Synthesis of Ca3Sc2Si3O12:Ce3+ phosphor by hydrothermal Si alkoxide gelation

Single-phase Ca₃Sc₂Si₃O₁₂:Ce³⁺ green emission phosphor was synthesized by the hydrothermal silicon alkoxide gelation method. Such specimens demonstrated higher emission intensity than the Ca₃Sc₂Si₃O₁₂:Ce³⁺ samples that are prepared by conventional solid-state reaction method. It was also demonstrated that annealing in the presence of graphite as an oxygen scavenger significantly improves the fluorescence properties of this material.     

Structural and luminescence study of Ce3+ and Tb3+ doped Ca3Sc2Si3O12 garnets obtained by freeze-drying synthesis method

Ca₃Sc₂Si₃O₁₂ garnets doped with Ce³⁺ and Tb³⁺ ions were synthesized by a freeze-drying precursor method. The structural characterization was performed by X-ray diffraction (XRD) and Raman spectroscopy. Scanning Electron Microscopy (SEM) images of the calcined material were studied. High temperature treatments and doping with RE³⁺ ions resulted in a reduction of the secondary phases (Sc₂O₃) and an increase of the mean size of the nanocrystals, from 75 to 149 nm. These effects were confirmed by means of Raman spectra. Moreover, luminescence features of Ce³⁺ and Tb³⁺ doped samples indicated that these ions are effectively incorporated into the crystalline phase. In addition, the energy transfer processes between Ce³⁺ and Tb³⁺ ions in codoped garnets have been studied.     

Synthesis and photoluminescence properties of a cyan-emitting phosphor Ca3(PO4)2:Eu2+ for white light-emitting diodes

In this paper, a cyan-emitting phosphor Ca₃(PO₄)₂:Eu²⁺ (TCP:Eu²⁺) was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 250–450 nm region, but the emission spectrum is prominent at around 480 nm. The emission intensity of the TCP:Eu²⁺ was found to be 60% and 82% of that of the commercial BaMgAl₁₀O₁₇:Eu²⁺ (BAM) under excitation at 340 nm and 370 nm, respectively. Upon excitation at 370 nm, the absolute internal and external quantum efficiencies of the Ca₃(PO₄)₂:1.5%Eu²⁺ are 60% and 42%, respectively. Moreover, a white LED lamp was fabricated by coating TCP:Eu²⁺ with a blue-emitting BAM and a red-emitting CaAlSiN₃:Eu²⁺ on a near-ultraviolet (375 nm) LED chip, driven by a 350 mA forward bias current, and it produces an intense white light with a color rendering index of 75.     

Effects of fluxes on the synthesis of Ca3Sc2Si3O12:Ce3+ green phosphors for white light-emitting diodes

Different fluxes were added in preparation of Ca₃Sc₂Si₃O₁₂:0.01Ce³⁺ phosphors with a solid-state method and the different influences of the fluxes on phase formation, morphology, and photoluminescence properties of the phosphors were studied. The results show that CaF₂ flux is the best flux as it can decrease single phase-forming temperature, improve morphology and enhance photoluminescence of the Ca₃Sc₂Si₃O₁₂:0.01Ce³⁺ phosphors remarkably. White light-emitting diode was fabricated with the Ca₃Sc₂Si₃O₁₂:0.01Ce³⁺ phosphor prepared with CaF₂ flux, and good performances of this WLED confirm that CaF₂ is a good flux for preparing Ca₃Sc₂Si₃O₁₂:Ce³⁺, and the phosphor is an efficient green component for fabrication of white LEDs.     

