Design of Eu2+-activated broadband orange-emitting phosphors with excellent luminescent performance for warm WLEDs

We report orange-emitting Sr₈La_0.5Na_0.5Mg_1.5(PO₄)₇:Eu²⁺ (SLNMPO-0.5:Eu²⁺) and Sr₇LaNaMg_1.5(PO₄)₇:Eu²⁺ (SLNMPO-1:Eu²⁺) phosphors with broad emission bands covering from 450 to 800 nm. The phosphors can be excited by n-ultraviolet and blue light efficiently. Their crystal structure, diffuse reflection spectra, photoluminescence (PL) spectra, fluorescence decay curves and thermal stability were investigated systematically. Under the excitation of 365 and 400 nm, SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ both exhibit better PL properties and contain more red emissions than SMPO:Eu²⁺. CIE coordinates of SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ under 365 nm excitation are (0.460, 0.497) and (0.457, 0.494), respectively. Furthermore, high-quality warm white light can be generated by fabricating warm white light-emitting diode (WLED) devices with 370 nm LED chips, BaMgAl₁₀O₁₇:Eu²⁺ commercial blue phosphor and orange-emitting SLNMPO-0.5:Eu²⁺ (or SLNMPO-1:Eu²⁺) phosphor. The correlated color temperature, R_a and color coordinates are 3880 K, 94.05, (0.3895, 0.3922) and 3736 K, 91.73, (0.4005, 0.4078) for the fabricated WLED devices with SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺, respectively. The excellent performances indicate that SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ have great potential to be attractive candidates in the application of warm WLEDs.     

Luminescence and temperature-sensing properties of Y4GeO8:Bi3+,Eu3+ phosphor

In this paper, Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor with dual emission centers was elaborated via conventional solid-state reaction technology. Thorough research on the structure, morphology, and luminous properties of Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor, the potential applications in optical thermometry were investigated by means of fluorescence intensity ratio and thermochromic techniques. Under 290 and 347 nm excitation, Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor presents broadband emission from ³P₁ → ¹S₀ transition of Bi³⁺ ions and characteristic emission peaks from 4f–4f transition of Eu³⁺ ions. Outstanding temperature-sensing capabilities are acquired from Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor. The maximum relative sensitivity (S_r) can attain 1.51% K⁻¹ (λ_ex = 290 nm). With temperature raising (303–513 K), the emitted color of Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor (λ_ex = 290 nm) shifts from faint yellow to red with a high chromaticity shift (0.180), which can be distinguished by the unaided eye clearly. Our results indicate that Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor has potential applications in optical temperature measurement and high-temperature safety marker.     

Mn2+/Pr3+/Tb3+ single-doped Mg4Ga4Ge3O16 persistent luminescence materials for optical information storage application

Persistent luminescence (PersL) phosphors are considered as promising candidates for the next generation of information storage medium. Mg₄Ga₄Ge₃O₁₆ (MGG) is an electron trapping material which exhibits defect luminescence, and the luminescent properties are easily tuned via doping various activated ions. In this work, undoped and Mn²⁺/Pr³⁺/Tb³⁺ single-doped MGG phosphors were synthesized via high temperature solid phase reactions. X-ray diffraction and scanning electron microscope results confirm that the activated ions tend to occupy Mg²⁺ sites. Excited at 265 nm, the MGG host exhibits a defect emission band peaked at 450 nm. Red, pink and green emissions are observed in the Mn²⁺/Pr³⁺/Tb³⁺ single-doped MGG samples, which are ascribed to the Mn²⁺: ⁴T₁(G) → ⁶A₁(S), Pr³⁺: ¹D₂ → ³H₄ and Tb³⁺: ⁵D₄ → ⁷F₅ transitions, respectively. All the samples exhibit bright PersL for minutes after the cessation of excitation. The energy transfer, concentration quenching, luminescence decay and afterglow mechanisms are also discussed in detail. The phosphors exhibit efficient thermal and optical stimuli response, showing great potentials in the optical information storage.     

