Far-red-emitting YAl3(BO3)4:Cr3+ phosphors with excellent thermal stability and high luminescent yield for plant growth LEDs

Phosphors-converted LEDs (pc-LEDs) are excellent artificial light sources for indoor plant cultivation, in which the far-red-emitting component (700−780 nm) plays an important role in regulating the photomorphogenesis of plants. Accordingly, highly efficient and thermally stable far-red-emitting phosphors are indispensable for developing high-performance plant cultivation pc-LEDs. Herein, far-red-emitting YAl₃(BO₃)₄:Cr³⁺ (YAB:Cr³⁺) phosphors were synthesized by solid-state reaction, and their photoluminescence characteristics, thermal quenching, quantum yield (QY), and application in pc-LEDs were systematically investigated. The YAB:Cr³⁺ phosphor has an intense broadband absorption to the blue light, simultaneously exhibiting the sharp-line ²E emission and the broadband ⁴ T₂ emission of Cr³⁺ with a QY of ~86.7%. The far-red broadband emissions of YAB:Cr³⁺ centered at ~735 nm show a high resemblance to the active-state (P_FR) absorption of plant phytochrome. Moreover, the YAB:Cr³⁺ phosphor shows the thermally enhanced luminescence at temperatures of 303−393 K and the near-zero thermal quenching up to 423 K. The anomalous thermal enhancement is attributed to the temperature-dependent repopulation between ²E and ⁴ T₂ states. Finally, a pc-LED device was fabricated with the YAB:Cr³⁺ phosphor and blue chip, exhibiting the light out power of ~50.6 mW and energy conversion efficiency of ~17.4% at 100 mA drive current, respectively. The exceptional PL features including suitable excitation/emission wavelengths, suppressed thermal quenching and high QY make YAB:Cr³⁺ phosphors very promising for applications in plant growth pc-LEDs.     

红色荧光粉YAl3(BO3)4:Eu3+的制备及发光性能研究

以稀土氧化物、硝酸铝和硼酸为原料,高温固相反应制备了单相红色荧光粉YAl3(BO3)4:Eu3+,用X射线衍射和发射光谱对荧光粉末的结构和发光性能进行了分析.研究了煅烧温度、Eu3+掺杂量对其发光性能的影响.结果表明,反应物在1 250 ℃下煅烧可制得单相YAl3(BO3)4:Eu3+晶体,在YAl3(BO3)4:Eu3+晶体中,Eu3+取代了YAl3(BO3)4晶体中Y3+,占据了非对称中心格位.在394 nm的紫外光激发下,YAl3(BO3)4:Eu3+荧光粉具有很强的发光性能,与(Y,Gd)BO3:Eu3+荧光粉相比,最强发射线波长由596 nm变为618 nm,由橙红色光变为红色光,色纯度有了很大提高.Eu3+的最佳掺杂量为8%(物质的量分数).     

Synthesis and Photoluminescence Characteristics of YAl3(BO3)4:Tb3+ Phosphors by Combustion Process

Terbium‐activated YAl₃(BO₃)₄ (YAl₃(BO₃)₄:Tb³⁺) phosphors were synthesized by both combustion method and solid‐state reaction. It was found that the pure‐phase YAl₃(BO₃)₄ phosphors synthesized by combustion method were obtained at 1000°C, which was 200°C lower than that by solid‐state reaction. The average particle size of the combustion‐derived phosphors increased with increasing temperatures. The luminescence characteristics in ultraviolet (UV) — vacuum ultraviolet (VUV) ranges for the YAl₃(BO₃)₄:Tb³⁺ phosphors were investigated. The bands from 175 nm to 300 nm were attributed to the 4f⁸‐4f⁷5d¹ transitions of Tb³⁺. The other strong bands in the region from 125 nm to 175 nm were assigned to host absorption. The emission spectra showed the strongest emission at 542 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺. Moreover, the combustion‐derived YAl₃(BO₃)₄:Tb³⁺ phosphors generated more intense luminescence than the solid‐state‐derived phosphors under UV excitation.     

