of the samples.

Single‐Layer Sheets of Alkylammonium Lead Iodide Perovskites with Tunable and Stable Green Emission for White Light‐Emitting Devices

AbstractRecently, metal halide perovskites have attracted considerable interest as highly emissive phosphors for use in white light‐emitting diodes (WLEDs). In perovskites, the migration of halide anions between green‐emitting bromide (e.g., CsPbBr3) and red‐emitting iodide (e.g., CsPbI3) materials is one obstacle to application. Here perovskite WLEDs that do not suffer from the anion exchange problem are reported: this is done by developing green‐emitting single‐layer sheets of (RNH3)2PbI4 (R = C18H35–, C12H25–, and C8H17–) and uniting these with red‐emitting CsPbI3 perovskite quantum dots (QDs). It relies on self‐assembly from ligand‐capped CsPbI3 nanocrystals to form single‐layer sheets of (C18H35NH3)2PbI4: via judicious selection of alkylamines and alkyl acids, (RNH3)2PbI4 single‐layer sheets that exhibit bright and stable green emission with well‐defined single‐layer thickness are produced. Emission from 505, 512 to 536 nm is tuned and a narrow (&lt;20 nm) linewidth is retained. Perovskite LEDs that produce white light with chromaticity coordinates (0.32, 0.33) and color gamut that reaches 117% National Television System Committee (NTSC) in the International Commission on Illumination (CIE) 1931 color space are demonstrated.

Rationalized crystal structure augmented highly efficient far-red-emitting double perovskite niobate phosphor for indoor plant growth LED applications

Since the inception of white light-emitting diodes (white LEDs), phosphor-coated LEDs have been in focus owing to the tremendous advantageous that they offer in assorted applications ranging from biomedical to automotive applications, including plant growth. While, plant growth LEDs have been bustling the commercial market, there is ample scope to commercialize the promising far-red (FR) emitting LEDs for potential growth of plants in indoor farming. Herein, a facile and efficient strategy was used to develop Mn4+ (Nb site)- and Sm3+ (La site)- ions-doped Ca2LaNbO6 (CLNO:Mn4+/Sm3+) phosphors with outstanding photoluminescence (PL) properties. The PL properties of CLNO:Mn4+ and CLNO:Sm3+ phosphors showed FR emissions at 650 and 697 nm, respectively. When Mn4+/Sm3+ ions were co-doped in a CLNO host lattice, Rietveld refinement revealed alterations in bond lengths of the CLNO crystal structure, which enhanced the phosphor’s thermal stability and photostability and caused the creation of effective pathways for efficient energy transfer from Sm3+ to Mn4+ ions. Furthermore, the reverse strategy, where the sensitizer (Sm3+) concentration was changed instead of activator (Mn4+) concentration, was used to achieve brilliant FR emission from the CLNO:Mn4+/Sm3+ phosphors and the dominant emission was perceived for the CLNO:0.2Mn4+/1.5Sm3+ phosphor. The internal quantum efficiency of the CLNO:0.2Mn4+/1.5Sm3+ phosphor was increased from 28% (CLNO:0.2Mn4+) to 56%. An LED fabricated by coating a CLNO:Mn4+/Sm3+ phosphor layer on a near-ultraviolet LED chip exhibited excellent FR emission with high color purity and with chromaticity coordinates of (0.733, 0.267). The results obtained for the CLNO:0.2Mn4+/1.5Sm3+ phosphor along with the characteristics of fabricated LED showed the high potential of the phosphor for use in promoting indoor plant growth.

MMCT-induced high-bright yellow light-emitting phosphor Bi3+-activated Ba2YGaO5 used for WLED

Based on the wide application of Bi3+-activated phosphors in Near-ultraviolet light-emitting diode (NUV-LED) chips for inducing healthy lighting, it is necessary to reveal the characteristics of high-quality Bi3+-activated phosphors. In this study, a high bright yellow light is realized with Bi3+-activated Ba2YGaO5, showing an Internal quantum efficiency (IQE) of up to 92%. Under 350 nm excitation, Ba2YGaO5: Bi3+ emits a broad yellow light peak at 587 nm with full width at half maximum (FWHM) of 135 nm, while simultaneously exhibiting good thermal stability; these results are superior to those of the commercial yellow phosphor Y3Al5O12: Ce3+. Moreover, significant cathodoluminescence properties are observed with Ba2YGaO5: Bi3+. These excellent luminescence properties are demonstrated to result from the D-level state described as the Metal-to-metal charge transfer (MMCT) state. Combined with the crystal and electronic structure of Ba2YGaO5, the origin of the D-level state along with its luminous mechanism is investigated in detail in this work, which may pave the way for developing more high-quality Bi3+-activated phosphors for use in NUV-LED chip-induced healthy lighting.

