Long afterglow yellow luminescence from Pr3+ doped SrSc2O4

A yellow emitting long afterglow luminescence material SrSc₂O₄:Pr³⁺ was successfully prepared by solid state reaction method. SrSc₂O₄:Pr³⁺ phosphor shows a long afterglow luminescence peak at about 495, 545, 621, 630 and 657 nm, respectively, corresponding to the f–f transitions of Pr³⁺. The afterglow chromaticity coordinates of SrSc₂O₄:1 at%Pr³⁺ were calculated to be (0.35, 0.41), indicating that the afterglow emission is close to the light of yellow region. And, the afterglow luminescence of the optimal sample doped by 1 at%Pr³⁺ can persist for over 3 h. The thermoluminescence results suggest that there are three types of traps with depth of 0.61, 0.69 and 0.78 eV exiting for all the samples, which are produced by the addition of Pr³⁺ ions. The trap density of SrSc₂O₄:1 at%Pr³⁺ is the maximum when the incorporation of Pr³⁺ ions reaches 1 at%, which thus results in the longest afterglow luminescence. All the results indicate that SrSc₂O₄:Pr³⁺ can be a potential candidate of novel long afterglow phosphors.     

Synthesis and photoluminescence properties of a red emitting phosphor NaSr2（NbO3）5：RE3＋（RE=Sm,Pr） for white LEDs

Rare earth Sm3＋, Pr3＋doped NaSr2（NbO3）5 red phosphors were successfully synthesized. X-ray diffraction analysis indi-cated that all the samples were single phased. The luminescence property was investigated in detail by diffuse-reflectance spectra and photoluminescence spectra measurement. Both NaSr2（NbO3）5：Sm3＋and NaSr2（NbO3）5：Pr3＋phosphors showed strong absorption in near ultraviolet region, which was suitable for application in LEDs. When excited by UV light, they both emitted bright red emission with CIE chromaticity coordinates （0.603, 0.397） and （0.669, 0.330）, respectively. The optimal doping concentration of Sm3＋doped NaSr2（NbO3）5 was measured to be 0.04 and that for Pr3＋doped NaSr2（NbO3）5 was 0.01. The integral emission intensity was also measured and compared with the commercial red phosphor Y2O3：Eu3＋. The results indicated that NaSr2（NbO3）5：RE3＋（RE=Sm, Pr） have potential to serve as a red phosphor for UV pumped white LEDs.     

Green and red phosphor for LED backlight in wide color gamut LCD

Wide color gamut(WCG) backlight for liquid crystal display(LCD) utilizing white light-emitting diodes(LED) has attracted considerable attention for their high efficiency and color reduction.In this review,recent developments in crystal structure,luminescence and applications of phosphors for wide color gamut LED backlight are introduced.As novel red phosphors,Mn~(4+)activate fluoride and aluminate phosphors are advanced in quantum efficiency,thermal quenching and color saturation for their characteristic spectrum with broad excitation band and linear emission.The crystal structure and fluorescence properties of Mn~(4+)doped fluosilicate,fluorogermanate,fluotitanate,as well as Sr_4 Al_(14)O_(25),CaAl_(12)O_(19) and BaMgAl_(10)O_(17) phosphors are discussed in detail.A serial of narrow-band red-emitting Eu~(2+),Eu~(3+)and Pr~(3+)-doped nitride silicates and molybdate phosphors are also introduced.Rare-earth-doped oxynitride and silicate green-emitting phosphors have attracted more and more attention because of the wide excitation,narrow emission,high quenching temperature,high quantum efficiency,such as β-sialon:Eu~(2+),Ba_3Si_6O_(12)N_2:Eu~(2+),MSi_2O_2N_2:Eu~(2+)(M=Ca,Sr,Ba),y-AlON:Mn~(2+)and Ca_3Sc_2Si_3O_(12):Ce~(3+).All above phosphors demonstrate their adaptability in wide color gamut LCD display.Especially for Mn~(4+)doped fluosilicate red phosphor and β-sialon:Eu~(2+)green phosphor.To achieve an ultra-high color gamut in white LED backlight and against the OLED,innovative narrow-band-emission red and green phosphor materials with independent intellectual property rights are continuously pursed.     

