Luminescent properties of Ca_2SiO_4:Eu^(3+) red phosphor for trichromatic white light emitting diodes

The luminescent properties of Eu^3＋doped Ca2SiO4 red phosphors synthesized by the flux fusion reaction method were investigated. It was found that the excitation spectrum included two regions： the weak excitation band below 325 nm and strong narrow peaks above 325 nm. The main peak of the excitation band was located at 400 nm. The peaks located at 290 nm were assigned to the combination of the charge transfer transition of O-Eu, peaks above 325 nm （325, 385, 400, 470, 511, and 539 nm） were assigned to the f-f transitions of Eu^3＋. The emission spectrum was dominated by the red peak located at 612 nm due to the electric dipole transition of ^5D0-^7F2. In addition, the effects of the Eu^3＋ content and charge compensators of Li^＋, Na^＋, K^＋, and Cl^- ions on the emission intensity were investigated. The experiment results suggested that the strongest emission was obtained when the concentration of the Eu^3＋ ions was 0.3 mol^-1, and Li^＋ ions gave the best improvement to enhance the emission intensity. Ca2SiO4：Eu^3＋, Li^＋ was thus suitable for low-cost trichromatic white light emitting diodes （WLED） based on UV InGaN chip.

Potential red-emitting phosphor GdNbO_4:Eu^(3+),Bi^(3+) for near-UV white light emitting diodes

A red-emitting phosphor GdNbO4：Eu3＋,Bi3＋ was prepared by a high temperature solid-state reaction technique. The phosphor was characterized by X-ray diffraction （XRD）, particle size analyzer and fluorescence spectrometer. The single phase of GdNbO4：Eu3＋,Bi3＋ was obtained at 1150~C and the average particle diameter was about 2.30 μm. Excitation and emission spectra reveal that the phosphor can be ef- ficiently excited by ultraviolet （UV） light （394 nm） and emit the strong red light of 612 nm due to the Eu3＋ transition of SD0~TF2. The opti- mum content of Eu3＋ doped in the phosphor GdNbOn：Eu3＋ is 20mo1%. The phosphor Gdo.80NbO4：0.20Eu3＋,0.03Bi3＋ shows much stronger photoluminescence intensity and better chromaticity coordinates （x=0.642, 0.352） than GdNbO4：Eu3＋. It is confirmed that Gdo.80NbO4：0.20Eu3＋,0.03Bi3＋ is a potential candidate for near-UV chip-based white light emitting diodes.

Red Emitting Phosphor (Y,Gd)BO_3:Eu^(3+) for PDP Prepared by Complex Method

Red phosphor (Y, Gd)BO3:Eu3+ with grain shape, small size, non-agglomerate, high crystallinity and good photoluminescence (PL) intensity was prepared by a complex method that the precursor of the phosphor was prepared by co-precipitation method and the phosphor was prepared by combustion method. The SEM photos and the photoluminescence spectrum excited under VUV show that the morphology and luminescent properties of this phosphor are satisfied when an appropriate amount of urea was adopted as the combustion agent in the preparation procedure.

A red oxide phosphor,Sr_2ScAlO_5:Eu^(2+) with perovskite-type structure,for white light-emitting diodes

Sr2ScAlO5：Eu^2＋, a red oxide phosphor with a perovskite-type structure, has been synthesized through a solid-state reaction and its luminescence properties have been investigated. An absorption band centering at 450 nm is observed from the diffuse reflection spectra and the excitation spectra, indicating that the phosphor can match perfectly with the blue light of InGaN light-emitting diodes. A broad red emission band at 620 nm is found from the emission spectra, originating from the 4f^65d-4f^7 transition of the Eu^2＋ ions. The best doping content of Eu in this material is about 5%. S Sr2ScAlO5：Eu^2＋ is a highly promising red phosphor for use in white light-emitting diodes.

