White LED Applications Research Articles

Single-phase white light emission Ca9NaLu0.667(PO4)7: Eu2+, Mn2+ phosphor for the application of WLED

A single-phase full-spectrum emission Ca9NaLu0.667(PO4)7 (CNLP):Eu2+/Mn2+ phosphor was synthesized through the reaction to the solid state reaction at high temperature. CNLP:Eu2+ exhibits cyan light-emitting, and the luminous color of CNLP:Eu2+,Mn2+ has been adjusted from cyan then to white and finally to red by changing the content of Mn2+. The occupancy of Eu2+/Mn2+ was also analyzed by calculating the average bond length obtained using the Rietveld refinements. The energy transfer process (ET) of Eu2+ → Mn2+ was discussed in detail, and the ET efficiency could be as high as 77.81%. The internal quantum yield (QY) value of CNLP:2%Eu2+,3%Mn2+ is 49.51% at the excitation of 360 nm. CNLP:2%Eu2+,3%Mn2+ has a good thermostability. The white light-emitting diode (WLED) device showed warm white emission, which represented a low correlated color temperature (CCT) and high color rendering index (Ra). Moreover, the CCT and Ra remain within a certain range under different currents and temperatures, further demonstrating the potential application of WLEDs. These results prove that CNLP:2%Eu2+,1%Mn2+ phosphor has potential applications in the field of WLED.

Ultrastable FB@CsPbBr3/PMMA composites based on in-situ passivation and encapsulation for WLED applications

In this article, the in-situ passivation and encapsulation strategy of perovskite quantum dots (PQDs) is proposed using inorganic transparent host (FB, FIREBIRD) and PMMA， respectively. CsPbBr3 are deposited on the surface of FB and FB@ CsPbBr3 composites are obtained. Then FB@CsPbBr3 is coated with PMMA and FB@CsPbBr3/PMMA is prepared. The in-situ passivation and encapsulated CsPbBr3 is very stable in the moisture, heat, and irradiation environment due to the hydrophobic and thermal insulation layers. Meantime, the luminous efficiency of FB@CsPbBr3/PMMA is 70.96%. Furthermore, the white LED (WLED) device is fabricated by combining as-prepared FB@CsPbBr3/PMMA composites, FB@CsBrI2/PMMA composites and a blue LED chip. The Commission Internationale de I’Eclairage (CIE) color coordinates of the fabricated WLED is (0.29, 0.29). A color area of LED device is about 128% of the National Television Standards Committee or 99% of the Rec. 2020 standards. This work provides a novel in-situ passivation and encapsulated strategy through a combination of thin-film packaging and heat-insulating transparent materials which presents a new idea and solution for improving the stability of CsPbBr3.

Green synthesis strategy to construct strong zero-phonon line red emission phosphor Na2SiF6:Mn4+: Photoluminescence properties, thermal stability and application in warm white LEDs

Green synthesis strategy to construct strong zero-phonon line red emission phosphor Na2SiF6:Mn4+: Photoluminescence properties, thermal stability and application in warm white LEDs

Synthesis, Photoluminescent Characteristics and Eu3+-Induced Phase Transitions in Sr3Zr2O7:Eu3+ Red Phosphors.

Designing phosphors that are excited by blue light is extraordinarily important for white light-emitting diodes (w-LEDs). In the present study, a new Ruddlesden-Popper type of SZO:xEu3+ (x = 0.01~0.10) phosphors was developed using solid-state reactions. Interestingly, a Eu3+ doping-induced phase transformation from the Sr3Zr2O7 (cubic) to the SrZrO3 (orthorhombic) phase was observed, and the impact of the occupied sites of Eu3+ ions on the lifetime of Sr3Zr2O7:xEu3+ phosphors is discussed in detail. Diffuse reflectance spectroscopy results showed that the band gap of SZO:xEu3+ phosphors gradually increased from 3.48 eV for undoped Sr3Zr2O7 hosts to 3.67 eV for SZO:0.10Eu3+ samples. The fluorescence excitation spectrum showed that ultraviolet (300 nm), near-ultraviolet (396 nm) and blue light (464 nm) were all effective excitation pump sources of Sr3Zr2O7:xEu3+ phosphors, and the strongest emission at 615 nm originated from an electric dipole transition (5D0→7F2). CIE coordinates moved from orange (0.5969, 0.4267) to the reddish-orange region (0.6155, 0.3827), and the color purity also increased. The fabricated w-LED was placed on a 460 nm chip with a mixture of YAG:Ce3+ and SZO:0.1Eu3+ samples and showed "warm" white light with a color rendering index (CRI) of 81.8 and a correlation color temperature (CCT) of 5386 K, indicating great potential for application in blue chip white LEDs.

