Design of a narrow-band blue-emitting Rb2Ba3(P2O7)2:Eu2+ phosphor with low thermal quenching for plant growth LEDs

Phosphor-converted light-emitting diodes (pc-LEDs) are commonly used to regulate the light environment to control the growth rates and improve the production efficiency of plant. Among them, the exploration of blue-emitting phosphors with high efficiency, low thermal quenching and excellent spectrum resemblance matching with the plant response spectrum is still challenging. Herein, a narrow-band blue-emitting Rb₂Ba₃(P₂O₇)₂:Eu²⁺ phosphor with high color purity of 93.4% has been developed. Under 345 nm excitation, it exhibits a blue emission band centered at 413 nm with a full width at half-maximum (FWHM) of 36 nm, and the emission spectrum of Rb₂Ba₃(P₂O₇)₂:0.060Eu²⁺ sample shows 85.7% spectrum resemblance with the absorption spectrum of chlorophyll-a in the blue region from 400 to 500 nm. In addition, the temperature-dependent emission spectra demonstrate that the Rb₂Ba₃(P₂O₇)₂:0.060Eu²⁺ phosphor has good thermal stability and small chromaticity shift, with the emission intensity dropping to 72.5% at 423 K of the initial intensity at 298 K and a chromaticity shift of 38 × 10^-3 at 498 K. All results suggest that the blue-emitting Rb₂Ba₃(P₂O₇)₂:Eu²⁺ phosphor has potential application in plant growth LEDs.     

A novel pale-yellow Ba2ZnGe2O7:Bi3+ phosphor with site-selected excitation and small thermal quenching

A novel pale-yellow Ba₂ZnGe₂O₇:Bi³⁺ phosphor with site-selected excitation and small thermal quenching was synthesized by conventional solid-state sintering. The crystal structure and luminescence properties have been investigated in detail for the first time using XRD patterns, photoluminescence spectra, diffuse reflection spectra, decay curves, and temperature-dependent emission spectra. The results reveal that the excitation spectrum of Ba₂ZnGe₂O₇:Bi³⁺ phosphor locates in the near-ultraviolet region of 300-400 nm, and its emission shows an obvious site-selective excitation phenomenon since Bi³⁺ ions occupy two different crystallographic sites in the Ba₂ZnGe₂O₇ host. When excited under 360 nm, the phosphors show a pale-yellow emission in the range of 400-700 nm with the maximum peaking at 520 nm, while when excited under 316 nm, the phosphors show a blue emission in the range of 400-700 nm with the maximum peaking at 480 nm. In addition, the emission of Ba₂ZnGe₂O₇:Bi³⁺ can also be easily controlled by changing the Bi³⁺ concentration. The Ba₂ZnGe₂O₇:Bi³⁺ phosphor has small thermal quenching, and its emission intensity only decreases by 2% at 200°C. The results indicate that this novel pale-yellow Ba₂ZnGe₂O₇:Bi³⁺ phosphor could be conducive to the development of white light-emitting diodes.     

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).     

A novel red-emitting Na5W3O9F5:Eu3+ phosphor with high color purity for blue-based WLEDs

Red phosphor plays a key role in improving the lighting and display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). Meanwhile, developing new luminescent matrix materials can positively contribute to the acquisition of ideal and efficient phosphors. In this work, we propose a novel red-emitting Na₅W₃O₉F₅:Eu³⁺ (NWOF:Eu³⁺) phosphor. The phase composition, morphology, electronic structure and photoluminescence properties of the NWOF:Eu³⁺ phosphor were systematically investigated. The EXAFS results prove that the Eu³⁺ dopants occupy the Na2 and Na3 sites in the NWOF host. Under 466 nm blue light excitation, NWOF:xEu³⁺ (0.05 ≤ x ≤ 0.25) phosphors display a dominant red emission at 607 nm and achieves a high color purity (97.44%) due to the dominant electric dipole transition (⁵D₀→⁷F₂) of Eu³⁺ ions. Impressively, this red-emitting NWOF:0.25Eu³⁺ phosphor exhibits relatively superior thermal stability (450 K, >50%) and excellent chromaticity stability (2.32 × 10^?4 ≤ ΔE ≤ 6.23 × 10^?3) from 298 K to 498 K. The activation energy for thermal quenching effect is determined to be 0.22 eV. Moreover, the pc-WLED was fabricated by coupling a 460 nm blue chip with the as-synthesized NWOF:0.25Eu³⁺ red phosphor and commercial YAG:Ce³⁺ phosphor. The optical parameters of the as-fabricated pc-WLED are also measured, and the CIE coordinates remain almost constant as the drive current increases from 20 mA to 120 mA. These results indicate that the NWOF:0.25Eu³⁺ red phosphors should be a suitable candidate as a red component for the preparation of pc-WLEDs.     