Upconversion thermal enhancement of 2H11/2→4I15/2 of Er3+ and blue emission of impurity Tm3+ in Sr3(PO4)2:Er3+/Yb3+

A series of Sr_2.99-x(PO₄)₂:.01Er³⁺/xYb³⁺ (x = .02, .04, .06, .08, .10) phosphors in the presence of impurity Tm³⁺ were synthesized by high temperature solid-state method, and X-ray diffraction results show that these samples are pure R-3 m(166) space group phase. The upconversion luminescence (UCL) of Er³⁺ and impurity Tm³⁺ under 980-nm laser excitation were investigated, and the results show that the intense blue UCL of impurity Tm³⁺ and thermal enhancement of ²H_11/2→⁴I_15/2 of Er³⁺ simultaneously exist. When Er³⁺ doping concentration is kept at .01, both the blue UCL intensity of impurity Tm³⁺ and green and red UCL intensity of Er³⁺ reach the maximum at Yb³⁺ doping concentration of .08. The thermal enhancement effect of ²H_11/2→⁴I_15/2 of Er³⁺ was observed as high as 3.27 times from 303 to 723 K, which is because of lattice distortion and phonon-assisted transition. In addition, the optical temperature performance of Sr_2.91(PO₄)₂:.01Er³⁺/.08Yb³⁺ sample was studied, and the maximum absolute temperature sensitivity was calculated as .00623 K⁻¹ at 538 K. This study suggests that Sr₃(PO₄)₂:Er³⁺/Yb³⁺ phosphors in the presence of impurity Tm³⁺ have a promising application prospect as optical temperature sensor at high temperature.     

Synthesis,crystal structure,and anti-thermal quenching performance of Lu2Sr(1−x)Al4SiO12:xEu2+ phosphors

With high-temperature solid-state reaction method, a series of Lu₂Sr_(1−x)Al₄SiO₁₂:xEu²⁺ phosphors have been synthesized. With Rietveld refinement method, the crystal structure of Lu₂SrAl₄SiO₁₂ has been refined. Under the excitation of the ultraviolet and violet band light, Lu₂Sr_(1−x)Al₄SiO₁₂:xEu²⁺ emits the Eu²⁺ characteristic blue broadband light. The photoluminescence properties of concentration quenching, emission peak shift, reflectance spectra, and luminescence decay have been investigated. With the structure analyses, the corresponding physical mechanisms have been discussed. With the increased temperature, this phosphor shows well thermal stabilities. For the x_Eu = 0.06, 0.08, and 0.1 phosphors, the strong anti-thermal quenching performance has been observed. The reason for the anti-thermal quenching of this phosphor has been discussed. The trap capture mechanism may be the suitable physical mechanism to explain the anti-thermal quenching of this phosphor. This phosphor shows the potential applications in the white LED lighting fields.     

Photoluminescence properties of Eu-doped WO3-Eu2(WO4)3 composites and single-phase Eu2(WO4)3 powders

The development of highly stable and efficient oxide-based red phosphors is urgently required for next-generation lighting devices. Herein, we report the micro/crystal structures and luminescent properties of single-phase Eu₂(WO₄)₃ and Eu³⁺-doped WO₃-Eu₂(WO₄)₃ composite phosphors prepared by a one-step conventional solid-state reaction method in air atmosphere. As increasing Eu contents in the mixtures of WO₃ and Eu₂O₃, the intensities of the X-ray diffraction peaks of Eu₂(WO₄)₃ increased while that of WO₃ decreased. The photoluminescence intensity of the synthesized phosphors increased with increase in the Eu content when calcined at 900 °C, while it degraded at a higher temperature. Red-emitting single-phase Eu₂(WO₄)₃ powders were successfully obtained when the WO₃ and Eu₂O₃ powders were calcined in the ratio of 3:1. The intensity of the red emission spectra of the Eu₂(WO₄)₃ phosphor was higher than those of the 6, 12, and 24 at.% Eu-added WO₃ composites at excitation wavelengths of 394 and 465 nm. On the other hand, the intensity of emission from the single-phase phosphor was lower than that of the Eu-doped WO₃-Eu₂(WO₄)₃ composites under excitation of UV light at 254 nm. Thus, we propose two prospective phosphors for application as red phosphors at various wavelengths.     