Preparation and Characterization of Red Emitting Phosphor Ba_xCa_(3-x)(PO_4)_2∶Ce, Mn

Red emitting phosphor （BaCa）3 （PO4）2 ： Ce, Mn was prepared by solid state reactions. Effect of chemical component, preparation conditions on the performance of the phosphor was studied by using TGDTG, XRD and phosphor relative brightness meter. It is found that the host （ Bax Ca1-x ） 3 （PO4） 2 is present as a distorted Ca3（PO4）2 structure. Ce^3＋ acts as a sensitiser, and Mn^2＋ is activator. By energy transfer from Ce^3＋ to Mn^2＋, Mn^2＋ is activated and emits red light with wavelength around 650 nm. The phosphor powder shows the highest emitting brightness, when the con- centrations of Ce^3＋and Mn^2＋ are both at 0.15 mol.

Luminescence properties of red-emitting Ca_2Al_2SiO_7:Eu^(3+) nanoparticles prepared by sol-gel method

A series of red-emitting Ca2_xA12SiOT：xEu^3＋ （x = 1 mol.%-10 tool.%） phosphors were synthesized by the sol-gel method. The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2A12SiO7：Eu^3＋ phosphors were investigated. X-ray diffraction （XRD） profiles showed that all peaks could be attributed to the tetragonal Ca2A12SiO7 phase when the sample was annealed at 1000℃. Scanning electron microscopy （SEM） micrographs indicate that the phosphors have an irregularly rounded mor- phology with particles of about 200 nm. Excitation spectra showed that the strong broad band at around 258 nm and weak sharp lines in 350-490 nm were attributed to the charge transfer band of Eu^3＋-O^2- and f-f transitions within the 4f^6 configuration of Eu^3＋ ions, respectively. Emission spectra implied that the red luminescence could be attributed to the transitions from the ^5D0 excited level to the 7Fj （J = 0, 1, 2, 3, 4） levels of Eu3＋ions with the main electric dipole transition ^5D0→^7F2 （618 and 620 nm）, and Eu^3＋ ions prefer to occupy a lower symmetry site in the crystal lattice. Moreover, the photoluminescence （PL） intensity was strongly dependent on both the sintering temperature and doping concentration, and the highest PL intensity was observed at an Eu^3＋ concentration x = 7 mol.% after annealing at ll00℃. The obtained Ca2A12SiO7：Eu^＋3＋ phosphor may have potential application for the red lamp phosphor.

Bi-and Eu-Doped Y_2O_3 Phosphors for Ultraviolet Light Emitting Diodes

The bismuth and europium activated Y2O3 red phosphors and were investigated their structure and optical properties. Adding bismuth ions enhance the energy absorption between 300 nm and 400 nm of Eu-doped Y2O3 excitation spectra. The reason may be the energy transfer from bismuth to europium ions.

A novel yellow emitting phosphor Dy^(3+),Bi^(3+) co-doped YVO_4 potentially for white light emitting diodes

Novel Y1-x-yVO4：xDy3＋, yBi3＋ （0.01 ≤ x ≤ 0.05,0 ≤ y ≤0.20） phosphors for light emitting diode （LED） were successfully synthesised by solid-state reaction. The calculation results of electronic structure show that YVO4 has a direct band gap with 3 eV at G. The top of the valence band is dominated by O 2p state and the bottom of the conduction band is mainly composed of O 2p and V 3d states. An efficient yellow emission under near-ultraviolet （365 nm） excitation is observed. Compared with the pure YVO4：Dy3＋ samples, the Dy3＋, Bi3＋ co-doped samples show a more intensive emission peak （at 574 nm） and a new broad emission band （450-770 nm）, due to the 4F9/2 - 6H13/2 transition of Dy3＋ and the emission of the VO43-Bi3＋ complex respectively. The optimum chromaticity index of Y1-x-yVO4：xDy3＋, yBi3＋ （0.01 ≤ x ≤0.05,0 ≤y ≤ 0.20） is （0.447, 0.497）, which indicates that YVO4：Dy3＋, Bi3＋ has higher colour saturation than the commercial phosphor YAG： Ce3＋. The effects of concentration of Dy3＋, Bi3＋, electric states and the photoluminescence properties are discussed in details.

