Near-ultraviolet LED Chip Research Articles

Ultrabroadband Long-Wavelength Near-Infrared MgIn2O4:Ni2+ Phosphor Synthesized via Sol-gel Combustion Method as a Light Source for Night Vision Imaging, Nonvisual Detection, and Anticounterfeiting Display.

Long-wavelength near-infrared (LWNIR) imaging technology has exciting application potential across various fields due to its ability of deeper penetration and unique properties related to its emission wavelength, when compared to short-wavelength near-infrared imaging. However, the limited availability of materials for LWNIR light sources, due to the lack of suitable host materials that constitute luminescence centers, has been a major challenge and technical obstacle in realizing such applications. Here, we developed MgIn2O4:Ni2+ phosphors with an antispinel structure and LWNIR luminescence properties through a sol-gel combustion method. Under excitation at 365 nm, its emission wavelength covers the range of 1000-2000 nm, with a peak emission at approximately 1520 nm, a full width at half-maximum of ∼340 nm, and an optimized photoluminescence quantum yield of ∼21.22%, when an optimal Ni2+ doping content of 1 mol % was used. Studies on the crystal structure of MgIn2O4 have shown that Ni2+ ions preferentially replace the lattice position occupied by Mg2+ ions in the [MgO6] octahedrons, which provides a crystal field microenvironment of weak strength to the Ni2+ luminescence centers and promotes their LWNIR emission with a large Stokes shift. A LWNIR pc-LED device was assembled using the optimized MgIn2O4:Ni2+ phosphor and a near-ultraviolet LED chip (@ 365 nm), and its potential applications, including NIR night vision imaging, nonvisual detection, and anticounterfeiting displays, were demonstrated. Our results show that the antispinel MgIn2O4:Ni2+ phosphor prepared by the sol-gel combustion method is a promising LWNIR luminescence material.

Cyan to orange color tunable emitting of Ca2GdHf2Al3O12: Ce3+, Mn2+ phosphors via energy transfer

Recently, the realization of spectrum-tunable single-phase phosphors has become the focus of phosphor-converted light-emitting diodes (pc-LEDs) research. Herein, a novel color-tunable Ca2GdHf2Al3O12 (CGHAO): Ce3+, Mn2+ single-phase phosphor was prepared. A thorough investigation was conducted into the crystal structure, site occupancy, morphology, luminescent characteristics, energy transfer (ET) process, and thermal quenching. These phosphors show broadband excitation between 200 and 460 nm matching commercially available near-ultraviolet LED chips (380–420 nm). The ratio of dopant ion concentration can be varied to achieve cyan-to-orange chromaticity adjustment due to the Ce3+ → Mn2+ effective ET. By confirming that the ET mechanism is controlled by dipole-quadrupole interaction with 42.64 % efficiency. In particular, under excitation at 405 nm, the optimal sample CGHAO: 5%Ce3+, 15%Mn2+ emits bright yellow light with an IQE of 84.35 %, and has good thermal (Ea = 0.271 eV) and chromatic stability (ΔE = 1.35 × 10−2 at 473K). Based on these findings, color-tunable CGHAO: Ce3+, Mn2+ phosphor could be considered potential candidates for pc-LEDs device applications.

A Nickel-doped, lanthanum gallium germanate-based phosphor as an ultra-broadband short-wavelength infrared region emitter for optical imaging

Short-wavelength infrared region light source (SWIR, λ = 1000–2000 nm) is useful for optical imaging of biological tissues for lack of auto-fluorescence, low intrinsic absorption, and low scattering. Here, we report the synthesis, characterization, and mechanistic studies of a Ni2+-doped, lanthanum gallium germanate-based phosphor, La3Ga5GeO14:Ni2+, that emits SWIR with an ultra-broad bandwidth emission of 1000–2000 nm, a full-width at half maximum (FWHM) of 340 nm, which covers near infrared-II and III regions. The analysis of crystal structure suggests that Ga3+ ions in [GaO6] octahedron lattices are replaced by Ni2+ ions, possibly due to the similar radius shared by both ions. The observed ultra-broadband SWIR luminescence with large Stokes shift is most likely originated from the influence of a strong crystal field on the extent of the cleavage of energy levels of Ni2+ ions, which is supported by the charge density data of [GaO6] octahedra in La3Ga5GeO14 derived from state density functional calculation. A SWIR pc-LED was constructed by packaging the La3Ga5GeO14:Ni2+ phosphor with a near-ultraviolet LED chip, and its potential application in optical imaging of human bodies was explored.