A novel narrow band blue-emitting phosphor Rb2ZrSi3O9: Eu2+ with low thermal quenching and high quantum efficiency

Developing phosphors with narrow band emission and excellent performance is the main goal of current leading research. In this study, a novel narrow band blue-emitting phosphor Rb2ZrSi3O9: Eu2+ was prepared that can be fully excited by near ultraviolet (NUV) light, emits a bright blue light peak at 470 nm, and has a full width at half maximum (FWHM) of 60 nm. The synthesized Rb2ZrSi3O9: Eu2+ had excellent photoluminescence properties that were reflected in its good thermal stability (up to 82%) and high internal quantum efficiency (up to 75%). These remarkable luminescence properties were mainly ascribed to the highly symmetric and dense crystal structure composed of [Si3O9]6- ring pairs. Multiple emission centers in the Rb2ZrSi3O9: Eu2+ phosphor were confirmed through the photoluminescence (PL) spectra and time-resolved (PL) spectra. A bright warm WLED device with a low correlated color temperature (3386 K) and high color-rendering index (CRI~89.3) was produced by combining the blue phosphor with (Sr, Ba)2SiO4: Eu2+ and CaAlSiN3: Eu2+ and NUV (380 nm). The results indicate that Rb2ZrSi3O9: Eu2+ could be a promising phosphor for use in WLEDs.

Encapsulating carbon quantum dot and organic dye in multi-shell nanostructured MOFs for use in white light-emitting diode

Abstract Encapsulating luminescence units into porous metal-organic frameworks to obtain white-light emission has attracted much attention because of their high designability and excellent color-tuning flexibility. In this study, two types of luminescence units with different emission color coverage, namely green-emitting carbon quantum dots (CQDs) and red-emitting rhodamine B (RhB) molecules, were encapsulated into porous ZIF-8 to obtain the yellow-emitting composite phosphor for use in white light-emitting diodes (LEDs). Single-phase single-shell CQDs&RhB@ZIF-82, as well as single-phase multi-shell CQDs@ZIF-82@RhB@ZIF-82, were fabricated and fine-tuned (by varying the amount of accommodated CQDs and RhB) so that the emitted color is near that of the commercial yellow-emitting phosphor. The multi-shell CQDs@ZIF-82@RhB@ZIF-82 has much better luminescence efficiency than that of the single-shell one. This is because the multi-shell structure provides a much larger separation distance of the encapsulated guest units, diminishing the energy-transfer-caused efficiency decrease. It is also shown that a bright source of white light can be realized by coating the CQDs@ZIF-82@RhB@ZIF-82 nanocomposite on a commercial blue (460 nm) LED chip.

Crystal structure, dielectric and optical properties of β-Ca3(PO4)2-type phosphates Ca9-xZnxLa(PO4)7:Ho3+

A series of new phosphates Ca9-xZnxLa(PO4)7:Ho3+ with the β-Ca3(PO4)2-type structure was synthesized by the solid state route. An intense near infra-red (NIR) emission according to intraconfigural 4f-4f transitions of Ho3+ ions 5I7 – 5I8 (~2 μm) and 5I6 – 5I8 (~1.156 μm) was observed. The obtained phases were studied by a combination of methods including synchrotron powder X-ray diffraction, dielectric spectroscopy, second harmonic generation, differential scanning calorimetry, luminescence spectroscopy. The structure of Ca8ZnLa(PO4)7 was refined by the Rietveld method in centrosymmetric space group R3‾c. The Ca2+ → Zn2+ substitution in the M5 site leads to a transformation from polar R3c space group (x = 0 – 0.5) to centrosymmetric R3‾c space group (x = 0.6–1) and to the increased integral intensity of luminescence with maxima at x = 1. It was concluded that the crystal site engineering in the Ho3+-containing β-Ca3(PO4)2-type hosts offers a promising way to obtain new NIR phosphors for use in the creation of biocompatible bone tissue fillers.

