Enhanced thermal stability of CaAlSiN3:Eu2+ phosphors by superficial carbon modification

To satisfy increasing stringent application requirements for high power wLEDs, we propose a superficial carbon modification method to enhance thermal stability of red-emitting CaAlSiN₃:Eu²⁺ phosphor via carbon coating by mechanical mixing and thermal post-treatment at high temperature under N₂-H₂ atmosphere. The modifications on the crystal surface include (a) elimination of amorphous phase, (b) introduction of carbon and (c) inhibition of the oxidation of Eu²⁺. During the whole processing, the route of carbon and its effects on the crystal structure and luminescence properties are investigated by XPS, TEM, SEM, Raman spectra and TG-DSC analysis. After superficial carbon modification, the thermal quenching characteristic is improved by 5.7%, and the relative brightness decays more slowly during the aging test, which means that the superficial carbon modified samples still maintain good luminescence performance at high temperature and have superior performance for long-term applications. All above indicate that the superficial carbon modification method is a promising application to enhance the thermal stability for analogous Eu²⁺-activated nitride phosphors.     

Enhanced thermal quenching characteristic via carbon doping in red-emitting CaAlSiN3:Eu2+ phosphors

Enhancing thermal quenching characteristic of phosphor for use in high power white-light-emitting diodes (wLEDs) is a significant materials challenge. To achieve this goal, a series of red-emitting carbidonitride phosphors Ca_0.992AlSiN_3 − 4/3xC_x:0.008Eu²⁺ have been synthesized by high-temperature solid-state reaction method. Crystal structure, luminescence properties, and thermal quenching process are investigated. The location of carbon in the lattice is proved by the Raman spectra. The preferential crystallographic site of carbon is validated by the first-principles density functional theory calculations combining the Rietveld refinement. With carbon doping from x = 0 to x = 0.24, the emission spectra are blue-shifted from 656.8 to 650.2 nm, and the fitted lifetime of Eu²⁺ decreases from 775.3 to 721.7 ns. Replacing nitrogen by carbon enhances thermal quenching characteristic by 8.9% at 300°C. Carbon doping enlarges the thermal ionization energy barriers (E_dC) which is calculated at great length, and suppresses thermal ionization process. A wLED fabricated by the combination of a blue chip with the as-synthesized red phosphor and LuAG: Ce³⁺ green phosphor shows a high color rendering indexes (Ra = 95.9 and R9 = 92). The promising application of Ca_0.992AlSiN_3 − 4/3xC_x:0.008Eu²⁺ phosphor for wLEDs is proved by all results above.     

A novel scheelite-type LiCaGd(WO4)3:Eu3+ red phosphors with prominent thermal stability and high quantum efficiency

A series of LiCaGd(WO4)3 : xEu³⁺ (0 ≤ x ≤ 1.0) red phosphors with tetragonal scheelite structure were synthesized via the conventional solid-state reaction. Their crystal structure, photoluminescence excitation (PLE), and photoluminescence (PL) spectra, thermal stability and quantum efficiency were investigated. The phosphors exhibit a typical red light upon 395 nm near ultraviolet excitation, and the strongest emission peak at 617 nm is dominated by the ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The PL intensity of the phosphors gradually increases with the increase of Eu³⁺ doping concentration, and the concentration quenching phenomenon is hardly observed. The quantum efficiency and the color purity of the phosphor reach maximum values of about 94.2 and 96.6% at x = 1.0, respectively. More importantly, LiCaGd(WO₄)₃:xEu³⁺ phosphors have prominent thermal stability. The temperature-dependent PL intensity of the phosphors at 423 K is only reduced to 89.1% of the PL intensity at 303 K, which is superior to that of commercial red phosphors Y₂O₃:Eu³⁺. Finally, LiCaGd(WO₄)₃:Eu³⁺ phosphor is packaged with near ultraviolet InGaN chips to fabricate white light emitting diodes, which has a low color temperature (CCT = 4622 K) and a high color rendering index (CRI= 89.6).     