Enhanced afterglow behavior of a new Eu2+: NaBa4(BO3)3 yellow phosphor co-doped with different cations Dy3+, Ho3+and Nd3+

A new Eu²⁺: NaBa₄(BO₃)₃ phosphor, synthesized under conventional solid state approach, exhibits bright yellow persistent luminescence with the co-doping of Eu²⁺, Ln³⁺ (Ln = Dy³⁺, Ho³⁺, Nd³⁺). XRD investigation reveals that all samples are pure phase phosphors with cubic structure, indicating the doped Eu²⁺and Ln³⁺ cations were incorporated into the lattice that did not form inclusive phase in the material. Since there are two coordination forms ([EuO6] and [EuO8]) of Eu²⁺ cations in the matrix, the above yellow luminescence can be divided into two different emissions centering at 558 nm and 627 nm, confirming the crystallographic environment on the photoluminescence from Eu²⁺ center. Optimal doping concentrations for each cations were further determined as 2% atm for Eu²⁺, 2% atm for Dy³⁺, 3% atm for Ho³⁺ and 2% atm for Nd³⁺. Afterglow behaviors are also observed for samples with Ln³⁺ co-doping, which reveal typical double exponential decay model. Among the phosphors synthesized, the sample 2 at%Eu²⁺/3 at%Ho³⁺: NaBa₄(BO₃)₃ displays the best performance with higher initial brightness and longer lifetime, which can be attributed to the formation of electron traps with high concentration and suitable energy level, as confirmed by the result from thermal stimulated luminescence (TSL) analysis.     

Structural,thermal and thermoluminescence response of transition and alkaline earth metals activated on aluminium borate [Al2(B4O7)3:Mn,Mg]

Aluminium borate doped with manganese (Mn) and magnesium (Mg) at different concentrations are studied. The samples were synthesized by solid state sintering. The structure, morphology and crystallite size of the aluminium borate are affected by the dopants used. The crystallite size values calculated for different concentrations of manganese and magnesium used in doping of aluminium borate are within a range of 32.5–35.1 nm and 21.3–28.7 nm respectively. The particle size obtained using a scanning electron spectroscopy for Mn and Mg-doped aluminium borate are in the range of 30–40 nm and 20–30 nm respectively. A loss in weight from the thermal analysis performed for Mn and Mg-doped aluminium borate are observed to be 10.43% and 20.06%. The thermoluminescence glow peaks from all the samples measured at 1 °C.s^?1 following irradiation to 50 Gy showed a prominent glow peak at 96 °C with minor peak observed at higher temperature (178 °C) region of the glow curve. The activation energy for Mn and Mg-doped aluminium borate were determined to be approximately 0.78 ± 0.30 eV and 0.76 ± 0.25 eV by using the initial rise, glow curve deconvolution and variable heating rate method. The dose responses were considered from 1 to 300 Gy for Mn (0.4%) and Mg (0.3%) doped aluminium borate and were further studied by using the g(D) and f(D) functions.     

Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis

In present work, a series of Eu doped zinc borate, ZnB₂O₄, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB₂O₄ host lattice are studied for various beta doses ranging from 0.1 to 10?Gy. The high-temperature peak of Eu activated sample located at 192?°C exhibited a linear dose response in the range of 0.1–10?Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB₂O₄ were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu³⁺ ions located at 576–710?nm assigned to the ⁵D₀→⁷F_J (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ was reached Eu³⁺ concentration of 5?mol%; quenching occurred at higher concentrations. Strong emission peak for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ is observed. The CL experimental data indicate that ZnB₂O₄:Eu³⁺ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.     