A low cost and high efficient Ba9(Lu2-x-yAlx)Si6O24:yCe3+ cyan-emitting phosphor

White LEDs constructed by near-ultraviolet chips and red/green/blue/cyan-emitting phosphors are an important route for healthy lighting. However, efficient cyan-emitting phosphors are quite scarcity. The cyan-emitting phosphor Ba₉Lu_1.5Al_0.5Si₆O₂₄:Ce³⁺ (BLASO:Ce³⁺) was reported for the first time. Under 400 nm excitation, BLASO:Ce³⁺ shows a emission peak at 488 nm with an FWHM of about 117 nm. At room temperature, the internal quantum efficiency (IQE) can reach as high as 90.8%. At 150 °C, the IQE decreases to 81.5%, indicating an excellent thermal stability. The effect of the Al substitution for Lu on crystal structures and photoluminescence were investigated. The homogeneity of the luminescence was diagnosed by viewing microscopic particles based on the scanning electron microscope (SEM) equipped a cathodoluminescence (CL) system.     

Novel cyan-emitting KBaScSi2O7:Eu2+ phosphors with ultrahigh quantum efficiency and excellent thermal stability for WLEDs

Owing to the conventional phosphor-converted white LEDs (pc-WLEDs) generally suffer from blue-green cavity, thus, developing an appropriate phosphors covering both the blue and green regions in their emission spectra are very urgent. Herein, a novel Sc silicate phosphor, KBaScSi₂O₇:Eu²⁺ (KBSS:Eu²⁺), has been successfully designed and prepared via a solid-state reaction. The crystal structure, luminescent properties, thermal quenching, quantum efficiency as well as its application in UV-pumped WLEDs have been investigated systematically. The KBSS:Eu²⁺ phosphor exhibits a strong and broad excitation band ranging from 290 to 450 nm, and gives a sufficient cyan emission of 488 nm with a full-width half-maximum (FWHM) of 70 nm, which filled the blue-green cavity. Importantly, the optimized KBSS:Eu²⁺ phosphor possesses an ultrahigh quantum efficiency (QE) up to 91.3% and an excellent thermal stability retaining 90% at 423 K with respect to that measured at room temperature. Finally, the as-fabricated UV-based WLEDs device, with only coupled the mixture of KBSS:Eu²⁺ cyan phosphor and CaAlSiN₃:Eu²⁺ red ones to a commercial 365nm UV chip, exhibits a satisfactory color-rendering index (Ra = 88.6), correlated color temperature (CCT = 3770K), and luminous efficiency (LE = 21 lm/W).     

Insight into a concentration-sensitive red-emitting phosphor Li2Ca4Si4O13:Eu3+ for multifunctional applications: Crystal structure,electronic structure and luminescent properties

Lithium-containing silicate compounds have attracted so much attention in recent years for applications in energy storage and illumination source due to their rigid structure and good electrical conductivity. In this study, a Eu³⁺ doped lithium-containing silicate red phosphor, Li₂Ca₄Si₄O₁₃:Eu³⁺, was explored by using structural computational simulations and systematic experiments for multifunctional applications. As a result, due to the quite non-central symmetry of the Ca²⁺ sites (C₁ symmetry), the strong 4f-4f excitations in near ultraviolet region were observed. Under near ultraviolet and cathode ray light excitation, Li₂Ca₄Si₄O₁₃:Eu³⁺ phosphor has an efficient red emission with good thermal stability and ageing resistance. Furthermore, Li₂Ca₄Si₄O₁₃:Eu³⁺ phosphor exhibits a concentration-sensitive behavior induced by the change of site symmetry. The results show that it is feasible to develop near-ultraviolet and cathode ray light excited red phosphors in lithium-containing silicate compounds.     

Eu2+, Dy3+: Sr2B5O9Cl,a new blue-emitting phosphor with long persistence

A new Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphor with long persistence was synthesized in a reducing atmosphere by a solid-state reaction process. The pure-phase phosphor was obtained by calcination at 900 °C. The introduction of Eu²⁺ into the lattice of the matrix resulted in a broad blue emission centered at 423 nm, which was due to the characteristic 4f6⁵d¹ to 4f⁷ energy transfer of Eu²⁺ ions. Both Eu-doped and Dy/Eu-codoped phosphors displayed afterglow behaviors due to the electron traps generated by the incorporation of tri-valanced rare earth cations into the original Sr lattice sites. The afterglow of Eu²⁺: Sr₂B₅O₉Cl and Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphors showed standard double exponential decay behaviors, and the Eu²⁺/Dy³⁺ co-doped sample demonstrated better afterglow properties than Eu²⁺-doped one. A longer lifetime for the electrons was confirmed after the afterglow decay curve simulation. Based on the analysis of thermally stimulated luminescence (TSL), the difference in afterglow was attributed to the different trap concentrations induced by the Dy³⁺ (Eu³⁺) doping in the Sr₂B₅O₉Cl matrix.     