Si/Al order and texture orientation optimization of red-emitting Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics for laser phosphor display

Laser phosphor display technology plays an important role in advanced display projection;however,it is a challenge in maintaining excellent color accuracy under high brightness due to the lack of red spectrum.Here,red-emitting Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics as the phosphor wheel have been optimized in chemical compositions and texture orientation.The textured Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics have high transparency and spot limiting ability,accordingly,the ceramic wheel outputs 1,184 lm of ultra-bright red light under 50 W/mm^(2) laser power density.Moreover,the red spectral utilization(over 600 nm)of textured Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)ceramics is 2.17 times that of traditional Y3Al5O12:Ce^(3+)phosphor wheel.The red-emitting textured Mg_(2)Al_(4)Si_(5)O_(18):Eu^(2+)cordierite ceramic herein enables an improved light-color saturation experience,and it is potential in the next-generation laser phosphor display applications.

Synthesis and Luminescence Improvement of CaAlSiN_(3)Phosphors Doped with Eu^(2+)and Mn^(2+)for White LEDs

Eu^(2+)and Mn^(2+)co-activated CaAlSiN_(3)red phosphors were produced using the solid-state reaction tech⁃nique in a N2 environment.Excitation spectra,emission spectra,and diffuse reflection spectra were used to study the luminescence characteristics,energy gap,and thermal stability in detail.CaAlSiN_(3)∶Eu^(2+)exhibits an extended emission band when stimulated with 450 nm blue light,which is caused by the 4f65d to 4f7 transition of Eu^(2+).Similar⁃ly,CaAlSiN_(3)∶Mn^(2+)displays a wide emission band centered at 628 nm,which results from Mn^(2+)’s transition from 4T1(4G)to 6A1(6S).When the ions of Mn^(2+)were combined into CaAlSiN_(3)∶Eu^(2+),the photoluminescence intensity of Eu^(2+)was greatly boosted because there was energy transfer and co-emission between Mn^(2+)and Eu^(2+).Beyond that,CaAlSiN_(3)∶Eu^(2+),Mn^(2+)emerges with splendid thermostability and high quantum efficiency,the quenching temperature surpasses 300℃,and the internal quantum efficiency is determined to be around 84.9%.The white LED was pack⁃aged with a combination of CaAlSiN_(3)∶Eu^(2+),Mn^(2+),LuAG∶Ce3+and a blue chip.At a warm white-light corresponding color temperature(3009 K)with CIE coordinates(0.4223,0.3748),the color rendering index Ra has reached 93.2.CaAlSiN_(3)∶Eu^(2+),Mn^(2+)would have great application potential as a red-emitting phosphor for white LEDs.

Silica encapsulated ZnO quantum dot-phosphor nanocomposites:Sol-gel preparation and white light-emitting device application

ZnO quantum dots （QDs） as an eco-friendly and low-cost material has bright fluorescence, which makes it promising material for healthy lighting and displaying. However, the low fluorescence efficiency and poor stability of ZnO QDs impede their applications in lighting application. In this work, silica encapsulated ZnO QD-phosphors nanocomposites （ZSPN） have been prepared through a sol-gel synthesis process, where yellow-emitting ZnO QDs and blue-emitting BaMgAl10O17：Eu2＋ are employed as the luminescence cores and silica as link between two luminescence materials. Tunable photoluminescence of ZSPN and the white light emission have been achieved through changing mass ratio of both of ZnO QDs and commercial phosphors. The PLQY of the ZSPN can reach 63.7% and they can maintain high luminous in- tensity even the ambient temperature up to 110 ℃ and after 35 h of UV irradiation. In addition, they can keep stable for 40 days. By coating the ZSPN phosphors onto a ultraviolet chip, WLEDs with luminous efficiency of 73.6 lm/W and the color coordinate, correlated color temperature, and color rendering index can reach （0.32, 0.34）, 5580 K, and 87, respectively, indicating the bright prospect of the ZSPN phosphors used in healthy lighting.

Phosphor-free white light-emitting diodes

The multiple color-matching schemes that could improve the color rendering index for phosphor-free white LEDs are discussed. Then we review a few of the recent research directions for phosphor-free white LEDs, which include the development of monolithic GaN-based white LEDs and hybrid integrated GaN-based and A1GalnP-based white LEDs. These development paths will pave the way toward commercial application of phosphor-free white LEDs in the coming years.