Preparation,structure and luminescence properties of deep red phosphors SrSiN2:Eu2+

This paper reported a novel synthetic route to Eu2+ doped SrSiN2 deep red phosphors for white light-emitting diodes. A series of single-phased and high-efficiency Sr Si N2:Eu2+ red phosphors were synthesized based on this method. Their structure, morphology, luminescence, quantum efficiency(QE) and thermal quenching properties were investigated and compared with those of Sr Si N2: Eu2+ prepared by the conventional route. It was found that the addition of a small amount of Si3N4 could promote the formation of Sr Si N2 from Sr2Si5N8 phase. A highly uniform rod-shaped morphology was obtained based on this method. The X-ray powder diffraction and the Rietveld refinement analysis identified the preferential crystalline orientation growth. Under the blue light excitation, Eu2+ doped Sr Si N2 phosphors showed excellent optical properties. Compared with those prepared by the conventional approaches, the external QE of Sr Si N2:Eu2+ phosphor was greatly improved, allowing it a promising phosphor for white LEDs.     

Preparation of M2B5O9Cl:Eu2+(M=Sr,Ca) blue phosphors by a facile low-temperature self-reduction method and their enhanced luminescent properties

In this work,through a facile method of low-temperature(only 350 ℃) self-reduction,1D nano-sized M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) blue phosphors with highly efficient performance can be obtained.The crystal structure,morphology and photoluminescence(PL) properties including thermal stability of M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) phosphors were investigated.The M₂B₅O₉CI:Eu²⁺(M=Sr,Ca) phos...     

Photoluminescence properties of M2ZnSi2O7: Eu2+ (M=Sr,Ba)

The hardystonite phosphors of Eu²⁺ activated M₂ZnSi₂O₇ (M=Sr, Ba) were synthesized by combustion-assisted method. They were systematically characterized by photoluminescence excitation and emission spectra. The emission spectra of these two phosphors showed that the main emission peaks are at 475 and 503 nm due to 4f⁶5d¹→4f⁷ transition of Eu²⁺. Both phosphors could be efficiently excited in the wavelength range of 250-425 nm where the near ultraviolet light-emitting diode was well matched. The (x, y) color coordinates were determined with the emission values (x, y)=(0.41, 0.21) and (0.16, 0.45) for the M₂ZnSi₂O₇: Eu²⁺ (M=Sr, Ba) phosphors.     

Photoluminescent properties of tunable green-emitting oxynitride （Baa-xSrx）Si6012N2 ：Eu2＋ phosphor and its application in white LEDs

Green emitting Eu2＋-doped （Ba3_xSrx）Si6012N2 solid solutions were synthesized through solid state reaction at 1350 ℃ for 10 h under a N2/H2 atmosphere. The XRD patterns revealed that the solid solution series of （Ba3 x-ySrx）Si6Ol2N2：yEu2＋ with x value ranging from 0-0.6 were established. An efficient and intense tunable green light was observed by varying the cation Sr/Ba ratio. The emission spectra exhibited an entire shift towards long wavelength with increasing ofx value, which was caused by large crystal field splitting and Stokes shift. The x value dependence of emission intensity was discovered and explained by the enhanced probability of electron from excited 4f state to 5d ground state via nonradioactive transition. Highly thermal stability and feasible color coordinates were verified. White LEDs with excellent photochromic properties were fabricated by packing GaN based blue chips and （Ba Sr）3Si6012N2：Eu2＋ phosphors. All results indicated that the （Ba3_xSrx）SirO12N2：Eu2＋ phosphors were confirmed to be a promising candidate for pc-white LEDs in solid state lighting.     