Optical properties of the CaEuAl3O7 phosphor with dual-activator Eu2+/Eu3+ for multifunctional applications

At present, most blue-red composite LED light sources are widely used in the field of plant lighting. However, their full-width at half-maximum of blue light is too small to meet the requirements of plants for photosynthesis. Herein, a dual-emitting single-phase self-luminescent phosphor CaEuAl₃O₇ (CEAO) is reported in this study, which provides broadband blue emission of Eu²⁺ ions and red emissions of Eu³⁺ ions. According to the optical properties of Eu²⁺ and Eu³⁺ ions in the CEAO phosphor, it can be found that all emissions are consistent with the absorption of chlorophylls and pigment carotenoids. In addition, the temperature sensing based on the fluorescence intensity ratio (FIR) in the CEAO phosphor is also studied and the maximum sensitivity (S) can reach as high as 6.90% K⁻¹ at 313 K. The results indicate that the single-component phosphor CEAO with blue and red double-color emission possesses an outstanding potential in plant growth lamps and optical thermometry applications.     

Tunable chromaticity and high color rendering index of WLEDs with CaAlSiN3:Eu2+ and YAG:Ce3+ dual phosphor-in-silica-glass

Phosphors-in-glass (PiG), which serves as a potential bi-replacement of both phosphors and organic encapsulants in high-power white light-emitting diodes (WLEDs), has captured much attention due to its high thermal stability and excellent luminescent properties. However, due to the high-temperature sensitivity and the chemical reactions between phosphors with glass matrix, a variety of phosphors, especially red phosphors could be hardly dispersed into the glass without thermal quenching and decomposition, which greatly limits the improvement of color rendering index and chromaticity tunability of the WLEDs. In this study, adopting the mesoporous silica (FDU-12) and commercial phosphors as raw materials, the phosphors-in-silica-glasses (PiSGs) embedded with red phosphor CaAlSiN₃:Eu²⁺ and yellow phosphor YAG:Ce³⁺ have been successfully prepared at low sintering temperature (950°C) and short preparation time (10 minutes) using spark plasma sintering. Owing to the well preservation of the originally emissive properties of the embedded phosphors, the warm WLEDs with tunable chromaticity and exhibited a superior performance with LE of 133 lm/W, CCT of 3970 K and CRI of 81 were fabricated by encapsulating the as-prepared PiSGs on the blue chips. Moreover, the PiSG composite exhibits a high thermal conductivity up to 1.6 W/m·K.     

Synthesis and photoluminescence of novel blue-emitting phosphor of Eu2+-activated fluoroborate BaGaBO3F2

Pure and Eu²⁺-activated fluoroborate BaGaBO₃F₂ was prepared using high-temperature solid-state reaction. BaGaBO₃F₂ is a wide band semiconductor with the indirect transition characteristic. The excitation and luminescence spectra of the phosphor were measured, and it was found that Eu²⁺-activated BaGaBO₃F₂ exhibits a bright blue color under ultraviolet (UV) light. The narrow emission band peaked at 425 nm is attributed to the transitions of 4f⁶5d→4f⁷(⁸S_7/2), and the Stokes shift estimated for this phosphor sample is 3140 cm⁻¹. The lifetime of the luminescence is also reported. The absolute quantum efficiency (QE) of the phosphor was evaluated, and it was found that the absolute QE decreases with increasing Eu²⁺ concentration. The phosphor shows an excellent quantum efficiency of 72.5% and a high thermal activation energy of 0.342 eV. The study concludes that Eu²⁺-doped BaGaBO₃F₂ phosphor has promising luminescence application abilities and can be used as a blue-emitting phosphor in a variety of applications.     

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 co-precipitation synthesis of a new phosphor Lu2O3:Eu3+

Europium-doped Lu₂O₃ phosphors were prepared via a co-precipitation process. The influence of precipitants on morphology and dispersibility of the obtained Lu₂O₃ powders were investigated. Precipitation was performed with three different precipitants, namely ammonium hydroxide (NH₃·H₂O), ammonium hydrogen carbonate (NH₄HCO₃), and the mixture of NH₃·H₂O and NH₄HCO₃. Ultrafine, nearly monodispersed, weakly agglomerated and near-spherical lutetia powders could be obtained with mixed NH₃·H₂O and NH₄HCO₃ as the precipitant. The precipitate precursor with the mixed precipitant was believed to possess a basic carbonate composition and its thermal decomposition and phase evolution processes were investigated. Photoluminescence characteristics of Lu₂O₃:Eu³⁺ phosphors obtained by this modified precipitation method were also studied.     

