UV LED Chip Research Articles

A novel tunable blue-green-emitting CaGdGaAl2O7:Ce(3+),Tb(3+) phosphor via energy transfer for UV-excited white LEDs.

CaGdGaAl2O7 and CaGdGaAl2O7:Ce(3+),Tb(3+) have been synthesized by a traditional solid state reaction for the first time. The Rietveld refinement confirmed that CaGdGaAl2O7 has a tetragonal crystal system with the space group P4[combining macron]21m. The photoluminescence properties show that the obtained phosphors can be efficiently excited in the range from 330 to 400 nm, which matches perfectly with commercial UV LED chips. A tunable blue-green emitting CaGdGaAl2O7:Ce(3+),Tb(3+) phosphor has been obtained, by codoping Ce(3+) and Tb(3+) ions into the host and varying their relative ratios, and may be a good candidate for blue-green components in UV white LEDs. The luminescence properties and lifetimes reveal an efficient energy transfer from the Ce(3+) to Tb(3+) ions. The energy transfer is demonstrated to be a dipole-quadrupole mechanism, and the critical distance for Ce(3+) to Tb(3+) calculated by the concentration quenching is 12.25 Å.

White light emission of Eu3+/Ag co-doped Y2Si2O7

The Eu3+/Ag co-doped rare earth disilicate Y2Si2O7 microcrystal was synthesized by sol-gel method. Through controlling the thermal treatment process of Y2Si2O7:Eu3+/Ag precursor, various phases (amorphous, α, β, γ, δ) were prepared. White light emission was observed under UV light excitation in the samples heavily doped with Ag. The white light was realized by combining the intense red emission of Eu3+, the green emission attributed to the very small molecule-like, non-plasmonic Ag particles (ML-Ag-particles), and the blue emission due to Ag ions. Results demonstrated that Eu3+/Ag co-doped Y2Si2O7 microcrystal could be potentially applied as white light emission phosphors for UV LED chips.

Luminescence properties of a novel CaLa4Si3O13:Sm3+ phosphor for white light emitting diodes

A new series phosphors of Sm3+ ions activated CaLa4Si3O13 (CLSO) were synthesized by solid state reaction. The crystal structure and photoluminescence properties of CLSO:Sm3+ phosphors were investigated. The excitation and emission spectra indicated that the CLSO:Sm3+ phosphors could be excited by near UV or blue LED chip effectively, giving a strong orange–red emission centered at 602nm which corresponded to 4G5/2→6H7/2 transition of Sm3+ ions under the excitation of 404nm. The results suggested that the CLSO:0.015Sm3+ phosphor was the brightest orange–red emission with CIE coordinates (x=0.59, y=0.41). CaLa4Si3O13:Sm3+ was a promising orange–red emitting phosphor for white LED applications.

A double substitution of Mg2+-Si4+/Ge4+ for Al(1)(3+)-Al(2)3+ in Ce3+-doped garnet phosphor for white LEDs.

The influence of Mg(2+)-Si(4+)/Ge(4+) incorporation into Ce(3+)-doped Y3Al5O12 garnet phosphors on the crystal structure and luminescence properties is described in this work. X-ray diffraction with Rietveld refinements, photoluminescence spectra, absolute quantum yield, thermal quenching behavior, and lifetimes were utilized to characterize samples. The introduction of Mg(2+)-Si(4+)/Ge(4+) leads to an obvious red shift of emission wavelength under the excitation of blue light, especially for the series of Mg(2+)-Si(4+) substitutions, which is suited for white light-emitting diodes (LEDs) with low color temperatures and good color rendering using only a single phosphor. More interestingly, an additional emission band locating at high-energy was observed with ultraviolet excitation, which is different than previous literature. Under the excitation of ultraviolet, the emission color for the Mg(2+)-Si(4+) substitutions can be tuned from yellow-green to blue, which is expected to obtain single-phased phosphors with white emission excited with UV-LED chip. The usual Ce(3+) emission band at low energy has stronger quenching at high temperatures. The mechanisms for the observed phenomena are discussed.