Luminescence properties of Pr3+ and Bi3+ co-doped NaCaTiNbO6 phosphor for red-LEDs

This paper investigates the photoluminescence properties of NaCaTiNbO_6:Pr~(3+) and NaCaTiNbO_6:Pr~(3+),Bi~(3+) phosphors. NaCaTiNbO_6:Pr~(3+) and NaCaTiNbO_6:Pr~(3+),Bi~(3+) powder were synthesized successfully by solid state reaction method. Phase purity was checked using X-ray powder diffractometry(XRD). The excitation and emission spectra were recorded to elucidate the photoluminescence properties of NaCaTiNbO_6:Pr~(3+) and NaCaTiNbO_6:Pr~(3+),Bi~(3+). Furthermore,fluorescence lifetime measurements were performed. The excitation spectra of NaCaTiNbO_6:Pr~(3+) show a main band centered at around 357 nm.The luminescence spectra of NaCaTiNbO_6:Pr~(3+) exhibit a red emission peak at 615 nm from the ~1 D_2→~3 H_4 transition of Pr~(3+) ions. With the introduction of the Bi~(3+) ion into NaCaTiNbO_6:Pr~(3+), the luminescence intensity is enhanced nearly two times. Meanwhile,the absorption band edge of NaCaTiNbO_6:Pr~(3+) is shifted from 380 to 420 nm. Thus, this study shows that the red phosphor NaCaTiNbO_6:Pr~(3+) incorporated with Bi~(3+) is advantageous for light-emitting diode applications.     

Design of luminescence in(Sr,Gd)Li(Al,Mg)3N4:Eu2+ deep red phosphors via crystal field engineering for full-spectrum WLEDs

Red phosphor,with longer wavelength,is highly desirable for full-spectrum WLEDs.Targeted deep red phosphors(Sr,Gd)Li(AI,Mg)₃N₄:Eu²⁺ were designed from the initial model of SrLiAl₃N₄:Eu²⁺ by structural modification.The correlations among structural evolution,crystal-field environment,and luminescence properties were elucidated.Replacing Sr²⁺ with Gd³⁺in(Sr,Gd)LiAl₃N₄:Eu²⁺ leads...     

Enhanced photoluminescence of CaTiO3：Eu3＋ red phosphors prepared by H3BO3 assisted solid state synthesis

CaTiO₃:Eu³⁺ red phosphors were prepared using H₃BO₃ assisted solid state synthesis. The structure and morphology of the obtained sample were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). And the luminescence property was measured using photoluminescence excitation (PLE) and photoluminescence (PL) spectra, respectively. In the excitation spectra, main excitation peaks of the prepared samples were centered at 397 and 465 nm, revealing that these phosphors could be excited by commercial GaN- and InGaN-typed light emitting diodes (LEDs). Dominant emission peaks of the phosphors were located at 616 nm, owing to the transition of ⁵D₀→⁷F₂ of Eu³⁺. In the optimum condition, CaTiO₃:3%Eu³⁺ phosphor was obtained at a sintering temperature of 1200 °C in air with a content of 20 mol.% H₃BO₃ addition. When excited by 397 nm irradiation, the PL intensity of as-prepared red phosphor was 2.2 times higher than that of samples obtained by traditional solid state synthesis, while the PL intensity was 3 times higher than that excited by 465 nm irradiation. The added H₃BO₃ improved the crystallinity, and increased the color purity, implying the potential to be a promising red phosphor in white light emitting diodes (WLEDs).     

Eu2+-doped Sr5(PO4)3Br blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Eu²⁺-doped bromophosphateapatite Sr₅(PO₄)₃Br phosphors were synthesized by the conventional high-temperature solid-state reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal stability and CIE chromaticity coordinates were systematically investigated. Photoluminescence spectra of Sr₅(PO₄)₃Br:Eu²⁺ exhibit a single blue emission at 450 nm under the excitation of 345 nm, which is ascribed to the 4f–5d transition of Eu²⁺. The phosphor shows very good thermal stability. The CIE color coordinates are very close to those of BaMgAl₁₀O₁₇:Eu²⁺ (BAM). All the properties indicate that the blue-emitting Sr₅(PO₄)₃Br:Eu²⁺ phosphor has potential application in white LEDs.     

