Near-ultraviolet Chip Research Articles

Molybdenum substitution induced luminescence enhancement in Gd2W1-xMoxO6:Eu3+ phosphors for near ultraviolet based solid-state lighting

A series of the Eu3+-activated Gd2W1-xMoxO6 phosphors were synthesized by a high-temperature solid-state reaction method. The phase composition, ultraviolet-visible diffuse reflectance spectra, photoluminescence and decay properties of the phosphors were investigated. Through adjusting the Mo6+ ion concentration, the excitation band of the studied sample was gradually shifted to longer wavelength. Under 376 nm excitation, the strong red emission at 610 nm and weak yellow emission centered at 591 nm were detected, indicating that Eu3+ occupies non-inversion symmetry sites in the host lattices. With elevating the dopant concentration, the emission intensity of synthesized products was greatly enhanced and achieved its optimum value when x = 0.95 which was 2.33 times higher than that of the Gd2WO6:Eu3+ compounds. The quantum efficiency of resultant samples was as high as 76.1%. Moreover, the Judd-Oflet theory was used to study the local structure environment behaviors of the Eu3+ ions in the host lattices. Finally, a red LED device, which consisted of a near-ultraviolet chip and prepared Gd2W0.05Mo0.95O6:Eu3+ phosphors, was successfully fabricated. These results confirmed that the Eu3+-doped Gd2W1-xMoxO6 phosphors have potential value as the red component for WLEDs.

Luminescence characteristics and energy transfer of Eu2+/Tb3+ doped single phase multi-color phosphor

The investigation on single phase multi-color phosphors is highly meaningful for near-ultraviolet chip based white light emitting diodes. In this work, a series of Eu2+ and Tb3+ singly doped and Eu2+/Tb3+ codoped Sr5(PO4)3Cl phosphors were synthesized via a high-temperature solid state reaction method. The luminescence spectra and decay curves of Eu2+ and Tb3+ singly doped samples were discussed, the optimal doping concentrations were determined. Thanks to the spectra overlap between Eu2+ and Tb3+, nonradiative energy transfer from Eu2+ to Tb3+ was investigated. It is found electric dipole-dipole interaction played the main role for the energy transfer in codoped samples, the highest energy transfer efficiency was calculated to be 60.98%. Tunable emissions are observed for codoped samples by adjusting doping concentration. The thermal quenching properties were discussed and the activation energy (ΔE) was estimated in the present work.

High-efficiency and thermal-stable Ca3La(GaO)3(BO3)4:Eu3+ red phosphors excited by near-UV light for white LEDs

The Ca3La(GaO)3(BO3)4:Eu3+ (CLGB:Eu3+) red-emitting phosphors with high-efficiency and splendid thermal stability were prepared by a solid-state method. The synthesized samples were analyzed by X-ray diffraction, photoluminescence spectra, fluorescence decay curves, temperature-dependent photoluminescence spectra, diffuse reflection spectra and internal quantum efficiency. All the CLGB:Eu3+ compounds showed strong red emission peaking at around 621 nm under 397 nm excitation and the best doping concentration was 60 mol%. What's more, CLGB:Eu3+ phosphors also displayed excellent thermal stability and the emission intensity at 423 K maintained 78.6% of original value at 303 K. Furthermore, the internal quantum efficiency of the resultant phosphors reached up to 82.2%. By combining a near-ultraviolet chip, (Ba,Sr)2SiO4:Eu2+ green-emitting phosphors, BaMgAl10O17:Eu2+ blue-emitting phosphors and CLGB:0.6Eu3+ red-emitting phosphors, the fabricated light-emitting diode can generate bright white light with low correlated colour temperature of 3964 K and high colour rendering index of 85. All of these achieved results demonstrate that the CLGB:Eu3+ compounds are potential red-emitting phosphors for the near-ultraviolet chip excited white light-emitting diodes.