Color-tunable emission and energy transfer studies in GdOBr:Ce3+ Dy3+ phosphor

Color-tunable blue to bluish white-emitting Ce³⁺/Dy³⁺ co-doped GdOBr phosphors have been synthesized by the conventional solid-state method. The phase structures, luminescent properties and energy transfer process were discussed in detail. Broad-band absorption originating from the f-d transition of Ce³⁺ can be found for the as-prepared GdOBr:Ce³⁺,Dy³⁺ phosphor, and color-tunable blue to bluish white emission can be realized owing to the energy transfer between Ce³⁺ and Dy³⁺. The energy transfer mechanism is demonstrated to be the dipole–dipole process. The energy transfer efficiency increases with increasing Dy³⁺ concentrations. The results indicate that Ce³⁺/Dy³⁺-activated GdOBr phosphors may be potential for phosphor-converted white-light UV-LEDs.     

Luminescence properties and energy transfer studies of a color tunable BaY2Si3O10:Tm3+,Dy3+ phosphor

A series of color-tunable and white light emitting phosphors BaY₂Si₃O₁₀:Tm³⁺,Dy³⁺ were synthesized by a high temperature solid-state reaction, and their phase structure, photoluminescence properties, and energy transfer processes between rare-earth ions were investigated in detail. Upon UV excitation, white light emission depending on dopant concentrations could be achieved by integrating a blue emission band located at 458 nm and an orange one located at 576 nm attributed to Tm³⁺ and Dy³⁺ ions, respectively. In addition, the energy transfer process between Tm³⁺ and Dy³⁺ ions was demonstrated to be a resonant type via a dipole–quadrupole mechanism. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for UV chip pumped white-light LEDs.     

Luminescence properties and energy transfer of Ba2Mg(PO4)2:Eu2+, Mn2+ phosphor synthesized by co-precipitation method

The Ba₂Mg(PO₄)₂:Eu²⁺, Mn²⁺ phosphor is synthesized by a co-precipitation method. Crystal phase, morphology, excitation and emission spectra of sample phosphors are analyzed by XRD, SEM and FL, respectively. The results indicate particles synthesized by a co-precipitation method have a smaller size in diameter than that synthesized by conventional solid-state reaction method. Emission spectra of BMP:Eu²⁺, Mn²⁺ phosphor show a broad blue and a broad yellow emission bands with two peaks at about 456 nm and 575 nm under 380 nm excitation. An overlap between Eu²⁺ emission band and Mn²⁺ excitation band proves the existence of energy transfer from Eu²⁺ to Mn²⁺. Emitting color of the BMP:Eu²⁺, Mn²⁺ phosphor could be tuned by adjusting relative contents of Eu²⁺ and Mn²⁺ owing to energy transfer formula. Therefore, BMP:Eu²⁺, Mn²⁺ may be considered as a potential candidate for phosphor for near-UV white LED.     

红色蓄光材料Y2O2S:Eu3+的硫熔法制备及其发光性能

用硫熔法制备了系列红色蓄光材料Y2O2S ：Eux^3＋（0．01≤x≤0．10）的多晶粉末样品并系统研究了其发光特性。XRD结果表明,晶胞参数c随着Eu^3＋含量的逐渐增大而增大,而晶胞参数α没有明显的线性变化关系,这与Y2O2S ：Eu^3＋的晶体结构有关。Y2O2S ：Eux^3＋（0．01≤x≤0．10）的激发光谱相似,在626nm发射光监控下最大激发波长约在330nm附近。在330nm激发下,随着Eu^3＋含量逐渐增大,发射光谱最强发射峰位置从540nm右移至626nm,观察到红色特征发射峰626nm的强度逐渐增大,在Eu^3＋含量为0．09时,其强度达到最大。在最佳合成条件及最佳Eu^3＋含量下,正在进行掺杂Mg^2＋和Ti^4＋及其发光特性的研究。     

BPO4@B2O3 and (BPO4@B2O3):Eu3+: The novel single-emitting-component phosphors for near UV-white LEDs