Enhanced luminescence efficiency and thermal stability via introduction of non-rare earth Bi3+ in Gd5Si2BO13:Eu3+

A series of Gd₅Si₂BO₁₃:Eu³⁺ and non-rare earth Bi³⁺ ions doped Gd₅Si₂BO₁₃:Eu³⁺ phosphors was successfully synthesized via high-temperature solid-state method,and the as-obtained phosphors were studied on their phase structures,luminescence characteristics,thermal stability and luminescence lifetime.Transient fluorescence spectroscopy data show that the addition of Bi³⁺ can obviously enha...     

Rare earth double activated phosphors for different applications

For the purpose of development of highly energy-efficient light sources, one needs to design highly efficient green, red and yellow phosphors, which are able to absorb excitation energy and generate emissions. In this contribution, we present our results on producing some efficient phosphors with improved luminescence properties. Using double activation, energy could be transferred from one luminescent activator to the other one, resulting in more efficient or brighter device operation. Co-activators could be added to a host material to change the color of the emitted light. The incorporation of Eu³⁺ or Tb³⁺ ions into the CaWO₄ crystal lattice modified the luminescence spectrum due to the formation of the emission centers that generated the specific red and green light. Very efficient new red phosphors based on YNbO₄ and doped by Eu³⁺, Ga³⁺, Al³⁺ allowed recommending these materials as good candidates for different applications including LED and X-ray intensifying screens. For double activated TAG with Ce³⁺ and Eu³⁺ and for different mole ratios of Ce/Eu, the color temperature changed from 5500 K (0.331, 0.322) up to 4200 K (0.370, 0.381) and the light became “warmer”. Application of TAG: Ce, Eu in the light emitting device showed better chromaticity coordinates of luminescence and color rendering index of LEDs.     

Energy transfer and luminescent properties of Pr^3＋ and/or Dy^3＋ doped NaYF4 and NaGdF4

The phosphors that are able to convert vacuum ultraviolet（VUV） light into visible light are demanded for the development of novel displaying and lighting devices.NaYF4：Pr3＋,Dy3＋,NaGdF4：Pr3＋,NaGdF4：Dy3＋and NaGdF4：Pr3＋,Dy3＋were prepared by hydrothermal synthesis method and their luminescent properties in VUV-vis spectral region were investigated at room temperature.For NaYF4：Pr3＋,Dy3＋,no energy transfer process from Pr3＋to Dy3＋was observed.However,the introduction of Gd3＋into the fluoride lattice led to intense Dy3＋emissions upon Pr3＋4f5d state excitation.Gd3＋acted as an intermediate,resulting in efficient energy transfer from Pr3＋to Dy3＋in NaGdF4.Pr3＋transferred most of its energy to Gd3＋,and then the energy was transferred from Gd3＋to Dy3＋.So NaGdF4：Pr3＋,Dy3＋not only took full advantage of the intense Pr3＋4f5d absorption,but converted the VUV excitation light into the near-white emission of Dy3＋.     

Synthesis and luminescent properties of low oxygen contained Eu^2＋-doped Ca-α-SiAION phosphor from calcium cyanamide reduction

A new convenient calcium cyanamide （CaCN2） reduction route was developed to synthesize the Eu^2＋ activated Ca-α-SiAION phosphors containing low oxygen content. The luminescence properties of the obtained products were investigated for white LEDs application. The critical Eu^2＋ concentration in various hosts and its effect on the photoluminescence properties were studied. The optimized sample （10at.% Eu^2＋ vs. Ca^2＋） could be efficiently excited by the current GaN/InGaN blue LED chips and provided emission intensity competitive with that of YAG：Ce^3＋ （P46-Y3） standard, revealing that this phosphor was a potential candidate for phosphor-converted white LEDs.     

Novel phosphors of Eu^3＋, Tb^3＋ or Tm^3＋ activated LaBGeO5

Rare earth borogermanates as a group of stable compounds provided various potential properties important for modern sciences. Among the properties of interests, luminescence was manifested due to the variability of rare earth elements and the compounds constituted an important group of potential candidate. In this work, novel phosphors of Eu³⁺, Tb³⁺ or Tm³⁺ doped LaBGeO₅ with the stillwellite type structure were synthesized by the solid state reaction method. Their X-ray and UV excitation luminescent properties showed that LaBGeO₅ was an excellent host lattice for the luminescence of Eu³⁺, Tb³⁺ and Tm³⁺. The LaBGeO₅:Eu³⁺, LaBGeO₅:Tb³⁺ and LaBGeO₅:Tm³⁺ presented bright red, green and blue emission light for both UV and X-ray excitation.     