Luminescence investigations of Sr3SiO5:Eu2+ orange–yellow phosphor for UV-based white LED

An orange–yellow phosphor, Sr3SiO5:Eu2+, was synthesized by a high energy ball milling method. Sr3SiO5:Eu2+ exhibits an orange–yellow emission under the blue radiation excitation. The excitation, emission spectra and lifetime decay curves of 4f65d1→4f7 of Eu2+ were measured and interpreted with respect to their crystal structures and multi-site occupations of divalent europium in the hosts. The blue emission disappears and the orange–yellow emission reaches the peak value when Eu2+ doping content is 0.003mol. Namely, the energy transfer takes place between the Eu2+ activators, which is located at two different crystallographic sites in the Sr3SiO5. And the energy transfer mechanism is the dipole–dipole interaction. The results show that the Eu2+ doped powder phosphors containing Sr3SiO5 powder can be used as potential matrix materials for a high power white LED pumped by the UVLED chip.

Luminescence properties of Eu-activated alkaline and alkaline-earth silicate Na2Ca3Si6O16

Yellow-emitting phosphors of Na2Ca3Si6O16:Eu2+ was prepared by wet chemistry sol–gel method. X-ray powder diffraction and SEM measurements were applied to characterize the structure and morphology, respectively. The luminescence properties were investigated by the photoluminescence excitation and emission spectra, decay curve (lifetimes), CIE coordinates and the internal quantum efficiencies. The excitation spectra can match well with the emission light of near UV-LED chips (360–400nm). Na2Ca3Si6O16:Eu2+ presents a symmetric emission band from 4f65d1⟶4f7(8S7/2) transitions of Eu2+ ions on doping below 3.0mol%. On increasing Eu-doping levels, the sample contains two kinds of emission centers, i.e., Eu2+ and Eu3+ ions, which present the characteristic broad band (5d⟶4f) and narrower (4f⟶4f) luminescence lines, respectively. The energy transfer, the luminescence thermal stability (activation energy ΔE for thermal quenching) and luminescence mechanism of Na2Ca3Si6O16:Eu2+ phosphors were discussed by analyzing the relationship between the luminescence characteristics and the crystal structure.

Eu2+ & Mn2+ co-activated Sr3Si6O3N8 green emitting phosphors with enhanced fluorescence emission

Mn2+/Eu2+ co-activated Sr3Si6O3N8 phosphor was synthesized by conventional solid state reaction. Sr3Si6O3N8:Eu2+, Mn2+ green-emitting phosphor could be effectively excited by UV–visible light from 300nm to 500nm, which matched well with the emission of UV and blue LED chips. The luminescence intensity of Sr3Si6O3N8:Eu2+ could be efficiently enhanced by co-doping with Mn2+ ions. The energy transfer mechanism between Eu2+ and Mn2+ in Sr3Si6O3N8:Eu2+, Mn2+ phosphors is dominated by electric multipole effect interaction.

Structure and photoluminescence properties of Na2Y2B2O7:Ce3+,Tb3+ phosphors for solid-state lighting application

Novel phosphors of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce3+ emission properties and the crystal structure of Na2Y2B2O7 is built and the result shows that Ce3+ ions occupy two non-equivalent Y3+ sites in the host. The codoping of Tb3+ in Na2Y2B2O7:Ce3+ can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce3+→Tb3+. The energy transfer processes of Ce3+–Ce3+ and Ce3+–Tb3+ are analysed and determined to be electric dipole–dipole and dipole–quadrupole, respectively. The broad PLE spectra of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs.