Downconverted significant luminescence enhancement and structural confinement of a dichromatic nanophosphor for potential applications in NUV-triggered cool pc-WLEDs

Trivalent rare-earth ions activated phosphor-converted near ultraviolet (NUV) triggered white light-emitting diodes (WLEDs) are nowadays being explored as a prominent light source, in the field of lighting. Herein, we prepared a sequence of single-phase Gd2O3:Dy3+,Li+nanophosphor via chemical co-precipitation techniques for the applications in cool pc-WLEDs. To examine the crystal structure, luminescent characteristics, and potential applications of WLEDs, a systematic and comprehensive analysis was conducted. This study extensively investigated the effect of Li+ on the Gd2O3:Dy3+white-emitting nanophosphor. The phase purity and crystal structure of nanophosphors were characterized via powder X-ray diffraction (XRD) analysis. Rietveld refinement clearly quantified that the Gd2O3 host possesses two non-equivalent cationic sites that are coordinated sixfold. The interior morphology and elemental composition were illustrated by high-resolution transmission electron microscopy (HR-TEM) and energy dispersive spectroscopy (EDS). These nanophosphors effectively exhibit dichromatic significant photoluminescence (PL) emission bands of Dy3+ ion for blue and yellow color at 486 and 574 nm, while triggered in the NUV range. The blending of blue and yellow color lights yields a broad spectrum of light that appears white color to the human eye. Besides, it has been observed that the incorporation of Li+ significantly enhances the PL-emission intensity. The critical distance between Gd3+ and Dy3+ was determined, and it showed that the electric multipolar interaction was responsible for the energy transfer quenching mechanism. The colorimetric performance reveals that the CIE coordinates fall within the white region of the color space and that the correlated color temperature (CCT) is substantially higher than 4000 K. The lowest color purity (CP) was found to be 4.0% for x = 2 at.%Li+ ion concentration under excitation wavelength 350 nm. These findings suggest that the prepared nanophosphors are a suitable candidate for application in NUV-triggered cool-WLEDs.

Realizing multicolor tunable photoluminescence in La2MgTiO6: Tb3+, Eu3+ phosphors via energy transfer and application for white light-emitting diodes

The achievement of multiple emission color phosphors has a significant importance in screen display, lighting devices, and multicolor imaging, but it still faces formidable challenges. In this work, double perovskite La2MgTiO6: Tb3+, Eu3+ phosphors with tunable emissions are designed and successfully synthesized. The obtained phosphors can emit intense green (Tb3+), red (Eu3+), and yellow emissions (Tb3+/Eu3+) via varying the co-doping concentration of Tb3+ and Eu3+. The CIE coordinates exhibit an excellent linear behavior in La2MgTiO6: Tb3+, Eu3+, revealing the possibility of linear adjustment of multiple emission colors. Detailed material characterization demonstrates that the multicolor tunable emission originates from energy transfer between Tb3+ and Eu3+. The decay dynamics analysis suggests that the multipole interaction between Tb3+ and Eu3+ is quadrupole-quadrupole interaction. A white light-emitting diode device with color rendering index of 84.7, correlated color temperature of 4684 K, and CIE coordinate of (0.3472, 0.3083) is fabricated by combining La2MgTiO6: Tb3+, Eu3+ yellow phosphor and BaMgAl10O17: Eu2+ blue phosphor. Our results reveal that La2MgTiO6: Tb3+, Eu3+ phosphors are promising luminescent materials in white light-emitting diodes.