NOVEL RED LIGHT-EMITTING POLYMERS BASED ON 2,7-CARBAZOLE AND THIOPHENE DERIVATIVES

A series of conjugated copolymers derived from 9-ethylhexyl-2,7-carbazole(Cz)and 4,7-di(4-hexylthien-2-yl)- 2,1,3-benzothiadiazole(DHTBT)was synthesized by Suzuki polycondensation.The photo-and electro-luminescent properties of these polymers were investigated.Efficient energy transfer from the Cz segment to the DHTBT unit occurs even if the DHTBT content as low as 1 mol%.PL emission was red-shifted significantly from 645 nm to 700 nm with the increase in DHTBT content by 1-50 mol%.PL efficiencies decreased...

Color-converted remote phosphor prototype of a multiwavelength excitable borosilicate glass for white light-emitting diodes

We report a unique red light-emitting Eu-doped borosilicate glass to convert color for warm white light-emitting diodes. This glass can be excited from 394 nm-peaked near ultraviolet light, 466 nm-peaked blue light, to 534 nm- peaked green light to emit the desired red light with an excellent transmission in the wavelength range of 400-700 nm which makes this glass suitable for color conversion without a great cost of luminous power loss. In particular, when assembling this glass for commercial white light-emitting diodes, the tested results show that the color rendering index is improved to 84 with a loss of luminous power by 12 percent at average, making this variety of glass promising for inorganic ＂remote-phosphor＂ color conversion.

Luminescent properties of Lu_2MoO_6:Eu^(3+) red phosphor for solid state lighting

The Eu^3＋ activated Lu2MoO6 phosphors were synthesized by high-temperature solid-state reaction method. The X-ray diffraction （XRD）, excitation spectra, emission spectra and decay lifetime of the phosphors were measured to characterize the structure and luminescent properties. The XRD results show that all the prepared phosphors can be assigned to the monoclinic structure. The experimental results indicate efficient absorption of near ultraviolet light from the Mo^6＋O^2- group followed by intensive emission in the visible spectral range. The optimal content of Eu3＋ is 10% （mole fraction）. The critical distance Rc and energy transfer mechanism were also discussed in detail. This red emitting material may be applied as a promising red phosphor for the near ultraviolet excited white light emitting diodes.

Bi^(3+)-activated dual-wavelength emitting phosphors toward effective optical thermometry

Optical thermometry as an important local temperature-sensing technique,has received increasing attention in scientific and industrial areas.However,it is still a big challenge to develop luminescent materials with self-activated dual-wavelength emissions toward high-sensitivity optical thermometers.Herein,a novel ratiometric thermometric strategy of Bi^(3+)-activated dual-wavelength emission band was realized in the same lattice position with two local electronic states of La_(3)Sb_(1-x)Ta_xO_(7):Bi^(3+)(0≤x≤1.0)materials based on the different temperature-dependent emission behaviors,benefiting from the highlysensitive and regulable emission to the coordination environment of Bi^(3+).The structural and spectral results demonstrate that the emission tremendously shifted from green to blue with 68 nm and the intensity was enhanced 2.6 times.Especially,the visual dual-wavelength emitting from two emission centers was presented by increasing the Ta^(5+)substitution concentration to 20%or 25%,mainly originating from the two local electronic states around the Bi^(3+)emission center.Significantly,the dual-wavelength with different thermal-quenching performance provided high-temperature sensitivity and good discrimination signals for optical thermometry in the range between 303 and 493 K.The maximum relative sensitivity reached 2.64%/K(La_(3)Sb_(0.8)Ta_(0.2)O_(7):0.04Bi^(3+)@383 K)and 1.91%/K(La_(3)Sb_(0.75)Ta_(0.25)O_(7):0.04Bi^(3+)@388 K).This work reveals a rational design strategy of different local electronic states around the singledoping multiple emission centers towards practical applications,such as luminescence thermometry and white LED lighting.