Characterization of optically-stimulated luminescence properties by NaCl:Eu2+ crystal and the thermal response

In this paper, we report optically-stimulated luminescence (OSL) properties of Eu2+-doped NaCl single crystal as a candidate phosphor for use in near real-time radiation measurement and dosimetry. The crystal was grown by the vertical Bridgman–Stockbarger method. The obtained crystal shows a strong photoluminescence (PL) band peaking at 430 nm due to the parity-allowed 5d-4f transitions of Eu2+. After irradiating with X-rays, it demonstrates OSL also at 430 nm due to the Eu2+ ion acting as an emission center while stimulating by light (500 ± 30 nm). Compared with a commercial BaFBr:Eu2+ OSL detector, the sensitivity to X-ray dose is lower by about one order of magnitude. In addition, while the crystal is reused multiple times, the OSL response signal increases despite the same given radiation dose. The OSL decay curve can be decomposed into three exponential decay functions with the lifetimes of 0.6, 6.4, and 120.5 s, and the decomposition analyses revealed that only the intensity of intermediate component increases with the number of reused cycles. Further analyses with thermally-stimulated luminescence (TSL) revealed that the intermediate OSL component is related to a TSL glow signal originated from trapping centers having the activation energies of ~0.93 eV and ~1.27 eV and the frequency factors of ~7.52 × 108 s−1 and ~6.29 × 1011 s−1, respectively.

Synthesis and photoluminescent characteristics of Sm3+-doped Ba3(PO4)2 phosphor hierarchical architectures

Highly uniform, petal-like, 3D-structured Ba3(PO4)2 phosphors were fabricated by facile wet chemical aqueous solution route. The production mechanism of Ba3(PO4)2 petal structure was optimized using XRD and SEM analysis grown under various temperatures and reaction times. Phase transition of Ba3(PO4)2 from the hexagonal to rhombohedral occurred with increasing reaction temperature. The Rietveld refinement based XRD phase analysis demonstrated the successful formation of monophase Ba3(PO4)2. Later, Ba3(PO4)2 was doped with various amounts of Sm3+ ions and with charge balance by Li+ ions. Ba3(PO4)2: Sm3++Li+ samples at 0.06 mol of Sm3+ concentration displayed maximum luminescence intensity in response to 402 nm excitation. Increasing the Sm3+ content over the 0.06 mol, emission quenching behavior was observed and it was explained by Dexter’s theory. The chromaticity coordinates of the Ba3(PO4)2:Sm3++Li+ phosphor material were calculated to be (0.5558, 0.4380), suggesting that it will be a potential yellow phosphor for use in W-LEDs in combination with blue LEDs chips.

Design of a Bismuth-Activated Narrow-Band Cyan Phosphor for Use in White Light Emitting Diodes and Field Emission Displays

To overcome the problem that Bi3+-activated phosphors suffer from, it is an urgent need to realize narrow-band light emission of Bi3+-activated phosphors, which not only improves their luminescence...

Unraveling the Luminescence Quenching of Phosphors Under High-Power-Density Excitation

Laser-driven phosphor-converted white light sources have received great attention for next-generation high-brightness lighting and display technologies. However, luminescence quenching of down-conversion phosphors under high-power-density excitation severely restricts the luminous efficacy and light output of laser-driven lighting devices. Till now, the mechanism for the quenching, once assigned to thermal quenching, is still argued, making it difficult to select appropriate phosphors for use in laser lighting and displays. In this work, we identify the optical excitation quenching (a non-thermal quenching effect) rather than thermal quenching that dominates the luminescence loss of Ce3+ - and Eu2+ -doped phosphors under high-power-density excitation. The optical excitation quenching is mainly caused by the excited-state absorption (ESA), and the quenching rate is greatly dependent on the decay time of phosphors, evidenced by combining the experimental data with theoretical models. A critical parameter, named as optical excitation quenching behavior, is finally proposed to screen laser-driven phosphors.