Highly Efficient Blue Emission and Superior Thermal Stability of BaAl12O19:Eu2+ Phosphors Based on Highly Symmetric Crystal Structure

Highly efficient phosphor materials with superior thermal stability are indispensable for phosphor-converted white light-emitting diodes (pc-WLEDs) solid state lighting. In order to obtain a high quality warm white light, near-ultraviolet (n-UV) chips combined with trichromatic phosphors have be extensively studied. Among them, the development of efficient blue phosphor remains a challenging task. In view of the close correlation between 5d–4f transitions of rare earth ions and the coordination environment of host lattice, many studies have been dedicated to improving the photoluminescence performances by modifying the lattice coordination environment including the lattice rigidity and symmetry. In this work, we reported highly efficient blue-emitting Eu2+-doped BaAl12O19 (BAO) phosphors with excellent thermal stability, which were prepared via the traditional high-temperature solid state reaction routes. According to the X-ray powder diffraction (XRD) Rietveld refinement analysis, BAO owned a highly symm...

Tunable luminescent spectra via energy transfers between different lattice sites in Ce3+, Mn2+ codoped Ba9Lu2Si6O24 phosphors for NUV-based warm white LED applications

A series of Ce3+–Mn2+ codoped Ba9Lu2Si6O24 (BLS) were synthesized by high-temperature solid-state reactions. The 380–410 nm excitation band of Ce3+ at the Lu sites (Ce(1)) matches well with the emission light of commercial near-ultraviolet (NUV) light-emitting diode (LED) chips. Under the Ce(1) excitation, BLS:Ce3+, Mn2+ exhibited a tunable emission from blue–green to yellow–orange via energy transfers (ETs) from Ce(1) to Mn2+. The ET was demonstrated to be of the resonant type via a dipole–quadrupole mechanism. At room temperature (RT), the optimal internal and external quantum efficiencies (QEs) of BLS:Ce3+, Mn2+ were determined as 79 and 42%. At 150 °C, 85% of the RT QE still can be remained, showing a high thermal stability. A warm white LED (WLED) with a color rendering index of 84 and a correlated color temperature of 3660 K was obtained by combining a 395 nm NUV chip with the phosphor and CaAlSiN3:Eu2+. The efficiency reaches 17 lm W−1 at 20 mA, which is better than the value of most NUV-based WLEDs. These results indicate the promising application of the phosphor as an attractive candidate for WLEDs.

A broad band yellow-emitting Sr8CaBi(PO4)7:Eu2+ phosphor for n-UV pumped white light emitting devices

A novel broad band yellow-emitting Sr8CaBi(PO4)7:Eu2+ (SCBP:Eu2+) phosphor was synthesized via conventional high-temperature solid-state reaction. It's crystal structure and phase were investigated with X-ray diffraction (XRD), Rietveld refinement method and transmission electron microscopy (TEM). The photoluminescence spectra as well as fluorescence decay curves were measured and discussed. The SCBP:Eu2+ phosphor can exhibit a broad excitation band in the range from 260 to 425 nm, while the emission spectrum exhibits a broad asymmetric yellow emission band peaking at 606 nm under 400 nm excitation. By analyzing their structure and fluorescence decay lifetimes, five different Eu2+ luminescence centers in SCBP:Eu2+ phosphor were confirmed. Then the concentration quenching mechanism as well as the thermal stability has been discussed in detail. Furthermore, a white LED lamp which can exhibit good performance has been fabricated via combining a 400 nm near-ultraviolet (n-UV) chip with the commercial BAM:Eu2+ phosphor and the present SCBP:0.04Eu2+ sample. These results suggest that the SCBP:Eu2+ can be a promising yellow-emitting n-UV phosphor for white light emitting diodes.