High external quantum yield in near-infrared phosphor Bi2Ga4O9:Cr3+ excited by near-ultraviolet or blue light

The proliferation of portable and intelligent devices featuring Near-Infrared (NIR) light sources as a central component has resulted in a significant need for compact NIR light sources. The technique of NIR phosphor-converted light-emitting diodes (NIR-pc-LEDs) could offer a fresh viewpoint on NIR light sources. The performance of NIR-pc-LEDs is directly influenced by NIR phosphors. However, the development of NIR phosphors with high external quantum yield (EQY) NIR phosphors has been hampered. In this work, we report a mullite-structure NIR phosphor, Bi2Ga4O9: Cr3+ (BGO), which exhibits excellent NIR luminescence properties. The emission spectrum of the optimal doped sample BGO:0.06Cr3+ has two emission peaks at 711 and 763 nm. All samples can be efficiently excited by commercial 365 nm near-ultraviolet LED chips and 450 nm blue LED chips. The internal quantum yield (IQY) reaches an astonishing value of 89.13 % and an EQY of about 65.36 % at 365 nm excitation. Furthermore, BGO:0.06Cr3+ shows a high IQY (∼87.78 %) and EQY (∼41.64 %) upon 450 nm excitation. Moreover, concerning thermal stability, the integrated photoluminescence intensity remains at 82 % and 42 % of that at room temperature when measured at 373 K and 423 K, respectively. The capsuled NIR-pc-LED device can be utilized for blood veins imaging, food safety analysis, and information encryption. These results highlight the promising commercial prospects of BGO:0.06Cr3+ in the fields of bio-imaging and non-destructive testing, among others.

Engineering deep-red Al20B4O36:Cr3+ phosphors for photomorphogenesis

Cr3+ doped phosphors with deep-red luminescence hold great promise as artificial lighting sources for plants growth. Among them, α-Al2O3:Cr3+ is featured with an ultra-intense pure zero phonon line (ZPL) emission with negligible sidebands. Nonetheless, further enhancements in its luminescence thermal stability are required to fully unlock its potential for practical applications. To tackle this challenge, we propose that Al20B4O36 with a negative expansion coefficient could serve as a more favorable host materials for Cr3+ ion, thereby enhancing the luminescence thermal stability. Our first-principles calculations have unveiled similar electronic structures for α-Al2O3:Cr3+ and Al20B4O36:Cr3+, suggesting that the observed zero phonon R-line (2Eg) emission, arising from the 2Eg→4A2g transition in α-Al2O3:Cr3+, might also be present in Al20B4O36:Cr3+. Based on these findings, we prepared Al20B4O36:Cr3+ phosphors using a simple solid reaction method and confirmed that Al20B4O36:Cr3+ indeed exhibits a similar ultra-intense pure ZPL emission centered at 694 nm. Moreover, Al20B4O36:Cr3+ phosphors demonstrate remarkable properties including a high internal quantum efficiency (IQE) of 98.2 % and superior luminescence thermal stability compared to α-Al2O3:Cr3+. A phosphor converted light emitting diode (pc-LED) is developed by coating Al20B4O36:Cr3+ phosphor onto a near-ultraviolet LED chip. The lighting from this deep-red LED significantly impacts the photomorphogenesis of bean sprouts. Our study showcases a rational approach to design novel Cr3+ doped phosphors with enhanced luminescent properties, tailored for specific applications.