Enhancing emission intensity and thermal stability by charge compensation in Sr2Mg3P4O15:Eu3+

Charge compensation was the effective methods to enhance the luminescence properties of phosphors. In this paper, novel single‐phased orange light emitting Sr₂Mg₃P₄O₁₅:Eu³⁺ phosphors were prepared by solid state method. The phase purity and luminous characteristics were examined in detail. Meanwhile, three kinds of charge compensation methods (co‐doping the alkali metal R⁺ (R⁺ = Li, Na, and K), substituting Si⁴⁺ for P⁵⁺ and self‐compensation) were employed to solve the charge imbalance problem between Sr²⁺ and Eu³⁺. The results showed that emission intensity of Eu³⁺ was improved by 1.43 (Li⁺), 1.58 (Na⁺), 1.53 (K⁺), 1.61 (Si⁴⁺), and 1.30 (self) times than that of Sr_1.6Mg₃P₄O₁₅:0.40Eu³⁺, respectively, and there was no change in the emitting color simultaneously. Furthermore, as the temperature reached at 423 K, the emission intensity increased from 41.67% of Sr_1.6Mg₃P₄O₁₅:0.40Eu³⁺ to 55.69% (Li⁺), 61.62% (Na⁺), 58.98% (K⁺), 71.15% (Si⁴⁺), and 80.59% (self) of that at room temperature. The reasons of those phenomena were the reduction in ion vacancies caused by charge imbalance through the charge compensation process. The specific mechanisms were elaborated in detail. Overall, this research validated that the charge compensation strategies could be severed as the key method to improve the luminescence properties, especially the thermal stability of phosphor.     

Improving the luminescence properties and powder morphologies of red-emitting Sr0.8Ca0.19AlSiN3:0.01Eu2+ phosphors for high CRIs white LEDs by adding fluxes

Red-emitting Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ phosphor with halide fluxes for use in the production of white light-emitting diodes (white LEDs) with high-colour rendering indices (CRIs) was prepared through the high-temperature solid-state method. Fluoride (NaF, SrF₂, BaF₂, CaF₂, AlF₃·3H₂O and CeF₃), chloride (NH₄Cl, BaCl₂, MgCl₂, NaCl and LiCl) and composite fluxes (NaF + SrF₂, SrF₂+NH₄Cl and NaF + NH₄Cl) were applied in the phosphors. NaF, SrF₂, NH₄Cl and NaF + SrF₂ fluxes had prominent effects on the characteristics of Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ phosphors. Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ phosphors with various powder morphologies can be obtained through the addition of fluxes, which are conducive for phosphor formation. The powder morphologies of phosphors incorporated with NaF + SrF₂ were preferable to those of powders incorporated with other fluxes. This result indicated that the incorporation of NaF + SrF₂ into Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ yielded phosphors with high luminescent intensity and quantum efficiency, excellent thermal stability, narrow full widths at half-maximum (FWHM, 75.2 nm), uniform rod-like morphologies with large particle sizes (D₅₀ = 16.99 μm) and good particle dispersion. White LEDs with high CRIs were obtained by combining prepared phosphors (NaF + SrF₂ additive) with the commercial green-emitting phosphors Y₃(Al,Ga)₅O₁₂:Ce³⁺ and (Sr,Ba)₂SiO₄:Eu²⁺. White LEDs with Y₃(Al,Ga)₅O₁₂:Ce³⁺ and (Sr,Ba)₂SiO₄:Eu²⁺ phosphors had correlated colour temperatures (CCTs) of 3064 and 3023 K, respectively, and CRIs of 81.8 and 92.4, respectively. Therefore, NaF + SrF₂ can be used as a favourable flux for the production of Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺.     