Nowadays much effort has been devoted to exploring novel luminescent materials with low-cost, high stability and excellent luminescent properties. In this paper, a new kind of luminescent material BPO₄@B₂O₃ was prepared by using a facile method. The as-obtained samples contain numerous BPO₄ nanoparticles enclosed by amorphous and crystalline B₂O₃ homogeneously, which exhibits a broad emission band ranging from 380 to 700 nm under near-UV irradiation. More importantly, it is worth noting that the BPO₄@B₂O₃ phosphor exhibits the excellent thermal quenching property, which endows it with a promising prospect as phosphors for high power white LEDs. To further promote its application as white light phosphors, Eu³⁺ ions were doped into the BPO₄@B₂O₃ samples and prepared the (BPO₄@B₂O₃):Eu³⁺ phosphors with chromaticity coordinates (0.3022, 0.3122). The corresponding packaging of LEDs indicates that both BPO₄@B₂O₃ and (BPO₄@B₂O₃):Eu³⁺ can be considered as the promising phosphors for WLEDs.     

Enhancement of blue-green photoluminescence in B2O3 fritted ZrO2:Ce3+ phosphor

Blue-green emission of ZrO₂:Ce³⁺ phosphor, prepared by solid-state reaction, is demonstrated. The phosphor presents a strong and broad photoluminescence band centered at 496 nm with excitation at 291 nm. The optimized Ce content is 2.5 mol% for the strongest emission of ZrO₂:Ce³⁺ phosphors prepared without B₂O₃. The PL intensity is enhanced by at least 3 dB by adding 5.0 mol% B₂O₃ within the ZrO₂:Ce³⁺ containing 5.0 mol% Ce during synthesis. Increase of the B₂O₃ flux effectively induces the Ce ions to substitute the Zr ions in ZrO₂ lattice and causes the ZrO₂ lattice distortion. The formation of Ce_0.75Zr_0.25O₂ compound within the ZrO₂:Ce³⁺ occurred when the Ce content is greater than or equal to 2.5 mol% for the phosphors prepared without B₂O₃ and leads to a degradation of the phosphor PL intensity due to the host effect. The addition of B₂O₃ during the preparation of phosphors containing Ce ions lower than or equal to 5.0 mol% essentially restrains the Ce_0.75Zr_0.25O₂ formation and then enhances the blue-green PL.     

Photoluminescence properties of Eu2+-activated Ca2Y2Si2O9 phosphor

Eu²⁺-activated Ca₂Y₂Si₂O₉ phosphors with different Eu²⁺ concentrations have been prepared by a solid-state reaction method at high temperature and their photoluminescence (PL) properties were investigated. Photoluminescence results show that Eu²⁺-doped Ca₂Y₂Si₂O₉ can be efficiently excited by UV–visible light from 300 to 425 nm. Ca₂Y₂Si₂O₉: Eu²⁺ exhibits broad band emission in the wavelength range of 425–700 nm, due to the 4f⁶5d¹ → 4f⁷5d⁰ transition of the Eu²⁺ ions located at two different sites ((Ca/Y)1 and (Ca/Y)2) in Ca₂Y₂Si₂O₉. The effect of the Eu²⁺ concentration in Ca₂Y₂Si₂O₉ on the PL properties was investigated in detail. The results showed that the relative PL intensity reaches a maximum at 1 mol% of Eu²⁺, and a red-shift of the emission bands from these two different sites was observed with increasing Eu²⁺ concentration. Also there exists energy transfer between these two Eu²⁺ sites. The potential applications of Ca₂Y₂Si₂O₉: Eu²⁺ have been pointed out.     

Luminescence properties and energy transfer investigations of Ce3+/Tb3+ co-doped BaY2Si3O10 phosphor

A novel phosphor BaY₂Si₃O₁₀ (BYSO): Ce³⁺, Tb³⁺ was synthesized by the conventional solid-state reaction, which displays tunable color emission from blue to blue-green under ultraviolet excitation by adjusting the radio of Ce³⁺ and Tb³⁺ appropriately. Photoluminescence characteristics were carefully investigated. We demonstrate the existence of efficient energy transfer from Ce³⁺ to Tb³⁺ in BaY₂Si₃O₁₀: Ce³⁺, Tb³⁺ phosphor. The energy transfer Ce³⁺ → Tb³⁺ was proved to be governed by dipole–quadrupole interaction.     