Effect of oxygen vacancy on photoluminescence properties of Dy3+ doped K2BaCa(PO4)2 phosphor and remote luminescence multi-layer for white light

Dy3+ ions singly-doped phosphors, emerging as single-component white light-emitting phosphors, have been regarded as a promising candidate for white light generation under ultraviolet (UV) or near-ultraviolet (NUV) excitation. Here, a series of Dy3+ doped K2BaCa(PO4)2 phosphors with single phase was successfully synthesized by solid-state reaction method. Under NUV excitation, K2BaCa(PO4)2: Dy3+ phosphors exhibits the desire blue emission at 490 nm and yellow emission at 580 nm, attributed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively. Interestingly, the broad emission peak centered at 458 nm can also be found and assigned to the oxygen vacancy in K2BaCa(PO4)2 host lattice. Significantly, the emission intensity of the phosphor is greatly enhanced to 4.1 times higher than that of the sample without oxygen vacancy due to the energy transfer from oxygen vacancy to Dy3+ ions. K2BaCa(PO4)2: 0.03Dy3+ phosphor with high quantum yield of 76.9% exhibits good thermal stability with the relative emission intensity of 95.7% and 88.6% at 323 K and 373 K, respectively. Subsequently, the white light with correlated color temperature (CCT) of 4521 K and color rendering index (CRI) of 79 can be achieved for the optimized K2BaCa(PO4)2: 0.03Dy3+ phosphor packaged with NUV LED chip (365 nm). Further, the remote luminescence multi-layer based on K2BaCa(PO4)2: 0.03Dy3+ phosphors is fabricated on glass substrate by screen printing technology and exhibit better heat dissipation performance than that of the conventional NUV LEDs, which can be a promising candidate of single-component phosphors for the manufacture of white LEDs with adjustable remote luminescent layers.

Luminescent properties and energy transfer mechanism from Tb3+ to Eu3+ in single-phase color-adjustable Sr3MgSi2O8:Eu3+,Tb3+ phosphor prepared by the sol-gel method

A series of single-phase color-adjustable Sr3MgSi2O8:Eu3+,2Tb3+ phosphors were synthesized with the application of sol-gel method. The crystal structure, luminescence characteristics, fluorescence lifetime, energy transfer mechanism and thermal stability of phosphors were investigated. The results show that the emission spectrum of Sr3−x−yMgSi2O8:xEu3+,yTb3+ compose both the 5D4→7F5 transition of Tb3+ and the 5D0→7F1, 5D0→7F2 transition of Eu3+ at the excitation wavelength of 238 nm. The optimal doping concentration of Tb3+ was determined to be 2% when concentration quenching effect was comprehensively considered. On the basis of the energy transfer of Tb3+→Eu3+, the emission peak intensity of Eu3+ increases and that of Tb3+ decreases with the rising Eu3+ concentration. The unidirectional energy transfer efficiency of Tb3+→Eu3+ reaches 89.4% when the Eu3+ doping concentration is 8%. On the basis of Dexter's theory, the major mechanism of energy transfer lies in the electric dipoles interaction between Tb3+ and Eu3+. With an activation energy of 0.309 eV, Sr2.95MgSi2O8:3%Eu3+,2%Tb3+ phosphors enjoys good thermal stability. Its color coordinate diagram indicates that the luminous colors of phosphors can be customized from red to orange, then to green with the changing doping concentrations of Eu3+ and Tb3+. Based on Sr3MgSi2O8:Eu3+,Tb3+ phosphors has a good matchability with ultraviolet and near-ultraviolet LED chips, so it can be considered that Sr3MgSi2O8:Eu3+,Tb3+ phosphors have good application potential in the field of ultraviolet and near-ultraviolet white light emitting diodes.