Characterization of HVPE‐grown UV LED heterostructures

AbstractIn this paper, we report on growth of ultraviolet light‐emitting diode (UV LED) heterostructures by hydride vapour phase epitaxy (HVPE) on sapphire substrates and results of the heterostructures characterization by X‐ray diffractometry, scanning electron microscopy, photo‐ and electroluminescence, micro‐photoluminescence, collected from the cleaved edges and the surface of the heterostructure with lateral resolution of about 1 µm. The heterostructures demonstrate efficient hole injection and low droop of the external quantum efficiency. Packaged 360 nm UV LED chips have wall‐plug efficiency of 1‐1.5%. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and luminescent properties of high brightness MRE(MoO4)2:Eu3+ (M = Li, Na, K; RE = Gd, Y, Lu) red phosphors for white LEDs

A series of Eu3+-activated double molybdate phosphors MRE(MoO4)2 (M = Li, Na, K; RE = Gd, Y, Lu) have been successfully prepared via the conventional solid-state reaction method. The effects of alkali cations and rare earth ions on the luminescence of MRE(MoO4)2:Eu3+ were investigated in detail. The experimental results show that the emission intensity was found to decrease with increasing the size of alkali cations or decreasing the size of rare earth ions. Under 393 nm light excitation, all compounds exhibited strong red emission at about 613 nm due to 5D0 → 7F2 transition of Eu3+. Compared with the commercially available red phosphor Y2O3:Eu3+, the emission intensity of the obtained phosphors is much stronger than that of Y2O3:Eu3+. Additionally, the excitation spectra of these phosphors implied that the MRE(MoO4)2:Eu3+ phosphors can absorb not only the emission of near UV-LED chips but also that of blue LED chips. The CIE chromaticity coordinates are close to the National Television Standard Committee (NTSC) standard CIE chromaticity coordinate values for red (0.67, 0.33). All the results indicate that these phosphors are promising red-emitting phosphors pumped by near-UV or blue light.

Luminescence Performance and Structural Characteristic of Eu2+-Activated Na2BaSi2O6 Phosphor

Green-emitting phosphor of Eu2+-doped sodium barium silicate Na2BaSi2O6 was prepared by chemical sol-gel method. The X-ray powder diffraction, SEM, photoluminescence pectra and time resolved emission spectra were measured. The excitation spectra can well match with the emission light of near UV-LED chips (360–400 nm). The luminescence was suggested to originate from two kinds of Eu2+ centers, which occupy both Ba2+ and Na(2) sites in Na2BaSi2O6 lattices. Energy transfer among the Eu2+-centers was discussed by analyzing the photoluminescence spectra, concentration-dependent luminescence intensity and decay lifetimes. The dependence of the luminescence intensity of Na2BaSi2O6:Eu2+ on temperatures was measured. The activation energy (ΔE) for thermal quenching was reported. The luminescence properties of Na2BaSi2O6:Eu2+ were compared with that of BaSiO3:Eu2+. The high luminescence of Na2BaSi2O6:Eu2+ were discussed on the base of luminescence properties and microstructure of Eu2+ ion.

Structure, photoluminescent and cathodoluminescent properties of a rare-earth free red emitting β-Zn3B2O6:Mn2+phosphor

A rare-earth free red emitting β-Zn3B2O6:Mn(2+) phosphor was prepared by a solid-state reaction method. The crystal structure, photoluminescent and cathodoluminescent properties of β-Zn3B2O6:Mn(2+) were systematically investigated. The absorption and photoluminescence excitation spectra confirm that β-Zn3B2O6:Mn(2+) matches the UV LED chip. Under UV light and low-voltage electron beam excitations, an interesting orange-red emission band centered at ∼600 nm of Mn(2+) at the tetrahedral Zn(2+) sites is observed. Besides, the unusual red shift with increasing Mn(2+) content is also found and contributed to an exchange interaction between Mn(2+). In addition, under low-voltage excitation, β-Zn3B2O6:Mn(2+) exhibits higher color purity of 98.1% than that of the commercial ZnS:Ag,Cd yellow phosphor and reported ZnGeN2:Mn(2+) orange phosphor, which indicated the β-Zn3B2O6:Mn(2+) has a patenting application in FEDs.