New red phosphor ceramic K2SiF6:Mn4+

Abstract A new transparent ceramic phosphor for use in LED lighting has been fabricated. The previously reported and optimized narrow-emitting red phosphor, K2SiF6:Mn4+ (KSF), has been consolidated into a transparent ceramic phosphor for the first time, accomplished via hot-pressing the feedstock phosphor powder in a die under vacuum. KSF ceramics were fabricated with varying doping concentrations of Mn4+ and their properties studied. The absorption and emission spectra of the ceramics were identical to the feedstock phosphor powders and are ideal for LED lighting with strong absorption at 450 nm and narrow emission around 630 nm. The absorbance of the ceramics was directly proportional to the doping concentration. The ceramics were excited at various blue light fluxes and their emission intensities measured to study the effect of Mn4+ concentration on intensity-driven “droop” in the emission output. The ceramics with a lower Mn4+ doping were more efficient under higher light fluxes due to a decrease in Auger upconversion losses. KSF ceramics can allow a much longer path length of the diode light through the phosphor, as compared to phosphor-in-silicone, enabling the use of low optical absorption and the associated reduced activator concentration. The ceramics are measured to have a thermal conductivity of ~1.0 W/m-K, higher than that of phosphor-in-silicone or phosphor-in-glass. Several of these properties make KSF ceramics potentially desirable for use in white light LEDs. Greater thermal conductivity helps with heat dissipation, the lower surface area of the ceramic compared to the powder minimizes the environmental vulnerability of KSF, and the ability to lower the Mn4+ concentration reduces Auger recombination losses and mitigates the temperature rise, particularly at higher light flux.

A novel narrow-band blue-emitting phosphor of Bi3+-activated Sr3Lu2Ge3O12 based on a highly symmetrical crystal structure used for WLEDs and FEDs

Investigating highly efficient narrow-band emission phosphors that have strong excitation bands in the near-ultraviolet (NUV) region is the main goal of the present light-emitting diode (LED) research, especially for Bi3+-activated phosphors. The naked 6s and 6p electrons of Bi3+ are sensitive to the microenvironment, thus leading to broad emission bands, while most Bi3+-activated phosphors suffer from low absorption of NUV-LED chips. Here, we report on a narrow-band blue-emitting garnet-type phosphor of Sr3Lu2Ge3O12: Bi3+ that is available for NUV-LED chips; its full width of the half maximum (FWHM) is limited to 40 nm, which is comparative to rare earth-activated phosphors, such as commercial blue phosphor BaMgAl10O17: Eu2+ (FWHM ≈ 52 nm), and this phenomenon is extremely rare among most Bi3+-activated phosphors. The internal quantum efficiency (IQE) of Sr3Lu2Ge3O12: Bi3+ can reach 57%. Moreover, it is interesting to find that Sr3Lu2Ge3O12: Bi3+ also exhibits exalting cathodoluminescence properties and its narrow-band emission produces brilliant images with high color saturation. The significant luminescent properties of trivalent bismuth are ascribed to the compact and highly symmetrical crystal structure of Sr3Lu2Ge3O12; thus, the discussion of the structure-property relations for Bi3+-activated Sr3Lu2Ge3O12 is the most anticipated part of this work. The results pave the way for the design of better Bi3+-activated phosphors for use as white light emitting diodes (WLEDs) and field emission displays (FEDs).

Enhanced thermal quenching characteristic via carbon doping in red‐emitting CaAlSiN3:Eu2+ phosphors

AbstractEnhancing thermal quenching characteristic of phosphor for use in high power white‐light‐emitting diodes (wLEDs) is a significant materials challenge. To achieve this goal, a series of red‐emitting carbidonitride phosphors Ca0.992AlSiN3 − 4/3xCx:0.008Eu2+ have been synthesized by high‐temperature solid‐state reaction method. Crystal structure, luminescence properties, and thermal quenching process are investigated. The location of carbon in the lattice is proved by the Raman spectra. The preferential crystallographic site of carbon is validated by the first‐principles density functional theory calculations combining the Rietveld refinement. With carbon doping from x = 0 to x = 0.24, the emission spectra are blue‐shifted from 656.8 to 650.2 nm, and the fitted lifetime of Eu2+ decreases from 775.3 to 721.7 ns. Replacing nitrogen by carbon enhances thermal quenching characteristic by 8.9% at 300°C. Carbon doping enlarges the thermal ionization energy barriers (EdC) which is calculated at great length, and suppresses thermal ionization process. A wLED fabricated by the combination of a blue chip with the as‐synthesized red phosphor and LuAG: Ce3+ green phosphor shows a high color rendering indexes (Ra = 95.9 and R9 = 92). The promising application of Ca0.992AlSiN3 − 4/3xCx:0.008Eu2+ phosphor for wLEDs is proved by all results above.

Sol-Gel Synthesis and Photo-Luminiscence Study of NaSr1-xPO4:xDy3+ Phosphor for Use in PC-WLED

Sol-Gel Synthesis and Photo-Luminiscence Study of NaSr1-xPO4:xDy3+ Phosphor for Use in PC-WLED