Enhanced red emission and improved thermal quenching of CaAlSiN3:Eu2+ phosphors via boron doping

The development of high-performance phosphors is required for phosphor-converted white light-emitting diodes. However, most approaches are unable to achieve optimum emission intensity and thermal quenching simultaneously. Here, a series of CaAlSiN₃:Eu²⁺ (CASN:Eu²⁺) red-emitting phosphors doped with B were synthesized using field-assisted sintering technology. Compared with CASN:Eu²⁺, the B-doped phosphor exhibited high external quantum efficiency (EQE) and good thermal quenching performance. With boron doping, the EQE of CaAlSiN₃:Eu²⁺ shows an obvious growth, increasing from 48.83% to 70.68%. Meanwhile, thermal quenching performance has also been greatly improved, which is strongly associated with the band structure of Eu²⁺ and the crystal structure of CASN. The location of B in the crystal lattice was studied and the mechanism of improving thermal quenching via B doping was discussed in detail. Finally, a white LED fabricated by the combination of a GaN blue chip (450 nm) with the as-synthesized red phosphors and Y₃(Al, Ga)₅O₁₂:Ce³⁺ green phosphors (531 nm), shows a high color rendering index (Ra =91.6). This study offers a novel method to improve luminescence properties of CASN:Eu²⁺ red-emitting phosphors, which may broaden their application in solid-state lighting devices.     

Luminescent properties of Na2GdMg2(VO4)3:Eu3+ red phosphors for NUV excited pc-WLEDs

Herein, a series of novel Na₂GdMg₂(VO₄)₃:Eu³⁺ (NGMVO:Eu³⁺) red phosphors were elaborated by conventional solid-state reaction process. Their structural features, luminescent properties, energy transfer were researched at length. XRD patterns indicate that NGMVO:Eu³⁺ crystallized in single cubic garnet structure. Under the excitation of near ultraviolet light at 356 nm, the emission spectra of NGMVO host could be divided in two parts that resulted from ³T₂ → ¹A₁ and ³T₁ → ¹A₁ transitions of VO₄^3?. While NGMVO:Eu³⁺ phosphors show intense sharp red emission peaks including 590, 610, 652 and 706 nm that originated from ⁵D₀ → ⁷F_J (J = 1–4) transitions of Eu³⁺, respectively. The optimal concentration of Eu³⁺ is 0.7. Importantly, NGMVO:0.7Eu³⁺ sample presents high energy transfer efficiency (89 %) and high external quantum efficiency (48.3 %). Besides, its emission intensity remains 79 % at 420 K compared with that at 300 K, proving the good thermal stability of phosphors. All above results suggest that NGMVO:Eu³⁺ red phosphors have latent applications in white light emitting diodes.     

Luminescence properties of Ca2GdNbO6: Sm3+, Eu3+ red phosphors with high quantum yield and excellent thermal stability for WLEDs

A series of Ca₂GdNbO₆: xSm³⁺ (0.01 ≤ x ≤ 0.15) and Ca₂GdNbO₆: 0.03Sm³⁺, yEu³⁺ (0.05 ≤ y ≤ 0.3) phosphors were synthesized by the traditional solid-state sintering process. XRD and the corresponding refinement results indicate that both Sm³⁺ and Eu³⁺ ions are doped successfully into the lattice of Ca₂GdNbO₆. The micro-morphology shows that the elements of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor are evenly distributed in the sample, and the particle size is about 2 μm. The optical properties and fluorescence lifetime of Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors were detailedly studied. The emission peak at ⁵D₀→⁷F₂ (614 nm) is the strongest and emits red light under 406 nm excitation. The increase of Eu³⁺ concentration causes the energy transfers from Sm³⁺ to Eu³⁺ ions, and the transfer efficiency reaches 28.6%. Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor has a quantum yield of about 82.7%, and thermal quenching activation energy is of 0.312 eV. The color coordinate (0.646, 0.352) of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphors is located in the red area. The LED device fabricated based on the above phosphor emit bright white light, and CCT = 5400 K, Ra = 92.8. The results present that Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors potentially find use in the future.     