Preparation and luminescence investigations of garnet-based Y2Ca2Ga3VO12:RE (RE = Eu3+, Sm3+, and Dy3+) phosphors

We report, for the first time, the preparation and luminescence investigations of the YCGVORE (RE = Eu3+, Sm3+, and Dy3+) phosphors. The efficient multicolor emissions at 592 nm (orange), 612 nm (red), and 577 nm (yellow) were obtained from YCGVO:RE (RE = Eu3+, Sm3+, and Dy3+) phosphors with near-UV excitation. The room temperature decay of 5D0 (Eu3+), 4G5/2 (Sm3+), and 4F9/2 (Dy3+) levels in YCGVO:RE phosphors exhibits the average lifetime of 2.59–2.89, 0.82–1.44, and 0.25–0.63 ms, respectively. Upon excitation of VO43- group, the emission intensity of the RE ions increases with increasing the dopant concentration, simultaneously, the intensity of 520 nm emission related to the VO43- group decreases, indicating an efficient VO43− → RE energy transfer (ET). The YCGVO: RE (RE = Eu3+, Sm3+, and Dy3+) phosphors are promising candidate for white LED application.

Novel Red‐Emitting Gd3BW1‐xMoxO9 : Eu3+ Phosphor with High Thermal Stability for Application in UV‐Excited WLEDs and Rapid Visualization of Latent Fingerprints

AbstractRare‐earth‐doped inorganic luminescent materials are widely used in white light‐emitting diodes (WLEDs), lasers and forensic sciences due to their outstanding optical characteristics. However, it is still a challenge to obtain such materials with better thermal stability for application in WLEDs on account of their serious thermal quenching properties. In addition, there is still room for improvement in some respects such as higher sensitivity and contrast for application in latent fingerprint development. Herein, a series of novel Gd3BW1‐xMoxO9 : Eu3+ phosphors have been synthesized via high‐temperature solid‐state reaction process. Compared with different Mo6+ ions doping concentrations, Gd3BW0.7Mo0.3O9 : Eu3+ phosphor has optimal photoluminescence properties. Meanwhile, the emission intensity of Gd3BW0.7Mo0.3O9 : Eu3+ phosphor is over 3 times higher than that of commercial red phosphor. More impressive is its excellent resistance against thermal quenching; when heated up to 150 °C, the Gd3BW0.7Mo0.3O9 : Eu3+ phosphor still preserves about 98 % emission intensity of that at room temperature. Furthermore, the latent fingerprints (LFPs) developed by Gd3BW0.7Mo0.3O9 : Eu3+ phosphor exhibited the excellent visualization on various nonporous substrates, and level 1–3 features were well identified with high contrast and sensitivity. The obtained results suggested that the as‐prepared phosphor has great potential for application in both WLEDs and latent fingerprint detection.

CuInS2 Nanocrystals Embedded PMMA Composite Films: Adjustment of Polymer Molecule Weights and Application in Remote-Type White LEDs.

The commercial application of colloidal semiconductor nanocrystals has been realized owing to the development of composite film technology. Here, we demonstrated the fabrication of green and red emissive CuInS2 nanocrystals embedded polymer composite films of equal thickness by using a precise solution casting method. The impacts of polymer molecular weight on the dispersibility of CuInS2 nanocrystals were then systematically studied through evaluating the decrease in transmittance and red shift of emission wavelength. The composite films made from PMMA of small molecular weights exhibited higher transmittance. Applications of these green and red emissive composite films as color converters in remote-type light-emitting devices were further demonstrated.