Turning on the luminescence of Sr5(PO4)3Cl: Eu2+ by doping of La, Gd and Lu ions for full-spectrum lighting application

Blue phosphor Sr5−x-yRy(PO4)3Cl:xEu2+ (R = La, Gd, Lu) was prepared via solid-state reaction process, in which R3+ replaces part of Sr2+ ions in the matrix to benefit Eu2+ luminescence. The change of Eu2+/Eu3+ values were studied by XPS, and the results shown that the incorporation of R3+ in the matrix resulted in the values increase of Eu2+/Eu3+. And substitute R3+ non-equivalently for Sr2+, the modified Sr5−x-yRy(PO4)3Cl:xEu2+ phosphors show better luminescence intensity and thermal stability. The emission intensity of Sr4.72Lu0.2(PO4)3Cl:0.08Eu2+ is 1.97 times of Sr4.95(PO4)3Cl:0.05Eu2+. Moreover, the thermal quenching of Eu2+ photoluminescence could be reduced. Compared to the commercial BAM:Eu2+ phosphor, the stabilities of all Sr4.72R0.2(PO4)3Cl:0.08Eu2+(R=La3+, Gd3+ and Lu3+) phosphors are better than that of BAM:Eu2+ at the temperatures below 100 °C. The luminescent intensity of Sr4.72Lu0.2(PO4)3Cl:0.08Eu2+ maintains 95% while BAM:Eu2+ is only 88% of the initial intensity at 150 °C. By combining Sr4.72Lu0.2(PO4)3Cl:0.08Eu2+, Y3(Al,Ga)5O12:Ce3+ and CaAlSiN3:Eu2+ with 400 nm near-ultraviolet LED chip, a white-light-emitting diode was obtained. The fabricated WLED device with CIE color coordinates x = 0.3896, y = 0.3788, low CCT (3775 K) and high Ra (95.1), has enormous potential application in full-spectrum lighting field.

Site occupancy and tunable photoluminescence properties of Eu2+-Activated Ba3Sc(BO3)3 phosphors for white light emitting diodes

A series of emission-tunable Ba3-xSc(BO3)3: xEu2+ (0 ≤ x ≤ 0.15) and Ba2.97-yGdySc1-yMgy(BO3)3: 0.03Eu2+ (0 ≤ y ≤ 0.15) phosphors were synthesized by a solid-state method. Structure analysis of X-ray powder diffraction (XRD) and Rietveld refinement show that Eu2+ ions occupy randomly at Ba sites of hexagonal lattice with space group P63cm. Photoluminescence emission spectra and the decay curves of phosphors demonstrated the existence of multiple Eu2+ emitting centers. Eu2+ ions occupy at four Ba sites of Ba3-xSc(BO3)3: xEu2+ (0.03 ≤ x ≤ 0.15) emit orange light (λem = 670 nm and 560 nm) through 370 nm UV excitation. The broader absorption band, ranging from 220 nm to 550 nm, matches well with the near-ultraviolet LED chips. Furthermore, color tuning from orange to red is successfully achieve by the double doping of Gd3+-Ba2+ and Mg2+-Sc3+ in Ba2.97Sc(BO3)3: 0.03Eu2+. Our results indicate that red emission Ba3Sc(BO3)3: Eu2+ phosphors is an ideal candidate for the application in white light-emitting diodes.

Spectral Re-Absorption Effect of Multi-Primary Phosphor Thin Films and Various Package Structures on the Performance of Near-Ultraviolet White LED

We prepared blue, green and red phosphor thin films (PTFs) with different phosphor concentrations used for near-ultraviolet (NUV) LEDs respectively, and then investigated their spectral re-absorption/excitation/emission process. The functional relationship between optical powers and concentrations were established by using the exponential equation. The relationship between the spectral deformations and concentrations were evaluated by the correlation coefficient. Based on NUV LED chip, eight package structures of white LEDs were prepared. The luminous efficiency (LE) of white LED based on Blue/Green/Red@NUV laminate structure reached 85.48 lm/W, which was 27.7% higher than that of hybrid structure, correlated color temperature (CCT) was 3518K, Rf was 83, Rg was 106, and when hybrid structure thickness was reduced to one-third points, the LE increased by 21.5% to 81.36 lm/W, CCT was 4200K, Rf was 93, Rg was 101, CCT uniformity test showed that the uniformities of laminated and hybrid structures were 80.06% and 96.91% respectively. The results showed that the laminated structure was beneficial to improve the LE, while the hybrid structure had the advantage of uniformity improvement and spectrum continuity due to multi-particle scattering and spectral deformation of the phosphor.