Synthesis and luminescent properties of polycrystalline Gd_2(MoO_4)_3:Dy^(3+) for white light-emitting diodes

Polycrystalline Gd2(MoO4)3:Dy3+ phosphors have been synthesized by high temperature solid-state reaction method. The phosphors were characterized with X-ray diffractometer, thermogravimetric analysis and different scanning calorimeter, scanning electron microscopy, and photoluminescence spectrofluorimeter. Several peaks at 351, 389, 425, 452, and 472 nm appeared in photoluminescence excitation spectrum, which matched well with the emission of the ultraviolet (UV) and blue-light emitting diode (LED) chips. Upon excitation at 389 nm UV light, intense emissions centered at 484, 575 and 668 nm were attributed to the transitions of 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 of Dy3+, respectively. The chromaticity coordinates and correlative color temperatures have been calculated and presented in the Commission International de I’Eclairage (CIE) diagrams. The results indicated that Gd1.9(MoO4)3:Dy0.13+ with CIE coordinates of (x=0.38, y=0.41) and the correlative color temperature of 4134 K is a potential candidate for white LEDs.

Synthesis and Luminescence Properties of Red Phosphors:Mn^(2+) Doped MgSiO_3 and Mg_2SiO_4 Prepared by Sol-Gel Method

Sol-gel method was utilized to synthesize two different series of red silicate phosphors : MgSiO3 and Mg2SiO4 powder samples doped with Mn2+, conducted the investigation of red long-lasting phosphor: MgSiO3 : Eu2 + , Dy3+, Mn2+ . TGA curves of the gel precursor for two series depicted that the loss of residual organic groups and NO3 groups occurs below 450℃. According to the XRD patterns, the major diffraction peaks of the MgSiO3 and Mg2SiO4 series are consistent with a proto-enstatite structure (JCPDS No.11-0273) and a forsterite structure (JCPDS No.85-1364) respectively. With the excitation at 415 nm, the red emission band of Mn2+ ions is peaked at 661 nm for MgSiO3:1%(atom fraction) Mn2+ or 644 nm for MgiSiO4: 1 %(atom fraction) Mn2+ . Compared with Mg2SiO4:Mn2+ samples, MgSiO3:Mn2+ samples exhibit higher luminescence intensity and higher quenching concentration. In addition, the two series co-doped with Eu2+ , Dy3+ , Mn2+ were also prepared. Photo-luminescence and afterglow properties of the two co-doped series were analyzed, which show that MgSiO3: Eu2 + , Dy3+ , Mn2+ is more suitable for a red long-lasting phosphor.

Synthesis and luminescence properties of Ca_2SiO_4-based red phosphors with Sm^(3+) doping for white LEDs

Sm3＋-activated Ca2SiO4 red phosphors were prepared by the conventional high-temperature solid-state reaction method, and the effects of sodium （Na＋） and samarium （Sm3＋） ions doping concentrations on their crystal structure and luminescent properties were investigated by X-ray diffraction （XRD） and fluorescent spectrofluorometer. XRD patterns demonstrate that a well-crystalline structure forms in the phosphors when they are treated by calcination at 1200~C for 4 h, and the excitation spectra exhibit good absorption in the range between 350 and 420 nm. Under the irradiation of 405 nm near-ultraviolet （NUV） light, the spectra of the phosphors show a main emission peak at 601 nm attributed to the 4G5/2→6H7/2 transition of Sm3＋ ions, and its intensity is greatly influenced by the concentrations of Sm3＋ and Na2CO3. When the concentrations of Sm3＋ ions and Na2CO3 are 2mol% and 6mol%, respectively, the optimal emission intensity can be obtained. From strong absorption in the near ultraviolet zone, the Na0.06Sm0.02Ca1.92SiO4 phosphor is a promising red-emitting phosphor for white light emitting diodes （W-LEDs）.

Luminescence modification of Eu^(3+)-activated molybdate phosphor prepared via co-precipitation

Eu-activated CaMoO_(4)phosphors were co-precipitated in an aqueous solution,and NH_(3)·H_(2)O,NH_(4)HCO_(3)and(NH_(2))_(2)CO as pre-cipitating aid agents were compared based on the morphology and particle size distribution of the phosphor samples.Sm3+as sensitizer ion was investigated on the luminescence of CaMoO_(4):Eu,and it could strengthen the 406 nm absorption of this phosphor.At last,the scheelite CaMoO_(4):Eu and wolframite ZnMoO_(4):Eu were selected to compare their host absorption.The result showed that the scheelite molybdate host exhibited stronger UV absorption than wolframite one.