A far-red-emitting (Gd,Y)3(Ga,Al)5O12:Mn2+ ceramic phosphor with enhanced thermal stability for plant cultivation

As for plants, far-red (FR) light with wavelength from 700 nm to 740 nm is critical for processes of photosynthesis and photomorphogenesis. Light-controlled development depends on light to control cell differentiation, structural and functional changes, and finally converge into the formation of tissues and organs. Phosphor converted FR emission under LED excitation is a cost-effective and high-efficient way to provide artificial FR light source. With the aim to develop an efficient FR phosphor that can promote the plant growth, a series of gadolinium yttrium gallium garnet (GYGAG) transparent ceramic phosphors co-doped with Mn²⁺ and Si⁴⁺ have been fabricated via chemical co-precipitation method, followed sintered in O₂ and hot isostatic pressing in this work. Under UV excitation, the phosphor exhibited two bright and broadband red emission spectra due to Mn²⁺: ⁴T₁ → ⁶A₁ spin-forbidden transition, and one of which located in the right FR region. And then, Ce³⁺ ions were co-doped as the activator to enhance the absorption at blue light region and the emission of Mn²⁺. It turns out that the emission band of GYGAG transparent ceramic phosphors matches well with the absorption band of phytochrome P_FR, which means they are promising to be applied in plant cultivation light-emitting diodes (LEDs) for modulating plant growth. Besides, the thermal stability of this material was investigated systematically, and an energy transferring model involves defects was also proposed to explain the phenomenon of abnormal temperature quenching.     

Coexistence mechanism of Eu2+/Eu3+ ions in YAl3(BO3)4: Crystal structure,luminescence property,and substitution defects

The coexistence mechanism of Eu²⁺ and Eu³⁺ ions in YAl₃(BO₃)₄ host under different reducing conditions is investigated and confirmed in great detail, which can be described by three aspects as following. First, Eu³⁺ is protected by the layered structure of YAl₃(BO₃)₄. Second, the number of the interstitial defects ((Al)_i^…,(Y)_i^…) increases with increasing Eu²⁺ to maintain the charge balance of the system. And these defects can capture free electrons which are used for the reduction of Eu³⁺. Finally, free holes become more and more with the number of nonequivalent substitution defects (Eu_Y') increasing, which make the 5d electrons of Eu²⁺easily escape to the conduction band and Eu²⁺ convert to Eu³⁺. This work will be of great significance to research coexistence of multiple valence ions in the structure of borate and defect motion with nonequivalent substitution.     

Eu2+ activated novel eulytite Na3Bi5(PO4)6: Eu3+ phosphors: Enhanced luminescence and thermal stability for photonics application

For the first time, novel eulytite-like Eu²⁺/Eu³⁺: Na₃Bi₅(PO₄)₆ phosphor was synthesized via high temperature solid-state reaction method in reduction environment, and the structure, luminescence performances and thermal stability were investigated and discussed using various techniques. X-ray refinement diffraction and Raman spectra revealed the around 200 nm well-crystallized eulytite-type (I43d space group) phosphors were synthesized, and a diagram of crystal structure of Na₃Bi₅(PO₄)₆ was proposed. X-ray photoelectron spectroscopy analysis confirmed the co-existence of Eu²⁺ and Eu³⁺ ions which exhibited characteristic 4f⁶5d→⁸S_7/2 transition of Eu²⁺ and ⁷F₀→⁵D_0,1,2,3,4 transitions of Eu³⁺ ions. On the other hand, due to the activation of Eu²⁺, samples displayed good tunability on excited and emission behaviors under different excited laser. The JO parameters, emission cross-section, branching ratio and asymmetric ratio indicated that the Eu doping increased the covalency and asymmetry of host. Thermal quenching was studied and the reasons were discussed. Through the comparison of phosphors prepared in different conditions, the thermal stability& repeatability, radiative lifetime, color purity and activation energy were remarkably superior due to the Eu doping and in particularly Eu²⁺ activation. Finally, the energy level and CIE chromaticity diagrams were plotted to explain the mechanism of Eu²⁺ activation and energy transfer between Eu²⁺ and Eu³⁺ ions. The 0.5%Eu doped Na₃Bi₅(PO₄)₆ exhibited promising tunable red-emission performance with quantum efficiency of 92%, activation energy of 0.24 eV, red color purity of 93.74% and very low non-radiative transfer ratio 44.20 s^?1 with smaller CCT (<2200 K).     