Synthesis and photoluminescent properties of orange-emitting Sm3+-activated KPb4(PO4)3 phosphor for LEDs

A series of Sm3+-doped KPb4(PO4)3 phosphors have been successfully synthesized by high-temperature solid-state reaction method, and the structure, morphology and luminescent properties were investigated. The SEM images suggest that the prepared phosphor has an irregular morphology with a diameter of about 10 ~ 20 μm. Under near-ultraviolet (NUV) light (404 nm) excitation, all prepared phosphors KPb4-xSmxP3O12 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.15, 0.2, 0.3, 0.4 and 0.5) show the characteristic f → f emission bands of the Sm3+ activator. And the emission intensities have an upward trend with increasing the Sm3+ concentration when x is lower than 0.1. By monitoring 598 nm emission, the excitation spectrum of KPb3.9Sm0.1(PO4)3 contains a series of sharp bands in the range of 250 ~ 500 nm, which matches well with the NUV LED chip. The CIE coordinates of KPb3.9Sm0.1(PO4)3 phosphor was evaluated to be (0.5714, 0.4253), corresponding to orange color with a high color purity of about 90%.

Ce3+/Mn2+-activated Ca7(PO4)2(SiO4)2: efficient luminescent materials for multifunctional applications.

To develop new efficient phosphors for LEDs based on multifunctional applications, a series of Ce3+/Mn2+ activated Ca7(PO4)2(SiO4)2 (CPS) samples were prepared by solid-state reaction method. Upon 365 nm excitation, a broad emission band around 439 nm in the Ce3+-single-doped CPS was observed. The optimal Ce3+ concentration was determined to be 3%, for which the quantum efficiency was obtained to be 90.4%, higher than that of the commercial BAM phosphor. By monitoring 458 nm, an intense and broad excitation band was found from 240 to 400 nm, which can match well with the near-ultraviolet (NUV) LED chip. For Ce3+-Mn2+ codoped CPS, a new red emission band belonging to Mn2+ appeared and an energy transfer from Ce3+ to Mn2+ was confirmed. It was also found that the emission spectra of Ce3+/Mn2+ could well cover the optical absorption bands of plants. The fabrication of the phosphors on NUV LED chip indicates that the present phosphors could be promising in solid lighting and plants growth.

(BaSr)2SiO4:Eu2+ nanorods with enhanced luminescence properties as green-emitting phosphors for white LED applications

To meet the requirements of warm white light-emitting diodes (WLEDs) with extreme thermal stability, high color rendering index and low color temperature, which is equivalent to natural sunlight, we need to develop novel phosphor materials that can efficiently absorb excitation energy from near-ultraviolet (NUV) LEDs and produce desired visible emissions. The Sr2+ and Eu2+ ions co-activated Ba2SiO4 ((BaSr)Si:Eu2+) green-emitting nanophopshors for NUV or blue excitation-based WLEDs are reported. After annealing at 1300 °C, the X-ray diffraction patterns established the pure orthorhombic phase of (BaSr)Si:Eu2+ nanophosphors. The evolution of (BaSr)Si:Eu2+ nanorods from the surface of the sub-micron sized (BaSr)Si:Eu2+ particles showed a tremendous effect on the luminescent properties by enhancing the transmittance of the (BaSr)Si:Eu2+ nanophosphor. The incorporation of Sr2+ ions along with Eu2+ ions into the Ba2+ sites, the emission intensity was increased, and also the quantum efficiency was enhanced from 47 to 59%. Upon excitation at 370 nm, the Ba2SiO4:Eu2+ phosphor exhibited a bluish-green emission while the yellowish-green emission was revealed by the (BaSr)Si:Eu2+ nanophosphor. The thermal stability of the (BaSr)Si:Eu2+ nanophosphor was verified at elevated temperatures and the activation energy for thermal quenching was found to be 0.38 eV. When the (BaSr)Si:Eu2+ nanophosphor was coated on a NUV LED chip, the enriched green emission was observed by increasing the input current from 100 to 250 mA. The (BaSr)Si:Eu2+ is expected to be a promising green-emitting phosphor material for the fabrication of NUV or blue excitation-based warm WLEDs for general illumination.