Self-activated multicolor emissions in Ca2NaZn2(VO4)3:Eu3+ phosphors for simultaneous warm white light-emitting diodes and safety sign

Self-activated Eu3+-doped Ca2NaZn2(VO4)3 multicolor-emitting phosphors were prepared by a facile critic-assisted sol-gel technique. Both the photoluminescence (PL) excitation and three-dimensional PL emission spectra revealed that the synthesized samples exhibited an intense absorption band in the range of 250–370 nm. The emission intensity of the phosphors was greatly dependent on the doping concentration and the optimal value was found to be 7 mol%. The concentration quenching mechanism is attributed to the dipole-dipole interaction and the critical distance is 18.8 Å. With the addition of Eu3+ ions, multicolor emissions were observed in the resultant phosphors when excited at 290 nm. The thermal stability of phosphors was characterized by temperature-dependent PL emission spectra. By manipulating the temperature, the emitting color of the prepared phosphors was tuned from yellowish red to orange, and ultimately to pure red. Additionally, the near-ultraviolet (NUV) chip-based light-emitting diode device, which was fabricated by coating the blended resultant phosphors, commercial blue-emitting and green-emitting phosphors on the NUV chip, emitted glaring warm white light with superior color rendering index and impressive correlated color temperature. These results suggest that the self-activated Eu3+-doped Ca2NaZn2(VO4)3 multicolor-emitting phosphors are suitable for safety sign in high temperature circumstance and indoor lighting.

A Potential Red-Emitting Phosphor BaZrGe3O9:Eu3+ for WLED and FED Applications: Synthesis, Structure, and Luminescence Properties.

A variety of Eu3+-activated BaZrGe3O9 phosphors was synthesized via solid-state reaction. The phase formation of BaZrGe3O9:Eu3+ samples was verified by powder X-ray diffraction analysis, while Rietveld refinement method was used to confirm the crystal structure. The electronic structure and characteristic photoluminescence as well as cathodoluminescence properties were researched in detail. The samples show strong absorption at 394 nm, which matches well with the commercial near-ultraviolet chips. Under 394 nm excitation, the phosphors exhibit the characteristic emissions of Eu3+ ions consistent with the 5D0-7FJ transitions. Then we investigated the thermal stability detailedly. The temperature-dependent photoluminescence emission spectra suggest that the obtained phosphors have favorable thermal stability. A white light-emitting diode (WLED) lamp with low correlated color temperature and good color render index was fabricated with blue-emitting BaMgAl10O17:Eu2+, green-emitting Sr2SiO4:Eu2+ (commercial), and red-emitting BaZrGe3O9:Eu3+ phosphors in near-ultraviolet light-emitting diodes (λmax = 395 nm) as well. Furthermore, the phosphor also exhibits red emission with high resistance and high current saturation under low voltage electron bombardment. It has better degradation resistance than the commercial Y2O3:Eu phosphor. All the results manifest that the Ba0.88Eu0.08ZrGe3O9 phosphor can be an eligible red-emitting phosphor candidate for WLEDs and field-emission displays.

Synthesis and photoluminescence properties of Eu2+ activated CaO ceramic powders for near-ultraviolet chip based white light emitting diodes

In this paper, we synthesized series of Eu2+ activated CaO ceramic powders by conventional solid state reaction. Using NH4Cl as a reducing additives, the Eu3+ has been successfully reduced to Eu2+. An intense blue emission peaked at 460 nm from Eu2+ was observed. The luminescent intensity of the doping-optimized CaO:Eu2+ sample can be as high as 106% of commercial BAM blue phosphor under 400 nm near-ultraviolet (NUV) excitation. The effect of Eu2+ and NH4Cl contents on photoluminescence properties and crystal phase formation have been investigated, respectively. The thermal stable property which is an important performance for LED application has also been measured. The emission intensity at 120 °C can maintain 94% of that at room temperature. Our results suggest that CaO: Eu2+ ceramic powder could be used as a promising blue emitting phosphor for NUV chip based white LEDs.

Sol-gel synthesis and luminescence property of Sr4 Al2 O7 :Re3+ ,R+ (Re=Eu and Dy; R=Li, Na and K) phosphors for white LEDs.