Investigation of thermoluminescence and kinetic parameters of gamma ray exposed LiF: Sm3+, Eu3+ nanophosphors for dosimetric applications

Thermoluminescence (TL) properties of LiF: Sm³⁺ (0.05?mol%) co-doped with Eu³⁺ (0.02, 0.04, 0.06, 0.08?mol%) nanophosphor for the applications of TL dosimetry have been studied. The nanophosphors have been synthesized by chemical co-precipitation method at 8?pH value. The phase purity of the prepared samples has been confirmed by using X-ray diffraction (XRD) data. The XRD peaks broadening revealed the formation of the nanostructure, complemented by the TEM image. For TL studies, the samples have been irradiated with gamma rays using ⁶⁰Co source in the irradiation dose range of 0.1?kGy to 30?kGy. In gamma exposed samples, the TL glow curve consists of single glow peak at 410?K and three shoulder peaks at 475?K, 550?K and 632?K. The dosimetry properties such as the effects of exposure doses, heating rates and fading characteristics have also been studied. The kinetic parameters such as activation energy (E), the frequency factors (s) and order of kinetic (b) of the glow curves have also been calculated by using Chen's peak shape method. The linear behavior of TL intensity with radiation doses and low fading shows that the LiF: Sm³⁺, Eu³⁺ Nanophosphor is a potential candidate for dosimetry applications.     

Temperature-sensing characteristics of NaGd(MoO4)2: Sm3+, Tb3+ phosphors

In this study, Sm³⁺/Tb³⁺-co-doped NaGd(MoO₄)₂ phosphors were prepared via the hydrothermal method, with sodium citrate used as a chelator. X-ray diffraction confirmed the structure of the samples, and the test outcomes showed that the phosphors exhibited a body-centered tetragonal structure. Field-emission scanning electron microscopy results showed that the specimen morphology changed with the change in the Cit^3?/Re³⁺ molar ratio. Moreover, the measured temperature-dependent emission spectra showed that Sm³⁺ and Tb³⁺ had different quenching trends; thus, the fluorescence intensity ratio can be used to represent temperature. In addition, the outcome of this experiment revealed that the temperature-sensing sensitivity of the phosphors gradually increased with the increasing Cit^3?/Re³⁺ ratio, and the highest sensitivity value was 0.346 K^?1 (at 503 K, Cit^3?/Re³⁺ = 2). When the temperature was 298–369 K, the temperature-sensing relative sensitivity increased with increasing Cit^3?/Re³⁺, but in the range 374–503 K, the relative sensitivity decreased with increasing Cit^3?/Re³⁺. The highest relative sensitivity value of the sample was 2.7% K^?1 (404 K, Cit^3?/Re³⁺ = 0). Additionally, the Commission International del’Eclairage chromaticity coordinates displayed that the luminous colors of Sm³⁺/Tb³⁺-co-doped specimens continuously changed from green to red as the temperature changed.     

Thermoluminescence study of Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor via doping of singly,doubly and triply ionized ions

We report here thermoluminescence properties of Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor via doping of singly, doubly and triply ionized ions on the basis of PL studies done for this sample. The proposed sample was synthesized using solid state reaction method. Vibrational feature of this phosphor was confirmed by FT-IR spectra. This sample shows high degrees of crystallinity. All subseries are irradiated with ⁶⁰Co- γ (gamma) source and thermoluminescence studies were done for all subseries formed by doping of singly, doubly and triply ionized ions. The result shows that all the series give highest TL intensity at low dose rate. On doping of triply doped ionized ion (Y³⁺), TL intensity is enhanced to some extent. Deconvolution of broad TL glow data formed for some sample were done by using TLAnal computerized software. Thermoluminescence studies of these Eu³⁺ doped SrYAl₃O₇ phosphor were done by Nucleonix TL 1009I thermoluminescence (TL) reader. Trapping parameters of each phosphor such as activation energy (E), order of kinetics (b) and frequency factor (s) were calculated by Chen's peak shape method, Initial rise method and Ilich method. Thus, the singly, doubly and triply ionized ions co-doped with Na₂Sr₂Al₂PO₄Cl₉: Eu³⁺phosphor may be used in high dose thermoluminescence dosimetric application in various fields.     

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.     