Fabrication, Optical Property, and White LED Application of Novel Lanthanide‐Based Family Cs2NaLnX6 (X = Cl, Br, I) Perovskite Nanomaterials

AbstractLead free double perovskites are highly promising optoelectronic materials, but most of them suffer from low photoluminescence quantum yield (PLQY) and poor stability. Herein, a series of lanthanide elements are used to prepare the lead free double perovskite Cs2NaLnX6 (X = Cl, Br, I) nanocrystals (NCs), acting as both the main structural ions and the 4f–4f emission centers. The mechanisms for the broadband emission of Cs2NaLnX6 NCs host are carefully studied based on various spectral results combining ultrafast dynamics detection and first‐principles calculation. The broadband emission of the Cs2NaLnX6 NCs originates from the self‐trapped exciton. The Cs2NaLnX6 NCs show remarkable water stability for more than eight months and favorable temperature and light irradiation stability (500 h). The PLQY for these materials is much higher than most of double perovskite materials, especially for Cs2NaEuCl6, which can approach to 70%. The white light emission from a single host material Cs2NaEuTbCl6 (Tb:Eu = 25:1) is obtained and applied to a light‐emitting diode device, with a good CIE (Commission International de L'Eclairage) coordinate of (0.334, 0.326) and color rendering index of 91.2. Overall, the characteristics of lanthanide ions endow the super performance of Cs2NaLnX6 NCs, which is obviously an important choice for future optoelectronic devices.

Polymer-doped perovskite nanocrystals for efficient single active layer white light-emitting diodes through energy transfer

White-light emitting diodes (WLEDs) are mainly constructed by stacking different light-emitting layers with complementary emission spectra. However, this not only requires complex device fabrication processes but also needs comprehensive charge transport regulation, limiting the development and application of WLEDs. In this work, efficient single-layer WLEDs are achieved via doping tiny amount of a red polymer poly[[9-(1-octylnonyl)-9H- carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 thiophenediy (PCDTBT8) into the perovskite nanocrystals (NCs) matrix. The 490 nm sky blue perovskite nanocrystals (FA0.08Cs0.92PbBr2Cl) are synthesized and passivated with a short-chain ligand 3-methoxyphenethylamine (MPEA), which enhances luminance and stability at high bias. Energy transfer from NCs to PCDTBT8 significantly enhances red-light emitting in the range from 600 to 750 nm, enabling white-light emission. By tuning of the NCs:PCDTBT8 weight ratio from 400:1 to 150:1, a continuous transition of emission from cold white-light to warm white-light is achieved. With the NCs:PCDTBT8 weight ratio of 250:1, a standard white-light emission with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.33, 0.33), a luminance of 752 cd/m2 and an external quantum efficiency (EQE) of 1.59% are obtained at a fairly low voltage of 4.8 V.

Synthesis and luminescence properties of Ca3Ga4O9:Eu3+: An efficient red-emitter for WLEDs

Herein we report, an efficient red-emitting phosphor Ca3Ga4O9:Eu3+ (Eu3+: CGO) was synthesized via a conventional solid-state reaction technique. The physicochemical properties of the given oxide phosphors were investigated in terms of structural, elemental, compositional, and optical characteristics. The XRD study indicates that the compound CGO and Eu3+: CGO have been crystallized in an orthorhombic crystal system with the space group of Cmm2. The nature of the oxidative state of the elements and their compositional ratios were demonstrated by the XPS and EDS studies. The SEM analysis of the phosphor samples reveals micro flakes embedded in rod-like morphology. UV–Visible diffuse reflectance studies were performed to study the optical properties of the oxide phosphors. The optical energy gap value has been calculated using Kubelka-Munk equations and the values have a reducing trend due to the addition of the Eu3+ ion. The photo-emissive properties of the Eu3+ doped samples were illustrated by the PL analysis with the excitations of 465 nm and 394 nm (7F0 -5D2 and 7F0-5L6) respectively. The photometric (color coordinates, color purity, and correlated color temperature) parameters were also calculated. The Eu3+ doped samples show a high color purity within the range of 96.75–98.71%. The correlated color temperature (CCT) was also computed from the calculations which have the values from 1819 K to 1898 K. These results depict that the prepared Eu3+ ions doped oxide phosphor will be an efficient red-emitting candidate for white LED application.