White Light-Emitting Diodes With High Color Rendering Index and Tunable Color Temperature Fabricated Using Separated Phosphor Layer Structure

In this letter, phosphor-converted white light-emitting diodes (pc-WLEDs) were fabricated using two separated phosphor layers (B&G up/R down) that combine three color phosphors (blue, green, and red) with near-ultraviolet LED chips. The pc-WLEDs have a high color rendering index (CRI) and a tunable color temperature. Regarding the spectra of the phosphors, the CRI value increased with the increasing percentage of overlapping area between the spectra deconvoluted from the electroluminescence spectrum of the pc-WLED. By controlling the thickness of the phosphor layers, the pc-WLEDs with high CRI values and various color temperatures can be obtained. The correlated color temperature and the CRI value of the optimized pc-WLED were 4606 K and 93.8, respectively.

Luminescence of emission-tunable Na15.6Ca3.84Si12O36:Ce3+,Tb3+,Na+ phosphors for near-ultraviolet light-emitting diodes

A series of Na15.6Ca3.84Si12O36:Ce3+,Tb3+,Na+ (NCS:Ce3+,Tb3+,Na+) phosphors were prepared by conventional solid-state reaction method, and their photoluminescence properties under near-ultraviolet (NUV) excitation were studied. The excitation spectrum of Ce3+-single-doped NCS showed a broad excitation band from 250 to 400 nm, which could well match with the emission wavelength of the NUV LED chip. Upon 365 nm excitation, the NCS:Ce3+,Na+ phosphor demonstrated a blue emission in the range of 400–600 nm with the predominated peak at 443 nm. By co-doping Tb3+ into NCS:0.04Ce3+,0.04Na+, tunable-emission was realized due to the energy transfer from Ce3+ to Tb3+, and nearly white light was also obtained. The investigation also revealed that warm white light could be further generated by combining the NCS:0.04Ce3+,yTb3+,(0.04+y)Na+ with other red-emitting phosphors. Thus, the NCS:Ce3+,Tb3+,Na+ phosphors could be promising candidate for white LEDs.

Investigations on photoluminescence and cathodoluminescence properties of Ca3La6(SiO4)6:Tb3 +, Mn2 +

Tb3+/Mn2+ activated Ca3La6(SiO4)6 (CLS) phosphors were prepared by solid-state reaction method, and their photoluminescence and cathodoluminescence (CL) properties were investigated. The CLS:Tb3+ sample shows a yellowish green emission under 377nm excitation, and the excitation spectrum reveals the excitation peaks between 340 and 390nm can match with the near-ultraviolet LED chip. Excellent thermal stability has been obtained in the CLS:Tb3+ phosphor by studying the temperature dependence of the Tb3+ emission intensity. By introducing Mn2+ into CLS:Tb3+, tunable emissions are generated due to the efficient energy transfer from Tb3+ to Mn2+. The CL spectrum of CLS:Tb3+ displays that the characteristic 5D4-7FJ (J=6−3) transitions of Tb3+ are found under electron beam excitation. The above investigation results imply that the CLS:Tb3+, Mn2+ phosphors could have potential applications on LEDs and FEDs.

Investigations on the luminescence properties of Na0.34Ca0.66Al1.66Si2.34O8:Eu2+/Eu3+/Sm3+ phosphors

Na0.34Ca0.66Al1.66Si2.34O8:Eu2+/Eu3+/Sm3+ (NCAS:Eu2+/Eu3+/Sm3+) phosphors were prepared by solid-state reaction method, and their photoluminescence properties were investigated. The optical bandgap of the NCAS compound was determined to be 4.04 eV experimentally. The excitation spectrum of NCAS:2%Eu2+ shows a broad excitation band from 240 to 410 nm, which could match with the near-ultraviolet LED chip. Upon 365 nm excitation, blue emissions between 375 and 650 nm have been obtained, accompanied with a continuous red-shift for the predominated emission peaks with increasing Eu2+ concentration. Red and red–orange emissions are gained in the Eu3+/Sm3+ activated NCAS phosphors, respectively. And the spectra features reveal the Eu3+ and Sm3+ ions occupy asymmetry sites. The above investigation results indicate the NCAS:Eu2+/Eu3+/Sm3+ phosphors could have promising applications in white LEDs.