Comprehensive study on structural,thermal, morphological and luminescence (RL,PL, TL) properties of CaLa2(WO4)4: Tb3+, Dy3+ phosphors synthesized via sol-gel method

Tb³⁺/Dy³⁺ co-doped CaLa₂(WO₄)₄ (CLW: Tb³⁺/Dy³⁺) and its derivatives were synthesized by the sol-gel method. The morphology, thermal, structure and luminescent-optical properties the as-prepared light-emitting phosphors were characterized by utilizing scanning electron microscopy (SEM), differential thermal analysis (DTA)-thermogravimetric analysis (TG), X-ray diffraction (XRD) and radioluminescence (RL or X-ray luminescence) - photoluminescence (PL) –thermoluminescence (TL or TSL) - optical absorption spectrometry. The Tb³⁺ and Dy³⁺ ions were singly or doubly doped and the results were examined in detail. Moreover, for these phosphors, the energy transfer mechanisms which depend on RL and PL spectra were determined. The samples excited by X-ray demonstrate characteristic luminescence peaks of Dy³⁺ (422, 480, 575, 663 and 747 nm) and Tb³⁺ (489, 544, 586, 620, 652 and 675 nm). These emissions are similar for RL and PL measurements. It could be said that the energy transfer efficiency of the host material is perfect for rare-earth ions. The synthesized phosphors exhibit various colors from yellow to blue under UV excitation. The optical band gaps of host CLW, CLW: Tb³⁺, CLW: Dy³⁺ and co-doped CLW: Tb³⁺/Dy³⁺ were calculated at values 3.83 eV, 3.44 eV, 3.64 eV and 3.52 eV, respectively. From the results obtained, the CaLa₂(WO₄)₄: Tb³⁺, Dy³⁺phosphors may be one of the potential candidates for light-emitting diode.     

Luminescent properties and energy transfer mechanism of NaGd(MoO4)2:Sm3+, Eu3+ phosphors

Sm³⁺ singly doped NaGd(MoO₄)₂ and Sm³⁺, Eu³⁺ co-doped NaGd(MoO₄)₂ phosphors by using sodium citrate as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). During the synthesis process, the Na₃Cit concentration plays a crucial role in determining the morphology and particle size of the products. The optimal doping concentration in Sm³⁺ singly doped NaGd(MoO₄)₂ phosphor was confirmed. The relevant parameters of energy transfer in the NaGd(MoO₄)₂: Sm³⁺, Eu³⁺ phosphors have been calculated based on the fluorescent dynamic analysis. Finally, on the analysis of luminescent spectra and fluorescent dynamics, the main energy transfer mechanism between Sm³⁺ and Eu³⁺ in NaGd(MoO₄)₂ phosphor is confirmed to be electric dipole-dipole interaction, and energy transfer pathway is from ⁴G_5/2 state of Sm³⁺ to ⁵D₀ state of Eu³⁺ rather than ⁵D₁ of Eu³⁺ ions.     

Synthesis,crystal structure,photoluminescence of Ba3Y2(BO3)4:Er3+ and thermal expansion of Ba3Y2(BO3)4

The Ba₃Y_2–xEr_x(BO₃)₄ (х = 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were obtained by crystallization from a melt. The Ba₃Y₂(BO₃)₄ crystal structure was refined from single crystal X-ray diffraction data to R = 0.037. Its anisotropic atomic displacement parameters for all atoms were refined for the first time. The borate crystallizes in the orthorhombic crystal system, space group Pnma with unit cell parameters a = 7.673(1), b = 16.44(1), c = 8.977(2) Å, V = 1132.3(3) ų, Z = 4. These phosphors are isotypical to those of the A₃M₂(BO₃)₄ (A = Ca, Sr, Ba, M = Ln, Y, Bi) family. The crystal structure contains the isolated BO₃ triangles, two general and a special one independent crystallographic sites for large cations, which are disordered over sites. Thermal behavior of Ba₃Y₂(BO₃)₄ was investigated by high-temperature X-ray powder diffraction and thermal expansion coefficients are calculated in a wide temperature range. An inflections of temperature dependencies of the unit cell parameters is observed in a range 600–740 °C. Luminescence spectra, excitation and kinetic curves of the Ba₃Y₂(BO₃)₄:Er³⁺ series are reported. A maximum luminescence intensity is observed for the x = 0.1 sample. According to vibrational spectroscopy data no structural changes upon activation of the Ba₃Y₂(BO₃)₄ matrix with the Er ions are observed.     