Synthesis and Luminescent Properties of Red Phosphor BaY2O4: Eu3+ for White Light-Emitting Diodes

The rare-earth Eu3+doped BaY2O4red phosphor synthesized by citric acid sol-gel method. The structure, morphology and composition of the red phosphor were characterized by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. The results show that the distribution of the pure phase BaY2O4: Eu3+particles after annealing at 800 °C was irregular, small size of particle is 0.2 μm to 0.4 μm. The excitation spectra of synthesized phosphor at 610 nm monitoring were composed of a broadband and a series of sharp peaks, the strongest excitation peak at 466 nm, the secondly at 395nm. It was indicated that BaY2O4: Eu3+phosphor matching with the widespread applied the output wavelengths of UV LED and blue LED chips. The main emission spectra of samples under blue light excitation is Eu3+ions5D07F2electric dipole transition with a strong red light, so that the BaY2O: Eu3+phosphor may be a better candidate for red component for white LED.

Novel yellowish-green emitting luminescence in Ca7Si2P2O16:Eu2+ phosphor

Color tunable green-origin-emitting phosphor of Eu2+-doped phosphate-silicate Ca7Si2P2O16 was prepared by chemical sol–gel method. The X-ray powder diffraction, the photoluminescence excitation and emission spectra, time resolved spectra, and thermal stability were measured. The excitation spectra can well match with the emission light of near UV-LED chips (360–400nm). The tunable luminescence was realized by changing Eu2+-doping concentration. Ca7Si2P2O16:Eu2+ displays two typical luminescence centers, which were suggested to originate from two Ca2+ sites in the host. With increasing Eu2+ doping concentrations, the green emission band shifts to long wavelength. Energy transfer between the two different Eu2+ ions is discussed by analyzing the photoluminescence excitation and emission spectra, concentration-dependent luminescence intensity, and lifetimes. The dependence of the luminescence intensity of Ca7Si2P2O16:Eu2+ on temperatures was measured. The activation energy (ΔE) for thermal quenching was reported.

Facile plasma-induced fabrication of fluorescent carbon dots toward high-performance white LEDs

In this study, we report a facile plasma-induced method to fabricate photoluminescent carbon dots (CDs) using acrylamide as the precursor in few minutes. The Fourier transform infrared spectra, UV–Vis absorption spectra, photoluminescence, fluorescent lifetime, and transmission electron microscopy of the as-prepared CDs were investigated thoroughly. The CDs have a narrow size distribution of 3–4 nm and exhibit strong blue fluorescence with quantum yield of ~6 %. More importantly, we explored the CDs as color converters along with CdTe quantum dots to generate white light-emitting diodes (LEDs) using a UV-LED chip as the excitation light source. Compared with the conventional YAG:Ce phosphor-based white LEDs, this resulted LED emitted white light with a higher color rendering index up to 87, which may find their potential in optoelectronic device.

Synthesis and luminescent properties of high brightness MLa(WO4)2:Eu3+ (M=Li, Na, K) and NaRE(WO4)2:Eu3+ (RE=Gd, Y, Lu) red phosphors

Eu3+-activated double tungstates phosphors MLa(WO4)2 (M=Li, Na, K) and NaRE(WO4)2 (RE=Gd, Y, Lu) have been successfully prepared via the conventional solid-state reaction method. The effects of alkali ions and rare earth ions on the luminescence of MLa(WO4)2:Eu3+ and NaRE(WO4)2:Eu3+ were investigated. In MLa(WO4)2:Eu3+ system the emission intensity was found to decrease with increasing the size of alkali ions, and in NaRE(WO4)2:Eu3+ system the emission intensity can be ordered as follows: Lu>Y>Gd. Moreover, under 393nm light excitation all compounds exhibited strong luminescence of 5D0→7F2 at 615nm. The excitation spectra implied that these phosphors can absorb not only the emission of near UV-LED chips but also that of blue LED chips. All the results indicate that these phosphors are promising red-emitting phosphors pumped by near-UV or blue light.