Sr4 Al2 O7 :Eu3+ and Sr4 Al2 O7 :Dy3+ phosphors with alkali metal substitution were prepared using a sol-gel method. The effects of a charge compensator R on the structure and luminescence of Sr4 Al2 O7 :Re3+ ,R+ (Re=Eu and Dy; R=Li, Na and K) phosphors were investigated in detail. Upon heating to 1400°C, the structure of the prepared samples was that of the standard phase of Sr4 Al2 O7 . Under ultraviolet excitation, all Sr4 Al2 O7 :Eu3+ ,R+ samples exhibited several narrow emission peaks ranging from 550 to 700nm due to the 4f→4f transition of Eu3+ ions. All Sr4 Al2 O7 :Dy3+ ,R+ phosphors showed two emission peaks at 492 and 582nm, due to the 4 F9/2 →6 H15/2 and 4 F9/2 →6 H13/2 transitions of Dy3+ ions, respectively. The luminescence intensity of Sr4 Al2 O7 :Re3+ ,R+ (Re=Eu and Dy; R=Li, Na and K) phosphors improved markedly upon the addition of charge compensators, promoting their application in white light-emitting diodes with a near-ultraviolet chip.

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350–420 nm). In this work, novel rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca2KZn2(VO4)3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO4:Eu2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K.

Crystal structure and luminescence properties of the blue-green-emitting Ba9 (Lu, Y)2 Si6 O24 :Ce3+ phosphor.

Samples of the Ba9 (Lu2-x Yx )Si6 O24 :Ce3+ (x=0-2) blue-green phosphors were synthesized by solid-state reactions. All the samples exhibited a rhombohedral crystal structure. As the Y3+ concentration increased, the diffraction peaks shifted to the small angle region and the lattice parameters increased due to the larger ionic radius of Y3+ (r=0.900Å) compared with that of Lu3+ (r=0.861Å). Under 400nm excitation, samples exhibited strong blue-green emissions around 490nm. The emission bands had a slight blue shift that resulted from weak crystal-field splitting with increasing Y3+ concentration. Luminescence intensity and quantum efficiency (QE) decreased with increasing Y3+ concentration. The internal QE decreased from 74 to 50% and the external QE decreased from 50 to 34% as x increased from 0 to 2. The thermal stability of the Lu series was better than that of the Y-series. The excitation band peak around 400nm matched well with the emission light from the efficient near-ultraviolet (NUV) chip. These results indicate promising applications for these NUV-based white light-emitting diodes.

Sol-gel synthesis of Eu3+/Bi3+ ions co-doped BaLa2WO7 phosphors for red-LEDs under NUV excitation and FEDs applications

Eu3+ ions single-doped and Eu3+/Bi3+ ions co-doped BaLa2WO7 (BLWO) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction patterns confirmed their monoclinic phase with a space group P21/b after annealing at 1350°C. The morphological properties of the prepared BLWO: 0.09mol Eu3+ (i.e., BLWO:0.09Eu3+) and BLWO:0.09Eu3+/0.01Bi3+ phosphors were observed by field-emission scanning electron microscope and transmission electron microscope images. Under near-ultraviolet (NUV) excitations, the photoluminescence (PL) properties were investigated for the BLWO:Eu3+ and BLWO:Eu3+/Bi3+ phosphors. The PL results suggest that the both phosphors showed an intense characteristic red emission at 616nm due to the 5D0 → 7F2 electronic transition. The existence of energy transfer mechanism in between Bi3+ and Eu3+ ions was explained by their decay curves. Additionally, temperature-dependent PL emission spectra and quantum yield were studied for the optimized phosphor. By combing a 399nm NUV chip with the BLWO:0.09Eu3+/0.01Bi3+ phosphor, a red light-emitting diode was implemented. Furthermore, the cathodoluminescence (CL) properties were analyzed for the BLWO:0.09Eu3+ and BLWO:0.09Eu3+/0.01Bi3+ phosphors as a function of accelerating voltage and filament current. To estimate the CL potentiality, the BLWO:0.09Eu3+/0.01Bi3+ phosphor was compared with a commercial Y2O3:Eu3+ red phosphor. The Commission International de I-Eclairage chromaticity coordinates were calculated for the optimized phosphor samples.