Synthesis and photoluminescence properties of Sr3(PO4)2:Re3+, Li+ (Re = Eu,Sm) red phosphors for white light-emitting diodes

Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) red phosphors were prepared via a high temperature solid state reaction, and their structure and luminescence properties were investigated. X-ray diffraction patterns indicate that the phase of as-prepared samples is in good agreement with standard Sr₃(PO₄)₂ structure. Under 395 nm excitation, the emission of Sr₃(PO₄)₂:Eu³⁺ consists of a strong peak centered at 622 nm and two weak peaks centered at 598 nm and 660 nm, which correspond to ⁵D₀→⁷F₂, ⁵D₀→⁷F₁ and ⁵D₀→⁷F₃ transitions, respectively. Also, the emission spectrum of Sr₃(PO₄)₂:Sm³⁺ shows three main peaks at 568 nm, 603 nm and 651 nm, which are attributed to ⁴G_5/2→⁶H_I/2 (I = 5, 7, 9) transitions of Sm³⁺. Furthermore, luminescence properties of Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) samples are enhanced significantly by Li⁺ ions doping as charge compensator. Results indicate that as-prepared Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) could be the potential red phosphors used in white light-emitting diodes.     

Luminescence investigations of novel orange‐red fluorapatite KLaSr3(PO4)3F: Sm3+ phosphors with high thermal stability

Single‐phase KLaSr₃(PO₄)₃F: Sm³⁺ phosphors with fluorapatite structure were prepared via high‐temperature solid‐state method in air atmosphere for the first time. The X‐ray diffraction, scanning electron microscope, diffuse reflectance spectra, photoluminescence spectra, and temperature‐dependent emission spectra, as well as lifetimes were measured to characterize the as‐prepared phosphors. Phase results indicated that KLaSr₃(PO₄)₃F: Sm³⁺ belongs to hexagonal system with a space group of P‐6. Photoluminescence measurements showed the emission spectrum was composed of four sharp peaks at about 564, 602 (the strongest one), 646, and 702 nm, corresponding to the ⁴G_5/2‐⁶H_J (J=5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺ ions. The optimum doping concentration of Sm³⁺ ions was turned out to be 0.03 (mol), and the mechanism of energy transfer among Sm³⁺ ions was considered to be dipole‐dipole interaction by using Dexter's theory. In addition, the critical distance R_c for energy transfer among Sm³⁺ ions were calculated to be 9.97 Å according to Blasse concentration quenching method. The selected KLa_0.97Sr(PO₄)₃F: 0.03Sm³⁺ exhibited high thermal stability with an activation energy of 0.163 eV. Besides, the Commission International de l'Eclairage chromaticity coordinate of the phosphor were located in the orange‐reddish light region.     

Synthesis and photoluminescence properties of CaGd2(MoO4)4:Eu3+ red phosphors

The novel red-emitting Eu³⁺ ions activated CaGd₂(MoO₄)₄ phosphors were prepared by a citrate sol–gel method. The X-ray diffraction patterns confirmed their tetragonal structure when the samples were annealed above 600 °C. The photoluminescence excitation spectra of CaGd₂(MoO₄)₄:Eu³⁺ phosphors exhibited the charge transfer band (CTB) and intense f–f transitions of Eu³⁺ ion. The optimized annealing temperature and Eu³⁺ ion concentration were analyzed for CaGd₂(MoO₄)₄:Eu³⁺ phosphors based on the dominant red (⁵D₀→⁷F₂) emission intensity under NUV (394 nm) excitation. All decay curves were well fitted by the single exponential function. These luminescent powders are expected to find potential applications such as WLEDs and optical display systems.     