Synthesis and luminescence properties of CaAl2O4:Mn4+ phosphor

CaAl_2−yO₄:yMn⁴⁺ (y = 0–1.6 mol%) phosphors are synthesized by a solid-state reaction method in air, and their crystal structure and luminescence property are investigated. To compare luminescence property, CaAl_3.99O₇:1%Mn⁴⁺ and SrAl_1.99O₄:1%Mn⁴⁺ phosphors are also synthesized at the same condition. Broad band excitation spectra are observed within the range 220–550 nm, and emission spectra cover from 600 to 720 nm with the strongest emission peak at ∼658 nm owing to the ²E → ⁴A₂ transition of Mn⁴⁺ ion. The influence of crystal field to luminous intensity is discussed, and the possible luminous mechanism of Mn⁴⁺ ion is explained by using energy level diagram of Mn⁴⁺ ion. CaAl_1.99O₄:1%Mn⁴⁺, CaAl_3.99O₇:1%Mn⁴⁺, and SrAl_1.99O₄:1%Mn⁴⁺ phosphors under excitation 325 nm light emit red light, and their CIE chromaticity coordinates are (0.7181, 0.2813), (0.7182, 0.2818), and (0.7198, 0.2801), respectively. These contents in the paper are helpful to develop novel and high-efficient Mn⁴⁺-doped phosphor for white LEDs.     

Ratiometric optical thermometer with high-sensitive temperature sensing based on tunable luminescence of Ce3+-Eu2+ in KSr4B3O9 phosphors

It is a challenge to develop a new type of non-contact temperature sensor and the related materials with the advantages of high detection sensitivity, spatial resolution, non-invasive and fast response. In this work, a moderate solid-state method was utilized to prepare a novel Ce³⁺/Eu²⁺ co-doped KSr₄B₃O₉ phosphor for efficient dual-emission temperature-sensing application. According to the different activation energy and the energy transfer process from Ce³⁺ to Eu²⁺, two non-overlapping emission bands with respectively distinctive temperature responses were realized. By using the significant difference in the fluorescence intensity ratio between Eu²⁺ and Ce³⁺, a strong shift of the CIE coordinate from (0.3701, 0.4311) at 293 K to (0.2623, 0.2465) at 443 K could be read out. Meanwhile, the maximum absolute (S_a) and relative sensitivities (S_r) were fitted to be 0.0118 and 2.25 % K^?1 with a large chromaticity shift from 293 to 443 K (ΔE = 0.1652). The configuration coordinate diagram in KSr₄B₃O₉ was adopted to explain the temperature quenching mechanism in detail. The outstanding temperature-sensing characteristic indicates that KSr₄B₃O₉: 1.75 %Ce³⁺/1.75 %Eu²⁺ phosphor has the potential to be applied in a thermometric probe.     

微波法制备Gd2O2S:Tb3+荧光粉

首次用微波法成功制备了Gd2O2S:Tb3 荧光粉,分别用X射线衍射(XRD)、扫描电镜(SEM)、激光粒度仪对产物的晶相、形貌和粒度进行表征,用光致发射光谱(PL)和X射线激发的发射光谱(XEL)对产物的发光性能进行研究.结果表明,样品为单一六方结构的Gd2O2S,形貌完整,粒度分布均匀,D50=1.08μm,PL谱和XEL谱均呈现Tb3 的特征发射峰,最强峰为544nm的绿色发射峰.     

The role of Ga2O3 in the preparation of Y2O3:Eu3+ phosphor from the oxides

It has been observed that Ga₂O₃ enhances the cathodeluminescence and the 2537 Å-excited photoluminescence, and also causes whitening of the body colour of Y₂O₃:Eu²⁺ prepared from the oxides. In both types of luminescence, these effects are apparently due to the Ga₂O₃ behaving as a mineraliser, i.e. a diffusion enhancer. In the case of photoluminescence, additional brightness enhancement resulting from incorporation of Ga₂O₃ is due to a type of sensitisation to the exciting wavelength.     