Fabrication and photoluminescence characteristics of novel red-emitting Ba2LuNbO6:Eu3+ double-perovskite phosphors on near UV WLEDs

Red emitting phosphors play a significant role in accelerating the improvement of illumination quality for white light emitting diodes (WLEDs). In this work, by using solid-state reaction method, an efficient novel Ba₂LuNbO₆:Eu³⁺ phosphor with double-perovskite structure was successfully prepared. Here, a series of Ba₂LuNbO₆:Eu³⁺ red phosphors can be efficiently pumped by the near-ultraviolet (UV) light and then present high-brightness at orange emission (598 nm, ⁵D₀→⁷F₁) and red emission (610 nm, ⁵D₀→⁷F₂). The ratio values of 610 to 598 nm in Ba₂LuNbO₆:Eu³⁺ phosphors exceed 1 when the content of Eu³⁺ is larger than 0.4 mol, because the occupation of Eu³⁺ ions is changed from Lu³⁺ ions with symmetric sites to Ba²⁺ ions with asymmetric sites. Besides, the optimized concentration of Eu³⁺ at the ⁵D₀→⁷F₂ transitions is obtained when x = 1, indicating that there is non-concentration quenching in Ba₂LuNbO₆:Eu³⁺ phosphors. Moreover, the CIE chromaticity coordinates of Ba₂LuNbO₆:Eu³⁺ was calculated to be (0.587, 0.361), the color purity was calculated to be 72.26% and internal quenching efficiency (IQE) was measured to be 67%. Finally, the thermal stability of Ba₂LuNbO₆:Eu³⁺ phosphors was also studied. Our work demonstrates that the novel double-perovskite red-emitting Ba₂LuNbO₆:Eu³⁺ phosphors are prospective red emitting elements for WLEDs applications.     

Luminescent properties of Eu~（3＋） doped Gd_2WO_6 and Gd_2（WO_4）_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in different matrixes were studied. The results indicated that effective Eu3+:5D0-7F2 red luminescence could be achieved while excited by 395 nm near-UV light and 465 nm blue light in Gd2WO6 host, which was similar to the familiar Gd2(WO4)3:Eu. Therefore, the Gd2WO6:Eu red phosphors might have a potential application for white LED.     

Luminescence properties of red phosphors Ca_（10）Li（PO_4）_7：Eu~（3＋）

A series of red phosphors Ca10Li (PO4)7:Eu3+ were synthesized by high temperature solid-state reaction method. Their luminescence properties were characterized by means of photoluminescence excitation and emission spectra,CIE chromaticity and quantum efficiency. Results indicated that the phosphors could be effectively excited by the near ultraviolet (NUV) light (393 nm). The main emission peaks of the phosphor were ascribed to the transition 5D0-7F2 (613 and 617 nm) of Eu3+ ion when samples were excited by...     

Broadband downconversion in YVO4：Tm3＋,Yb3＋ phosphors

An efficient near-infrared (NIR) downconversion (DC) by converting broadband ultraviolet (UV) into NIR was demonstrated in YVO4:Tm3+,Yb3+ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffraction, photoluminescence excitation, photoluminescence spectra and decay lifetime to provide supporting evidence for DC process. Upon UV light varying from 260 to 350 nm or blue light (473 nm) excitation, an intense NIR emission of Yb3+ corresponding to transition of 2F5/2→2F7/2 peaking at 985 nm was generated. The visible emission, the NIR mission and the decay lifetime of the phosphors of various Yb3+ concentrations were investigated. Experimental results showed that the energy transfer from vanadate group to Yb3+ via Tm3+ was very efficient. Application of the broadband DC YVO4:Tm3+,Yb3+ phosphors might greatly enhance response of siliconbased solar cells.