Hydrogen bonds and space restriction promoting long-lived room-temperature phosphorescence and its application for white light-emitting diodes

Achieving the long-lived and strong room-temperature phosphorescence (RTP) is challengeable but desirable, especially for the enhanced phosphorescence and metal-free nanomaterials. Herein, we initially synthesized the green-fluorescence carbon dots (pm-CDs), and further obtained the composite of pm-CDs@DCDA with a long RTP lifetime of 1.01 s through embedding pm-CDs in dicyandiamide (DCDA). And the bright and long-lived afterglow of pm-CDs@DCDA with 365 nm of UV light excitation was observed by the naked eyes for more than 17 s either emerging as the dry solid or in water. Importantly, the phosphorescence intensity and lifetime of pm-CDs@DCDA were remarkably promoted owing to the intermolecular hydrogen bonds and the rigid environment, hence facilitating the intersystem crossing (ISC) process and restricting the non-radiative transition of triplet excitons. Taking advantage of the superior solid-state luminescence of pm-CDs@DCDA, we further innovatively prepared the white light-emitting diodes (WLEDs) with the tunable color temperatures by regulating the mass of pm-CDs@DCDA coated on the chips. This proposed study originally employed DCDA as a matrix to separate and immobilize pm-CDs, which built up a new avenue to improve the RTP property and offered a promising application in WLEDs.

Excitation‐dependent energy transfer and color tunability in Dy3+/Eu3+ co‐doped multi‐component borophosphate glasses

AbstractUsing the melt‐quench technique, potassium zinc borophosphate (KZnBP) glasses incorporated with Dy3+, Eu3+, and Dy3+/Eu3+ ions individually and combinedly were prepared, and their photoluminescence (PL)‐related features were investigated. The KZnBP glass containing an optimized content of Dy3+ (0.5 mol%) is co‐doped with Eu3+ in various contents, and the energy transfer (ET) process between them was studied at λexci = 349, 364, 387 (Dy3+), and 394 nm (Eu3+). The Dy3+/Eu3+ co‐doped system, when excited with Dy3+ excitations has resulted in a significant decrease in the intensity of Dy3+ peaks observed at 480 nm (4F9/2→6H15/2, blue) and 574 nm (4F9/2→6H13/2, yellow), with simultaneous enhancement of the intensity of Eu3+ peaks at 591 nm (5D0→7F1, orange) and 617 nm (5D0→7F2, red). This trend is due to the efficient energy transfer from Dy3+ to Eu3+, indicating that Eu3+ ions were sensitized by Dy3+ ions. Dexter's theory and the Inokuti–Hirayama (I–H) model revealed that the dipole–dipole interaction is accountable for the energy transfer from Dy3+ to Eu3+ through energy‐transfer channels [4F9/2(Dy3+)+7F1,2(Eu3+)→6H15/2(Dy3+)+5D2(Eu3+)] and [4F9/2(Dy3+)+7F0(Eu3+)→6H13/2(Dy3+)+5D0(Eu3+)]. The color coordinates of the Dy3+/Eu3+ co‐doped glasses under various excitations fall within the white light emission spectrum, indicating their potential application in warm white LEDs.

Study of White Light Emission from Europium (III) Doped Gadolinium Oxide Phosphors

Gadolinium Oxide doped with various concentrations of Europium (III), were prepared using the solid-state reaction method. Sample with 1.5 mol% of Europium underwent the XRD characterisation to examine the phases available and to confirm the presence of proper phases in prepared samples. Observed XRD pattern exhibited significantly good resemblance with crystallographic open database card No. 96-101-1289, specifically reported for Gd2O3 with cubic structure and I 21 3 (199) space group. Prepared samples were studied using Photoluminescence (PL) emission spectra. The PL emission expressed various peaks centred at 470, 496, 515, 540, 550, 592 and 616 nm out of which peaks centred at 470, 496, 515, 540 and 550 nm were attributed to 6G11/2, 6G9/2, 6G5/2 6P7/2, peak centred at 592 nm is assigned to 6G7/2 6P7/2 whereas the peak centred at 616 nm may correspond 6G11/2, 6G9/2, 6G5/2 6P3/2 transitions. CIE coordinate was found as (0.40, 0.43) which is under the region described for white light emission. Correlated Colour Temperature (CCT) was estimated as 3853 K and Colour Rendering Index (CRI) was 61. Obtaining CRI in this range enabled us to conclude that emission received is satisfactorily good so far as its application in White LED is concerned.