Cation vacancy repair towards a new yellow Ca7Sr3Na(PO4)7:Eu2+ phosphor

Cationic substitution is a prevalent strategy to tune the luminescence spectra of phosphors. In this work, we reported a series of Eu²⁺-activated whitlockite type Ca₇Sr_3.5-0.5xA_x(PO₄)₇ (CSPA; A =Li, Na, K) (x = 0–1.00) phosphors. The substitution by Na⁺ for both half occupied/vacant M(4) site was verified via Raman spectra, Reitveld refinement and HR-TEM, whereas a similar accommodation of K⁺ into the Ca₂Sr(PO₄)₂ (CSP) host cannot be realized due to the significant size mismatch. A continuous increase of Na⁺ contents led to the progressively structural contraction, promoting the migration of Eu²⁺ activator from looser M(4) to other sites, and regulating the luminescence behaviors. Consequently, the gradual red-shift of emission band terminated at a new yellow phosphor Ca₇Sr₃Na(PO₄)₇:0.04Eu²⁺. The cation vacancy repair developed in this work can not only migrate the Eu²⁺ activator among different cation sites, but also serves as a new strategy for tuning the luminescence properties of phosphor.     

Anti-thermal quenching of Eu3+ luminescence in negative thermal expansion Zr(WO4)2

Thermal quenching of luminescence is the most critical problem for rare earth doped phosphors used in light-emitting diodes (LEDs). Herein, we demonstrate that thermal quenching can be considerably suppressed via the negative thermal expansion effect in Zr(WO₄)₂ that serves as host for Eu³⁺ red emission. The photoluminescence (PL) intensity is surprisingly enhanced by 130% when the temperature is raised from room temperature to 100 °C. As temperature further increases to 160 °C, the PL intensity turns to reduce, which is still 1.4 times of that at room-temperature. Moreover, Zr(WO₄)₂:15%Eu phosphor has good durability, which still exhibits strong red luminescence (only 13% loss) after being kept in 85 °C/85% relative humidity chamber for 240 h. The anti-thermal quenching of Eu³⁺ luminescence can be ascribed mainly to the following two factors: first one is the thermal-enhanced energy transfer between Eu³⁺ ions induced by the contraction of Zr(WO₄)₂ unit-cell volume that leads to the strong structural rigidity of host lattice; second one would be electron traps in the host that favors the increase of electrons on the excited energy levels. This important anti-thermal quenching effect induced from the negative thermal expansion of the host matrix may stimulates a novel and efficient approach to design highly thermal stable phosphors for next-generation LEDs.     

Synthesis and luminescence enhancement of red-emitting Sr9Y(PO4)7:Eu3+ phosphor through Gd3+ co-doping for white light-emitting diodes

A series of Sr₉Y(PO₄)₇:Eu³⁺ and Sr₉Y(PO₄)₇:Eu³⁺, Gd³⁺ red-emitting phosphors were prepared via a high-temperature solid-state method, Gd³⁺ ion was co-doped in Sr₉Y(PO₄)₇:Eu³⁺ as sensitizer to enhance the luminescence property. The X-ray diffraction results verify that the structure of the as-prepared samples is consistent with the standard Sr₉Y(PO₄)₇ phase. All the Sr₉Y(PO₄)₇:Eu³⁺ samples show both characteristic emission peaks at 594 nm and 614 nm under near-ultraviolet excitation of 394 nm. The co-doping of Gd³⁺ significantly improves the luminescence intensity of the Sr₉Y(PO₄)₇:Eu³⁺ phosphors due to the crystal field environment effect and energy transfer of Gd³⁺→Eu³⁺ caused by the introduction of Gd³⁺, especially Sr₉Y(PO₄)₇:0.11Eu³⁺, 0.05Gd³⁺, which emission intensity is higher than that of Sr₉Y(PO₄)₇:0.11Eu³⁺ by 1.21 times. The color purity and lifetime of Sr₉Y(PO₄)₇:0.11Eu³⁺, 0.05Gd³⁺ phosphor are 88.26% and 3.7615 ms, respectively. A w-LED device was packaged via coating the as-prepared phosphor on n-UV chip of 395 nm with commercial phosphors. These results exhibit that the Sr₉Y(PO₄)₇:Eu³⁺, Gd³⁺ red-emitting phosphor can be used as a red component in the w-LEDs application.     