A novel red phosphor Na2Ca4Mg2Si4O15:Eu3+ for plasma display panels

A novel red emitting phosphor, Eu³⁺-doped Na₂Ca₄Mg₂Si₄O₁₅, was prepared by the solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Na₂Ca₄Mg₂Si₄O₁₅:Eu³⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated a narrow size-distribution of about 300 nm for the particles with spherical shape. Upon excitation with vacuum ultraviolet (VUV) and near UV light, the phosphor showed strong red-emission lines at around 611 and 617 nm, respectively, corresponding to the forced electric dipole ⁵D₀ → ⁷F₂ transition of Eu³⁺, and the highest PL intensity at 617 nm was found at a content of about 8 mol% Eu³⁺. The optical properties study suggests that it is a potential candidate for plasma display panels (PDPs) application.     

Green light-emitting Lu3Al5O12:Ce phosphor powders prepared by spray pyrolysis

Green light-emitting Lu_2.985Al₅O₁₂:Ce_0.015 (LuAG:Ce) phosphor powders are prepared by spray pyrolysis. The only crystallized phase in the precursor powders and post-treated powders at temperatures below 800 °C is Lu₂O₃ and the other components are amorphous. Phase pure cubic garnet LuAG:Ce phosphor powders are obtained by post-treatment at 1000 °C. Phosphor powders post-treated at temperatures below 1400 °C retain the spherical shape of the precursor powders. The mean crystallite sizes of phosphor powders post-treated at 1200, 1400, and 1500 °C are 30, 46, and 54 nm, respectively. The excitation spectra contain two bands: a weak band with the maximum peak at 345 nm and a strong broad band in the spectral range from 400 to 490 nm with the maximum peak at 455 nm. The LuAG:Ce phosphor powders have broad emission spectra between 480 and 600 nm, with the maximum peak intensity located at 507 nm. The photoluminescence intensity of the phosphor powders post-treated at 1400 °C is 84.2% of that of the powders post-treated at 1500 °C.     

Effects of pressure on the emission of CaWO4:Eu3+ phosphor

CaWO₄:Eu³⁺ (Ca_0.925Eu_0.05WO₄) and CaWO₄ phosphors were synthesized by solid state method. Here, the pressure effect on the photoluminescence of CaWO₄:Eu³⁺ has been investigated with a diamond anvil cell up to 20 GPa at room temperature. It is observed that pressure has a great influence on the fluorescence intensity and the energy levels. With increasing pressure, the spectral features shift towards lower energies, and the ⁷F₁ multiplet will split into three Stark levels due to the removal of the degeneracy by the crystal-field interaction. In addition, the emission intensity of the ⁵D₀ → ⁷F₁ transition decreases significantly. Raman experiments further confirm the scheelite to wolframite structure transformation presents at around 10 GPa. Upon release of pressure, this high-pressure phase transforms back to the original scheelite phase, and continuously remains stable to ambient conditions.     

Luminescent properties of Ca2MgSi2O7 phosphor activated by Eu2+, Dy3+ and Nd3+

Long lasting alkaline earth silicates, Ca₂MgSi₂O₇:Eu,Dy,Nd was prepared under a reduction atmosphere through solid state reaction. The obtained phosphor was characterized by means of X-ray diffraction (XRD) and photoluminescence spectrum (PLS). The crystal structure of Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor was refined by Rietveld analysis. The obtained Ca₂MgSi₂O₇:Eu,Dy,Nd phosphor showed a yellow–green emission peaking at 518 nm, which is ascribed to the luminescent emission of the Eu²⁺ that occupied the octa-coordinated Ca²⁺ sites in the Ca₂MgSi₂O₇ host. The electron affinity (ea) value for Eu²⁺ in [EuO₈] was calculated to 1.9 eV. The decay profile and the emission spectrum indicated that when the value of Dy/Eu is increasing, there is a concentration quenching of Eu²⁺.