Photoluminescence properties of CaBi2Ta2O9:RE3+ (RE=Sm, Tb, and Tm) phosphors

Sm3+, Tb3+, and Tm3+ doped CaBi2Ta2O9 (CBTO) with the layered perovskite structure were synthesized by the solid-state reaction method. The photoluminescence properties, structure, morphology and color coordinates of the phosphors were explored in detail. CBTO:RE3+ (RE=Sm, Tb, and Tm) can emit light of three colors, reddish orange, green and blue. Under near ultraviolet (NUV) excitation, CBTO:Sm3+ show an intense reddish orange emission transition of 4G5/2→6H7/2 at 602nm, the novel green emission of CBTO:Tb3+ and blue emission of CBTO:Tm3+ peak at 544 and 458nm. The study provides a comprehensive understanding of the variation in the luminescent properties of CBTO with doping concentration, and the mechanism of concentration quenching in CBTO:Sm3+ phosphors is revealed, and the critical distance of CBTO:Sm3+ is calculated to be 2.72nm. CBTO:RE3+ (RE=Sm, Tb, and Tm) with NUV LED chip can realize white light.

Phase transition and multicolor luminescence of Eu2+/Mn2+-activated Ca3(PO4)2 phosphors

Intense blue-green-emitting Eu2+: Ca3(PO4)2 and tunable multicolor-emitting Eu2+/Mn2+: Ca3(PO4)2 phosphors are prepared via a solid-state reaction route. Eu2+-doped orthorhombic Ca3(PO4)2 phosphor exhibits a broad emission band in the wavelength range of 400–700nm with a maximum quantum yield of 56.7%, and the emission peak red-shifts gradually from 479 to 520nm with increase of Eu2+ doping content. Broad excitation spectrum (250–420nm) of Eu2+: Ca3(PO4)2 matches well with the near-ultraviolet LED chip, indicating its potential applications as tri-color phosphors in white LEDs. Interestingly, Mn2+ co-doping into Eu2+: Ca3(PO4)2 leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi-color luminescence from green to red via Eu2+→Mn2+ energy transfer, under 365nm UV lamp excitation.

Luminous characteristics and thermal stability of BaMgAl 10O 17:Eu 2+ phosphor for white light-emitting diodes

A blue-emitting phosphor, BaMgAl 10O 17:Eu 2+ (BAM) was prepared by the solid-state reaction and X-ray powder diffraction (XRD) analysis confirmed the formation of BAM. Photoluminescence (PL) results showed that the phosphor can be efficiently excited by the light from near ultraviolet (NUV) to visible, and exhibited bright blue emission. The effect of the doped-Eu 2+ in BAM on the PL was investigated. To improve the BAM's thermal stability, BAM doped with additional Mg 2+ was studied. The experiment results showed that additional 0.05 mol Mg 2+-doped BAM had the highest emission intensity and thermal stability. By combining with NUV LED chip (GaN-based 380 nm emitting), a novel intense white LED was fabricated based on the blue phosphor BAM and a red phosphor Ca(La 0.5Eu 0.5) 4Si 3O 13. The white LED has the characteristics of color-rendering index of 87, CIE chromaticity coordinates ( x, y) of (0.3225, 0.3187), color temperature Tc of 5680 K, and light output of 51.7 lm/W under the forward-bias current of 20 mA. As the current increases, the relative intensity increases, the correlated color temperature Tc increases from 4000 to 7900 K and the color-rendering index Ra increases from 83 to 91 simultaneously.