Ce,Tb,Gd:YAG-Al2O3 eutectic crystal phosphor plates for high-power warm white LED applications

Ce,Tb,Gd:YAG-Al2O3 eutectic crystal phosphor plates (ECPPs) were grown by the micro-pulling-down (μ-PD) method to adjust correlated color temperature (CCT) and color rendering index (Ra) for high-power warm white LED applications. Tb3+ and Gd3+ ions in Ce:YAG-Al2O3 play a positive role in spectra adjustment based on the structural and luminescent properties investigations. Tb3+ ions enhance the fluorescence lifetime of Ce3+ ions from 61.1 to 63.8 ns and improve the luminescence efficiency, and the highest optical-optical conversion efficiency (OCE) is 270.56 lm/W. Corresponding luminescence shift from cold white to greenish yellow. Gd3+ ions increase the peak wavelength from 554 to 564 nm and improve the Ra value, and the maximum Ra is 75.5. Corresponding luminescence is shifted from cold white to reddish violet. In addition, the luminescence of Ce,Tb,Gd:YAG-Al2O3 ECPPs is adjusted to warm white with CIE coordinate (0.374, 0.364) and CCT of 4102 K, and Ra of 73.0, which is of great significance for realizing the high-power warm white LED lighting.

Novel Sm3+/Eu3+ co-doped Sr7Sb2O12 red-emitting phosphor for white LED

Novel red-emitting phosphors Sr7Sb2O12: Sm3+ and Sr7Sb2O12: Sm3+, Eu3+ were successfully synthesized through a high temperature solid-state reaction method. The materials were characterized by X-ray diffraction patterns, scanning electron microscopy, Raman spectra, diffuse reflection spectra, photoluminescence excitation and emission spectra, luminescence decay curves and temperature-dependent emission spectra. The energy transfer between Sm3+ and Eu3+ ions in Sr7Sb2O12 was realized via electric quadrupole–quadrupole interaction with about 42.4% transfer efficiency. The phosphor exhibited good thermal stability with activation energy of 0.180 eV. Color coordinates and color purity of Sr7Sb2O12: 0.08Sm3+, 0.09Eu3+ was (0.620, 0.368) and 87.4% respectively. Combined the red phosphor with the near-UV or blue chips, the fabricated light emitting diode (LED) lamp emitted white light with Ra = 83.7 or 82.4 color rendering index (CRI) respectively. These results demonstrated that Sm3+/Eu3+ co-doped Sr7Sb2O12 red phosphor has a great potential application in white LED.

Passivation of Surface Defects by X-type Short-Chain Ligands for High Quantum Yield and Stable CsPbX3 Quantum Dots Synthesis and Application in WLEDs

All-inorganic CsPbX3 perovskite quantum dots have excellent optoelectronic properties and are excellent candidates for optoelectronic applications. However, the surface ligands (oleyl ammonium, oleic acid) commonly used in traditional inorganic perovskite quantum dots easily fall off from the quantum dots and their protective power is relatively weak, resulting in poor quantum yield and stability of the quantum dots, limiting their application. In this paper, we introduce an X-type short-chain ligand (DDEAB) passivation strategy to enhance the optoelectronic properties of CsPbX3 quantum dots through a facile room-temperature synthesis method and the strong affinity of X-type ligands for surface atoms. The results of TRPL and X-ray photoelectron spectroscopy showed longer lifetime and stronger surface affinity. This result confirms that didecyldimethylammonium bromide (DDEAB) has better binding to CsPbBr3 QDs and can effectively reduce surface defects and improve quantum yield. As a result, the introduction of short-chain ligands can more effectively passivate the surface halogen defects of CsPbX3 QDs, achieving high quantum yield (>90%) and long-term storage environmental stability. In addition, DDEAB-passivated CsPbBr3 QDs have been successfully applied in white light emitting diodes (WLEDs) with wider color gamut (123%), and good EL stability compared to NTSC TV color standard. Our proposed short-chain ligand DDEAB passivation strategy may provide a reference guideline for the preparation of quantum dots and photovoltaic devices with high photoluminescence and environmental stability.