Luminescence properties of LiY6O5(BO3)3:Eu3+/Sm3+ phosphor

Abstract Eu 3+ , Sm 3+ single-doped and co-doped LiY 6 O 5 (BO 3 ) 3 phosphors are prepared by a high-temperature solid-state reaction method. The Eu 3+ -doped and Sm 3+ -doped phosphors give bright red emission centered at 613 and 604 nm under 395- and 406-nm excitation, respectively, while the Eu 3+ , Sm 3+ co-doped phosphor just gives Eu 3+ -characterized emission whether excited by 395 or 406 nm. This indicates that the co-doped Sm 3+ ions can broaden the excitation band of the phosphor without changing its color index, which might match better with the near-ultraviolet (NUV) chips in white light-emitting diode (W-LED) application. The Sm 3+ -concentration-dependent luminescence properties ascribed to the energy transfer between Eu 3+ and Sm 3+ is discussed.

Red emitting phosphors of Eu3+ doped Na2Ln2Ti3O10 (Ln = Gd, Y) for white light emitting diodes

A series of Eu3+ doped Na2Ln2Ti3O10 (Ln=Gd, Y) red-emitting phosphors for application in ultraviolet based light emitting diodes (LEDs) were successfully synthesized by a modified sol–gel method. Their structure and luminescent properties were characterized by powder X-ray diffraction (XRD), photoluminescence excitation (PLE) and emission (PL) spectra and absorption spectra, according to these results the optimal compositions and synthesis parameters were determined. In addition, the thermal stabilities of the phosphors were investigated according to the temperature-dependent PL spectra. The red and white-LEDs (W-LEDs) comprising the Na2Ln2Ti3O10:Eu3+ (Ln=Gd, Y) red emitting phosphors were fabricated with a near-ultraviolet (n-UV) chip. In comparison with Na2Y1.4Eu0.6Ti3O10, the Na2Gd0.6Eu1.4Ti3O10 phosphor offers higher brightness, quantum efficiency, and excellent thermal stability. W-LEDs comprising Na2Gd0.6Eu1.4Ti3O10 showed bright white emission with a color rendering index (Ra) of 82, a color temperature of 2151K, and Commission Internationale de I’Eclairage (CIE) color coordinates of (0.34, 0.37). The phosphor Na2Gd0.6Eu1.4Ti3O10 is more suitable candidate for application in LEDs.

Photoluminescent properties of Sr2CeO4 : Eu3+ and Sr2CeO4 : Eu2+ phosphors suitable for near ultraviolet excitation

Powder phosphors of 1 mol% Eu3+- and Eu2+-doped strontium cerium oxide (Sr2CeO4) were synthesized by standard solid-state reaction method. Eu3+- and Eu2+-doped Sr2CeO4 phosphors fired at 1100 °C for 2 h were analysed by X-ray diffraction (XRD) and photoluminescence (PL) techniques. The XRD patterns confirm that the obtained phosphors are a single phase of Sr2CeO4 composed of orthorhombic structure. Room temperature PL excitation spectrum of air-heated Sr2CeO4 : Eu phosphor has exhibited bands at 260, 280 and 350 nm. Whereas the excitation spectrum of Sr2CeO4 : Eu phosphor heated under reducing (carbon) atmosphere exhibited single broadband range from 260 to 390 nm. The (PL) emission peaks of both the phosphors at 467 (blue), 537 (green) and 616 nm (red) generate white light under 260, 280 and 350 nm excitation wavelengths. The Commission International de l’Eclairage (CIE) colour coordinates conforms that these phosphors emitting white light. The results reveal that these phosphors are multifunctional phosphors which emit white light under these excitations that they could be used as white components for display and lamp devices and as well as possible good light-conversion phosphor LEDs under near-ultraviolet (nUV) chip.