白光LED用红色荧光粉的制备及发光性能

采用溶胶凝胶法(sol-gel)合成CaO-MgO-S iO2:Eu3+荧光粉,在近紫外393nm激发下发射出Eu3+的特征红色光谱,并研究了该方法中各种工艺条件(如:pH值,Eu3+的掺杂量等)对其影响。通过X射线粉末衍射、荧光光谱等分析其发光特性,表明Eu3+离子在CaO-MgO-S iO2:Eu3+基质中处于较低的对称格位,发射来源于5D0→7F2613nm为主的红光。     

自蔓延燃烧法制备Ba3MgSi2O8∶Eu2+,Mn2+荧光粉

本文以乙二醇为溶剂,无水乙醇为助燃剂,首次采用自蔓延燃烧法制备了白光LED用Ba3Mgsi2O8∶Eu2+,Mn2+荧光粉,利用XRD、粒度分析仪和荧光分光光度计对样品进行了测试,荧光分析结果表明:在375nm波长光源激发下,1100℃制备的样品可同时发射绿、蓝两色光.     

A novel Li2CaSi2N4:Eu2+ orange-red phosphor for field-emission displays

The exploration of suitable phosphors with high efficiency, low saturation, and good stability has always been a key issue for field-emission displays (FEDs) development. In this work, a novel Li₂CaSi₂N₄:Eu²⁺ orange-red phosphors were prepared by solid reaction process and the cathodoluminescence (CL) properties were investigated in detail to explore the potential application for FEDs. Under a low voltage electron-beam excitation, the phosphors show an intense orange-yellow emission in the range of 500-700 nm, which belongs to the 4f⁶5d→4f⁷ electron transition of Eu²⁺ ion. The influences of the Eu²⁺ doping concentration, filament current, accelerating voltage, and bombardment time on the CL emission of Li₂CaSi₂N₄:Eu²⁺ were investigated in detail. The results indicate that Li₂CaSi₂N₄:Eu²⁺ phosphors exhibit an intense orange-red emission, no saturation effect, and excellent degradation property, which give the Li₂CaSi₂N₄:Eu²⁺ phosphors potential application in full color FEDs.     

Photoluminescence properties of NUV light excited Ba(Mg1/3Nb2/3)O3:Eu3+ red phosphor with high color purity

In this work, a new red phosphor with high color purity, Eu³⁺ ions doped Ba(Mg_1/3Nb_2/3)O₃ phosphor has been prepared by wet chemical method. The structure analysis suggests BMN:x%Eu phosphors have a hexagonal phase and Ba²⁺ ions are replaced by Eu³⁺ ions in BMN. Upon excitation of NUV light, the BMN:x%Eu phosphors emit strong red light around 615?nm, derived from the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The relationship between luminescent properties and structure of BMN:x%Eu was discussed. The Judd-Ofelt intensity parameters (Ω₂, Ω₄) were calculated to analyze the asymmetry of the Eu³⁺ ions site occupancy further, and the quantum efficiency of BMN:3%Eu was found to be 77.26%. In addition, the decay curve indicates the decay time(τ) of BMN:3%Eu is determined to be 1.34?ms and Eu³⁺ ions occupy only one type of site. The CIE chromaticity coordinate (0.656,0.344) of BMN:3%Eu is quite close to the red phosphors standard value (0.670, 0.330), which indicates BMN:x%Eu can be a suitable red phosphor used in NUV-based white LEDs.     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

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.     

Novel double-perovskite Mg2InSbO6:Sm3+ phosphor with excellent heat-resistant performance and high color purity used in white LEDs

In this study, Sm³⁺-doped double-perovskite Mg₂InSbO₆ phosphors were synthesized via high-temperature solid-state reaction. Mg₂InSbO₆ belongs to the double-perovskite family with a space group of R (No.148). The photoluminescence (PL) spectrum illustrates that Mg₂InSbO₆:0.05Sm³⁺ phosphor can emit intense orange-red emission light at 607 nm due to the ⁴G_5/2→⁶H_7/2 transition. The optimum concentration of Mg₂InSbO₆:xSm³⁺ is confirmed to 0.05 mol. The asymmetric ratio (⁴G_5/2→⁶H_9/2/⁴G_5/2→⁶H_5/2) of Mg₂InSbO₆:0.05Sm³⁺ phosphor is 2.73. The quenching temperature exceeds 500 K, illustrating that Mg₂InSbO₆:Sm³⁺ sample has excellent heat resistance. The high color purity and correlated color temperature (CCT) of Mg₂InSbO₆:Sm³⁺ phosphors are obtained. Furthermore, a white light-emitting diode (w-LED) is successfully fabricated, possessing CCT of 6769 K and high color rendering index (R_a) of 89. Therefore, the orange-red-emitting Mg₂InSbO₆:Sm³⁺ phosphors exhibit great potential to apply in solid-state lighting fields.