Low-temperature combustion synthesis and luminescent properties of SrMgAl10O17：Eu2+, Er3+ high brightness blue phosphors

The SrMgAl10O17:Eu2+ and SrMgAl10O17:Eu2+, Er3+ blue phosphors were synthesized by the combustion synthesis method. Their crystal structures and luminescent properties were analyzed by X-ray diffraction (XRD)、scanning electron microscope (SEM) and photoluminescence spectra, respectively. The XRD and SEM results indicate that the sample is well-crystallized in the combustion procedure, and its crystal structure has not changed when doped with low concentrations of rare-earth ions. PL results show that the phosphor of SrMgAl10O17:Eu2+ can be effectively excited by near UV LED chip with a broad emission spectrum extending from 430 nm to 520 nm, and has main peaks located at 460nm. Furthermore, the sample of the luminous intensity is the largest when the Er2+, Er3+ co-doped concentration is 4%, and the emission intensity of Sr0.95MgAl10O17:0.05Eu2+, Er3+ phosphor is significantly enhanced 54.9% higher than that of SrMgAl10O17:Eu2+ phosphor. It is indicated that Er3+has good sensitization effect for Eu2+ in luminescence, and this can be explained by the theory of energy transfer.

Tunable white luminescence and energy transfer in novel Cu^+, Sm^3+ co-doped borosilicate glasses for W-LEDs

The luminescent properties of novel Cu⁺, Sm³⁺ single- and co-doped borosilicate glasses were systematically investigated by absorption, excitation, emission spectra and decay curves. Cu⁺ single-doped glasses emit broad luminescence band covering all the visible range. And their peaks shift to blue with decreasing excitation wavelength from 330 to 280 nm. Cu⁺, Sm³⁺ co-doped samples generate the varied hues from blue white to pure white and eventually to yellow white due to an efficient energy transfer from Cu⁺ to Sm³⁺. Our research indicates the potential application of Cu⁺, Sm³⁺ co-doped borosilicate glasses as converting phosphors for white LEDs pumped by UV LED chips.

Enhanced luminescence of Sr3Si6O3N8:Eu2+ phosphors by co-doping with Ce3+

Eu2+/Ce3+ co-activated Sr3Si6O3N8 phosphor was synthesized by conventional solid-state reaction. Sr3Si6O3N8:Eu2+, Ce3+ green-emitting phosphor could be effectively excited by UV–vis light from 395 to 450nm, which matched well with the emission of UV LED chips. The luminescence intensity of Sr3Si6O3N8:Eu2+ could be efficiently enhanced by co-doping with Ce3+. The energy transfer (ET) mechanism from Ce3+ to Eu2+ in Sr3Si6O3N8:Ce3+, Eu2+ phosphors is dominated by electric dipole–dipole interaction, and the critical distance is calculated to be about 25.44Å by theory of energy transfer.

Sb^3+/Mn^2+ co-doped tunable white emitting borosilicate glasses for LEDs

Luminescent properties of Sb(3+)/Mn(2+) co-doped borosilicate glasses containing no rare earth ions were systematically investigated through absorption, excitation, emission spectra, and decay curves. Upon 250-340 nm light excitation, the glasses exhibit broad blue emission at 400 nm (Sb(3+)) and red emission at 615 nm (Mn(2+)). The varied emitted color from blue through white and eventually to red can be obtained by properly tuning the content of Mn(2+) ions due to energy transfer from Sb(3+) to Mn(2+). Our investigation shows that Sb(3+)/Mn(2+) co-doped glasses may provide a new platform to design and fabricate luminescent materials for UV LED chips in the future.