Li+掺杂浓度对Sr3ZnNb2O9:Eu3+荧光粉发光特性的影响

Li⁺作为电荷补偿剂可以提高Sr₃ZnNb₂O₉:Eu³⁺荧光粉的发光强度和热稳定性。本文通过高温固相反应成功制备了Sr₃ZnNb₂O₉:xEu³⁺,yLi⁺(0≤x≤0.5,0≤y≤0.5)荧光粉,为了鉴定和描述样品的物相、发光特性和热稳定性,进行了XRD和发光光谱测试。结果表明:Eu³⁺和Li⁺已经成功掺入到基质材料中,并取代Zn²⁺位点;Li⁺的最佳掺杂浓度为0.3(摩尔分数),浓度猝灭类型是在最近邻离子之间;掺杂Li⁺提高了荧光粉的热稳定性,活化能为0.193 eV,CIE色坐标为(0.651,0.349),非常接近国际照明委员会规定的标准色坐标。     

Effects of Eu3+ doping on the luminescence properties of novel Sr2CaLa(VO4)3 from partial substitution of Sr2+ by Ca2+ in Sr3La(VO4)3

Eu³⁺-activated Sr_3−xCa_xLa(VO₄)₃ phosphors were fabricated via citric-acid-assisted sol combustion. Characterization of the Sr_3−xCa_xLa(VO₄)₃:Eu³⁺ samples with different concentrations of Ca²⁺ revealed a hexagonal crystal structure belonging to the R-3m space group. The amount of Ca²⁺ added (x) was controlled within 0 ≤ x ≤ 2 to yield high-purity phosphors. Scanning electron microscopy results showed that an increase in Ca²⁺ concentration resulted in a decrease in the particle size of Sr_3−xCa_xLa(VO₄)₃:Eu³⁺, with the shape gradually changing from nearly equiaxed to lath-shaped. The Sr₂CaLa(VO₄)₃:Eu³⁺ phosphor (denoted as SCLVO:Eu³⁺) exhibited the strongest photoluminescence (PL) intensity at 618 nm among the samples under excitation of 394-nm near-UV (NUV) light. The study of Eu³⁺ doping concentration confirmed that Eu³⁺ could enter the lattice of the SCLVO matrix without altering its crystal structure. SCLVO:Eu³⁺ was found to strongly absorb 394 nm NUV light and 464 nm blue light. The optimal concentration of the Eu³⁺ dopant in the SCLVO host was 0.11, which resulted in the phosphor achieving an excellent PL intensity and a color purity of 98.68%. Tunable luminescence from the orange area (0.5280, 0.4522) of Commission Internationale de l'éclairage (CIE) to the red area (0.6313, 0.3650) was achieved by adjusting the concentration of Eu³⁺. Under 394 nm excitation, SCLVO:0.11Eu³⁺ phosphor has a quantum yield (QY) of 28.2% and excellent thermal stability with 0.383 eV activation energy. Consequently, White-light-emitting diode (WLED) based on SCLVO:0.11Eu³⁺ phosphor yielded a high color rendering index (CRI), low correlated color temperature (CCT), and CIE coordinates of 91.8, 5196 K, and (0.3407, 0.3612), respectively, under the 20 mA driven current. These results indicated the tremendous potential of SCLVO:0.11Eu³⁺ phosphors for application in WLEDs excited by NUV or blue light.     