Strong energy transfer and color tunable emission in Eu2+ and Mn2+ co-doped Na2BaSr(PO4)2 phosphor

The new dual-emitting and color tunable single phase of Na2BaSr(PO4)2:0.03Eu2+, xMn2+ (NBSP:0.03Eu2+, xMn2+) phosphor are successful prepared in this work. The phase purity and photoluminescence properties are investigated. Regarding to the coordination, valence and cation radius, the Eu2+ ions occupy the Sr2 and Sr3 site and Mn2+ ions occupy the Sr3 site. According to the photoluminescence (PL) spectra of NBSP:0.03Eu2+, xMn2+ (x = 0–0.09), the strong energy transfer (ET) between Eu2+ and Mn2+ exists in these phosphors. The strong ET efficiency from Eu2+ to Mn2+ is as high as 92%, while the ET mechanism of Eu2+ and Mn2+ is quadrupole-quadrupole interaction. Moreover, the CIE coordinate of Eu2+ and Mn2+ co-doped Na2BaSr(PO4)2 phosphors can realize the color tunable emission from blue to cold white. The temperature dependent photoluminescence intensity of NBSP:0.03Eu2+, 0.05Mn2+ phosphor still keeps 75.8% of that initial intensity when the temperature is 150 °C. In summary, the NBSP:0.03Eu2+, xMn2+ phosphors have a promising application in white light LED.

Influence of K/Na ions on structure and luminescence properties of red phosphors K0.5Na0.5Gd(WO4)2: Eu3+

In this paper, we demonstrated the influence of K/Na alkali ions on the structural and photo-cathodoluminescence properties of novel K0.5Na0.5Gd(WO4)2:Eu3+ red phosphor synthesized by the solid-state method. The purity of phosphors is determined from the X-ray diffraction. Rietveld refinement studies confirms that the compounds both K0.5Na0.5Gd(WO4)2:Eu3+ and NaGd(WO4)2:Eu3+ were crystallized in the tetragonal structure with I41/a space group and KGd(WO4)2:Eu3+ was crystallized in monoclinic structure with C2/c space group. The FTIR results indicate that the presence of characteristic functional groups in synthesized samples. The optical bandgap determined from the UV-Visible reflectance spectra in the order K0.5Na0.5Gd(WO4)2:Eu3+ <KGd(WO4)2:Eu3+<NaGd(WO4)2:Eu3+. The photoluminescence excitation spectrum reveal that all the synthesized phosphors can be efficiently excited near UV and Ultraviolet (UV) indicating suitable for solid state display applications. The PL emission spectra indicate the two characteristic emissions located at 614 nm (5D0→7F1) and 590 nm (5D0→7F1) under the excitation of 395 nm. The Judd-Offelt (JO) intensity parameters are calculated to investigate the luminescence behavior and to determine the local structure around the activator related to the Eu3+ ion. The Ω2 > Ω4 of JO parameters indicates the asymmetric environment around the activator suggesting the co-valency of Eu-O bonds with respect to host matrix. Radiative lifetime, branching ratio, electronic dipole transition probabilities were calculated based on the Judd-Ofelt formalism. Cathodoluminescence studies shows the characteristic emission of the Eu3+ ions for low current and voltage which further confirms the pure red color emission of phosphors. All the synthesized phosphors can emit the red emissions with correlated color temperature range from 1500 to 2000 K. For K0.5Na0.5Gd(WO4)2:Eu3+ sample the chromaticity coordinate (x = 0.667, y = 0.329) are closer to the NTSC trichromatic coordinated (x = 0.67,y = 0.33) than that of Y2O2S:Eu3+ suggesting that K0.5Na0.5Gd(WO4)2:Eu3+ can be a potential red phosphor material for warm white LED's applications.