Ca3Si2O4N2:Ce3+,Li+ Phosphor for the Generation of White‐Light‐Emitting Diodes with Excellent Color Rendering Index Values

AbstractBlue‐emitting Ca3Si2O4N2:Ce3+,Li+ phosphors were successfully synthesized by solid‐state reactions for applications in white near‐ultraviolet (NUV) light‐emitting diodes (LEDs) with excellent color rendering index (CRI) values. The excitation and reflectance spectra of these phosphors reveal broad excitation and absorption in the NUV region, which matches well with those of NUV chips. This phosphors showed a broad blue emission at 436–488 nm that is dependent on the concentration of Ce3+ and Li+ ions; the quantum efficiency of (Ca0.94Ce0.03Li0.03)3Si2O4N2 is 23.6 % of that of the Ca5(PO4)3Cl:Eu2+ phosphor. The thermal stability of the (Ca0.94Ce0.03Li0.03)3Si2O4N2 phosphor below 100 °C was higher than that of the commercially available Ca5(PO4)3Cl:Eu2+ phosphor, and the activation energies were calculated to be 0.0445 and 0.0205 eV for the (Ca0.94Ce0.03Li0.03)3Si2O4N2 and Ca5(PO4)3Cl:Eu2+ phosphors. The optical properties of the white NUV LED gave an excellent CRI of 92.5 with International Commission on Illumination (CIE) chromaticity coordinates of (0.338, 0.345) at a correlated color temperature (CCT) of 5266 K.

Luminescence properties of red-emission Mg4 Nb2 O9:Eu3+ phosphor.

Red-emitting Mg4 Nb2 O9 :Eu(3+) phosphor is synthesized via a solid-state reaction method in air, and its crystal structure and luminescence are investigated. The phosphor can be excited efficiently by ~ 395 nm light, coupled well with a ~ 395 nm near-ultraviolet chip and emits red light at ~ 613 nm with sharp spectra due to (5) D0 → (7) F2 transition of the Eu(3+) ion. Mg4 Nb2 O9 :Eu(3+) phosphor sintered at 1350 ºC shows Commission international de I'Eclairage (CIE) chromaticity coordinates of x = 0.6354, y = 0.3592, and is a potential red-emitting phosphor candidate for white light-emitting diodes (W-LEDs) under ~ 395 nm near-ultraviolet LED chip excitation.

Tunable luminescence properties and efficient energy transfer in Eu2+, Tb3+ co-doped NaBaPO4

Eu2 + and Tb3+ singly doped and co-doped NaBaPO4 phosphors were synthesized by solid state reaction. The structure character, photoluminescence properties and the lifetime were investigated. The emission spectra of NaBaPO4:Eu2+, Tb3+, Na+ phosphor show both broad blue emission band and sharp green emission peaks. The energy transfer mechanism from Eu2+ to Tb3+ in NaBaPO4 host was discussed. The excitation spectra of NaBaPO4: Eu2+, Tb3+, Na+ phosphor show broad excitation band in the 250–400nm range, which was in agreement with the near-ultraviolet (n-UV) chip. The hue of the NaBaPO4: Eu2+, Tb3+, Na+ phosphors could be appropriately tuned by adjusting the contents of activators.

New orange–red phosphor Sr9Sc(PO4)7:Eu3+ for NUV-LEDs application

• A novel orange–red phosphor Sr 9 Sc(PO 4 ) 7 :Eu 3+ has been synthesized and investigated. • The phosphors can be effectively excited by near UV (394 nm) light. • The thermal quenching temperature of Sr 9 Sc(PO 4 ) 7 :Eu 3+ is above 200 °C. A series of Eu 3+ ions doped Sr 9 Sc(PO 4 ) 7 orange–red emitting phosphors have been prepared by solid-state reaction method. Photoluminescence properties under near-ultraviolet (NUV) light excitation of the samples have been carried out. The studies show that the samples can be effectively excited by NUV (394 nm) which matches to the output wavelengths of near UV chips and exhibits intense orange–red emissions. Eu 3+ concentration was found to be optimum at x = 0.4 and the thermal quenching temperature of Sr 9 Sc(PO 4 ) 7 :0.4Eu 3+ is above 200 °C. Thus, the intense orange red emitting phosphor could be a promising phosphor candidate in generating white light combined with the NUV chip.