Effect of A+ (A = Li,Na and K) co-doping on enhancing the luminescence of Ca5(PO4)2SiO4:Eu3+ red-emitting phosphors as charge compensator

A series of Ca_5-x(PO₄)₂SiO₄:xEu³⁺ red-emitting phosphors were synthesized through solid-state reaction, and alkali metal ions A⁺ (A = Li, Na and K) were co-doped in Ca₅(PO₄)₂SiO₄:Eu³⁺ to improve its luminescence property. The impacts of synthesis temperature, luminescence center Eu³⁺ concentration and charge compensator A⁺ on the structure and luminescence property of samples were studied in detail. X-ray diffraction results indicated that prepared Ca₅(PO₄)₂SiO₄:Eu³⁺, A⁺ had a standard Ca₅(PO₄)₂SiO₄ structure with space group P6₃/m. Under the excitation of 392 nm, Ca₅(PO₄)₂SiO₄:Eu³⁺ phosphors showed a red emission consisting of several emission peaks at 593 nm, 616 nm and 656 nm, relevant to ⁵D₀→⁷F₁, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄ electron transitions of Eu³⁺ ions, respectively. Luminescence intensity and lifetime of Ca₅(PO₄)₂SiO₄:Eu³⁺ can be significantly enhanced through co-doping alkali metal ion A⁺, which play an important role as charge compensator. The results suggest that Ca₅(PO₄)₂SiO₄:Eu³⁺, A⁺ red phosphors with excellent luminescence property are expectantly served as red component for white light-emitting diodes excited by near-ultraviolet.     

Ca0.7Sr0.3MoO4：Eu3+红色荧光粉发光性能的改进

采用水热法制备了 Ca0.70Sr0.18MoO4：Eu0.083+, Ca0.70Sr0.18?1.5xMoO4：Eu0.083+, Lax3+与 Ca0.70Sr0.18?yMoO4：Eu0.083+, La0.043+, Nay+红色荧光粉。用 X 射线衍射、扫描电子显微镜、荧光分光光度计对样品的物相、形貌以及发光性能进行测试和表征。结果表明：La3+离子的共掺杂可显著增强 Eu3+离子的发光性能。当 La3+的掺杂量为4％(摩尔分数)时,在395 nm 激发下,位于616 nm处的主发射峰的相对发光强度最大。另外,电荷补偿剂 Na+的引入,也明显增强了荧光粉的发光强度,荧光粉的最高发光强度是未引入 Na+荧光粉的1.47倍。     

Site-selective occupation and luminescence property investigation of Ca18Na3Y(PO4)14:Eu2+ phosphor for full-spectrum LED

Cyan-emitting phosphors have attracted widespread attention as an integral part to realize full-spectrum lighting. Understanding the site occupation of luminescence centers is of great importance to design and clarify the luminescent mechanism for new cyan-emitting phosphors. Here, we report a cyan-emitting phosphor Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ synthesized by the high-temperature solid-state method. The crystal structure is characterized by X-ray diffraction and refined by the Rietveld method. The diffuse reflectance spectra, excitation/emission spectra, fluorescence decay curves, thermal stability, and related mechanism are systematically studied. The results show that Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ crystallizes in a trigonal crystal system with space group R3c. Under excitation at 350 nm, a broadband cyan emission can be obtained at 500 nm with a half-width of about 120 nm, which is caused by Eu²⁺ occupying five different sites in host, namely, Na2O₁₂ (450 nm), (Ca3/Na1)O₈ (485 nm), Ca2O₈ (515 nm), Ca1O₇ (565 nm), and (Ca4/Y)O₆ (640 nm), respectively. Moreover, crystal structure, room and low temperature spectroscopy, and luminescence decay time are used to skillfully verify the site-selective occupation of Eu²⁺. Finally, a full-spectrum light-emitting diode (LED) lamp is fabricated with an improved color rendering index (∼90.3), CCT (∼5492 K), and CIE coordinates (0.332, 0.318). The results show that Ca₁₈Na₃Y(PO₄)₁₄:Eu²⁺ has the potential to act as a cyan emission phosphor for full-spectrum white LEDs.