Local charge regulation by doping Li+ in BaGa2O4:Bi3+ to generate multimode luminescence for advanced optical Morse code

In the field of advanced anti-counterfeiting research, it is a hot issue to develop a multimodal anti-counterfeiting material with adjustable luminescence characteristics. Here, persistent luminescent materials of BaGa₂O₄:xBi³⁺ (x = 0-0.02) and BaGa₂O₄:0.005Bi³⁺,yLi⁺ (y = 0.001–0.02) were synthesized by a solid state reaction at high temperature. BaGa₂O₄: Bi³⁺ exhibited a broad blue emission at ～470 nm (transition from [GaO₄]) and a sharp NIR emission at ～710 nm (³P₁→¹S₀ transition of Bi³⁺), upon UV excitation at 250 nm. Incorporation of Li⁺ in BGO: 0.005Bi³⁺ induced the emission color shifting from blue to green. After stoppage of UV excitation, the BGO:0.005Bi³⁺ exhibited white afterglow with emission peaks at the range of 500–700 nm. However, incorporation of Li⁺ leaded to a stronger green afterglow and a weaker NIR afterglow. When the afterglow disappeared, the sample outputted afterglow again after heating processing. The prepared samples exhibited time- and temperature-dependent multimode luminescence, so they were used as components, combined with Morse code to realize multi-modal dynamic anti-counterfeiting. The outcomes in this work indicate that the prepared luminescent materials have broad prospects in advanced anti-counterfeit applications.     

电荷补偿剂对Sr2MgSi2O7：Eu3＋红色发光粉结构和性能的影响

采用微波辅助凝胶燃烧法制备Sr2MgSi2O7：Eu3＋,R＋（R=Li,Na,K）系列红色发光粉,通过X射线粉末衍射、荧光分光光度计等分析表征荧光粉的结构以及发光性能。结果表明：Sr2MgSi2O7：Eu3＋,R＋（R=Li,Na,K）系列红色发光粉的晶体结构与Sr2MgSi2O7的相同,属四方晶系;加入电荷补偿剂L...     

纤维素―铝酸锶复合膜的制备及表征

将微晶纤维素溶解于氯化1-正丁基-3-甲基咪唑([Bmim]Cl)离子液体中,加入铝酸锶荧光粉,然后流延成膜,制备得到了纤维素―铝酸锶复合膜。利用红外光谱、X射线衍射、热重分析、扫描电镜和荧光发射光谱对复合膜进行了表征。结果表明,铝酸锶荧光粉在纤维素膜中分布均匀,铝酸锶荧光粉和纤维素之间存在着一定的相互作用,纤维素对荧光粉体发光影响较小。     

碱土铝酸盐蓄光型发光材料的后处理研究

采用胶体包覆和表面成膜包覆相结合的方法,对碱土铝酸盐蓄光型发光材料进行包覆后处理研究。分析了包覆后处理对材料表面结构变化、发光性能及应用性能的影响。研究表明:经过包覆后处理的发光材料在水中浸泡时,发光材料对水能保持稳定,水相的pH值和电导率保持基本稳定;而未经包覆后处理的发光材料在水中分解,其水相的pH值和电导率上升很快。经过包覆处理的SrAl_2O_4:Eu,Re(Re为稀土元素)(PLO)在水中浸泡720 h后能保持80％的初始亮度,未经处理的发光材料则失去发光性能。包覆后处理能在发光材料表面形成了一层连续的比较致密的保护层,有效地减少外界对发光材料的影响,而且可以修复发光材料颗粒原有的裂纹等缺陷。包覆处理后能有效提高发光材料的应用性能,如耐水性、分散性及耐高温性能,更能适应不同的应用领域。