Synthesis,energy transfer mechanism,and tunable emissions of novel Na3La(VO4)2:Re3+ (Re3+ = Dy3+, Eu3+, and Sm3+) vanadate phosphors for near-UV-excited white LEDs

In this study, novel Eu³⁺-, Dy³⁺-, and Sm³⁺-activated Na₃La(VO₄)₂ phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na₃La(VO₄)₂ phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O₈ and La(2)O₈ polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na₃La(VO₄)₂ compound was an excellent host for activating the luminescence of Eu³⁺ (614 nm), Dy³⁺ (575 nm), and Sm³⁺ (647 nm) ions. Further, Dy³⁺/Eu³⁺ co-doped Na₃La(VO₄)₂ phosphors were exploited, and the energy transfer from Dy³⁺ to Eu³⁺ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy³⁺ to Eu³⁺ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy³⁺/Eu³⁺ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.     

Luminescence properties and energy transfer of GdAl3(BO3)4:Ce3+, Tb3+ phosphor

Ce³⁺ and Tb³⁺ singly doped and co-doped GdAl₃(BO₃)₄ phosphors were synthesized by solid state reaction. The crystal structure, the luminescent properties, the lifetimes and the temperature-dependent luminescence characteristic of the phosphors were investigated. Through an effective energy transfer, the emission spectra of GdAl₃(BO₃)₄:Ce³⁺, Tb³⁺ phosphor contains both a broad band in the range of 330–400 nm originated from Ce³⁺ ions and a series of sharp peaks at 484, 541, 583, and 623 nm due to Tb³⁺ ions. The energy transfer from Ce³⁺ to Tb³⁺ in GdAl₃(BO₃)₄ host is demonstrated to be phonon assisted nonradiative energy transfer via a dipole–dipole interaction.     

Thermal stability and luminescence of novel garnet-type yafsoanite Ca3Zn3(TeO6)2:Sm3+ phosphors for white LEDs

In this study, novel garnet-type yafsoanite tellurate Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphors are successfully synthesized using the traditional high-temperature solid-state reaction. The phase purity of the obtained phosphors is analyzed by X-ray diffraction and Rietveld refinement studies. Morphological variations are also observed with the different concentrations of Sm³⁺ ions substitution, which is analyzed using Scanning Electron Microscopy (SEM). The photoluminescent properties of the phosphors are systematically investigated. Results show that the samples display the strongest emission peak at 612 nm under the near-ultraviolet (n-UV) 409 nm excitation. This peak can be ascribed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphor shows a high color purity, exhibits excellent thermal stability and good color drifting resistance. Furthermore, red and white light-emitting diodes have been successfully prepared. The white light-emitting diodes (w-LEDs) demonstrates a high color rendering index (CRI, R_a) and low correlated color temperature (CCT). This study introduces a new orange-red-emitting phosphor and discusses its application in herb-growth w-LEDs.     

Plant habitat-conscious phosphors: Tuneable luminescence properties of Dy3+-doped Ca8ZnY(PO4)7 phosphors by co-dopants Mg2+ and B3+

Outdoor lighting and other lighting systems can disrupt natural plant growth habits. Thus, LED lighting that is not detrimental to plant growth is required. In our study, Dy³⁺-doped Ca₈ZnY(PO₄)₇:Dy³⁺ phosphor with enhanced luminescence properties caused by the co-dopants Mg²⁺ and B³⁺ were synthesised. The samples had multiple excitation peaks, indicating they are excited by either near-ultraviolet (n-UV) or blue chips. All samples exhibited bright narrow yellow and blue emission corresponding to the transitions of Dy³⁺ ions with ⁴F_9/2→⁶H_13/2 and ⁴F_9/2→⁶H_13/2, respectively. Moreover, doping with Mg²⁺ and B³⁺ enhanced the luminescence intensity, reaching 113.6 and 119.7%, respectively. In addition, the luminescence emission intensity at 150 °C was maintained at approximately 95% of the initial value at 25 °C, and its thermal stability increased by 123%. Devices assembled with an n-UV chip (388 nm) and the as-obtained CZMYP:Dy³⁺ phosphor emitted a bright warm white light and simulated outdoor dark lighting for tobacco cultivation, indicating that the as-prepared phosphor is an excellent candidate material for plant habitat-conscious phosphors.