New Phosphors for White LEDs

White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or UV LEDs) and photoluminescence phosphors. GaN-based highly efficient blue InGaN LEDs combined with phosphors can produce white light. These solid-state LED lamps have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability, and long operating lifetime (about 100,000 hours). For the purpose of development of high energy-efficient white light sources, we need to produce highly efficient new phosphors, which can absorb excitation energy from blue or UV LEDs and generate emissions.In this paper, we investigate the development of blue or UV LEDs by the appropriate combination of new phosphors which can lead us to obtain high brightness white light. The criteria of choosing the best phosphors, for blue (380-450 nm) and UV (360-400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance light between the light emission from blue LEDs and the yellow YAG:Ce,Gd phosphor is important to obtain white light with high color temperature. The phosphors with high efficiency which can be excited by UV LEDs are important to obtain the white light with high color rendering index.     

一种新的橙红色长余辉荧光材料Y2O2S∶Sm3+

铜激活的硫化锌(ZnS∶Cu)和铕激活的硫化钙(CaS∶Eu)是最早获得应用的蓝色和红色长余辉材料. 随后, 相继发现了铝酸盐体系和硅酸盐体系两大类长余辉荧光材料[1～3]. 这两类长余辉荧光材料在发光亮度、余辉时间、稳定性方面都较前述硫化物系列长余辉荧光材料有很大提高, 从而具有非常广阔的应用前景和应用范围[4～6]. 但这两类长余辉荧光材料的发光颜色一般为蓝紫、蓝或黄绿, 没有红色发光现象. 随着研究的深入, 人们发现了稀土元素激活的碱土钛酸盐红色长余辉荧光材料, 这种荧光材料在发光亮度及余辉上都有明显的提高[7,8], 而且解决了硫化物不稳定的缺点. 近年来才发展起来的以碱土金属氧化物为发光基质, 以Eu3+为激活剂的红色长余辉荧光材料进一步提高了余辉亮度及时间[9].     

Improved water resistance of SrAl2O4: Eu2+, Dy3+ phosphor directly achieved in a water-containing medium

In this paper, a heterogeneous precipitation method utilizing urea hydrolysis was adopted to coat a SiO₂ layer on the surface of SrAl₂O₄:Eu²⁺, Dy³⁺ long persistence phosphors. To avoid phosphor hydrolysis in a water-containing coating medium, the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) were concerned and carried out. The crystal phases, surface morphologies, hydrolysis stability and water resistance on afterglow properties of coated phosphors were investigated. Scanning electron microscopy, energy dispersive spectrum analysis, transmission electron microscope and Fourier transform infrared spectrum results confirmed that a continuous, uniform and compact SiO₂ coating layer was successfully obtained on the phosphors surface. A theoretical coating amount of 5% or higher was found to be good for hydrolysis stability. Photoluminescence results revealed the coated phosphors showed much better water resistance on afterglow properties than the uncoated phosphor. We also discussed and proposed the hydrolysis restriction mechanism of SrAl₂O₄:Eu²⁺, Dy³⁺ in the water-containing coating medium.     

掺铥硫氧化钇的特殊余辉性质

迄今为止,稀土长余辉磷光体已见文献或专利公开报道的激活离子主要有适于紫外光激发的三价铈离子(Ce³⁺)和三价镨离子(Pr³⁺)、适于可见光激发的铕离子(Eu³⁺和Eu²⁺)及钐离子(Sm³⁺,Sm²⁺),尚未涉及到铥离子Tm³⁺或Tm²⁺.我们在Tm³⁺离子激活的硫氧化钇体系Y₂O₂S:Tm³⁺中发现了长余辉荧光特性.特别是在该磷光体中还发现了一种非常特殊的余辉现象.     

白光LED用黄色荧光粉Ba(Y1-0.5x-yAly)2S4:xHo3+的合成和发光特性

采用高温固相法合成了Ba(Y1-0.5x-yAly)2S4:xHo3+系列荧光粉。在465 nm蓝光激发下,荧光粉的发射光谱呈多谱带发射,主峰位于492、543和661 nm处,分别对应于Ho3+的5F3→5I8,(5S2,5F4)→5I8和5F5→5I8跃迁发射。研究了Ho3+和Al3+掺杂量对BaY2S4:Ho3+发光性能的影响。结果表明,随着Ho3+掺杂量的逐渐增大,荧光粉的发光颜色由绿色逐渐向红色转变;适量Al3+取代Y3+可以提高BaY2S4:Ho3+荧光粉的发光强度。荧光粉Ba(Y0.665Al0.3)2S4:0.07Ho3+在蓝光(465 nm)激发下发射黄光,是一种潜在的白光LED用黄色荧光粉。     

Tb3+，Sm3+掺杂的YNbO4多色荧光材料的制备及发光性能

采用溶胶-凝胶法合成了YNbO4∶Tb^3+,Sm^3+系列荧光粉。光谱测试表明:体系中的NbO43-基团能够吸收紫外光并将能量传递给Tb^3+和Sm^3+,从而增强荧光粉的发光强度。在290 nm激发下,YNbO4∶Tb^3+,Sm^3+荧光粉的发射光谱中既出现了Tb^3+的绿光发射又出现了Sm^3+的橙光发射。通过改变Sm^3+的掺杂浓度,实现了荧光粉发射光的光色可调。     

新型双钼酸盐红色荧光粉的制备及发光性能研究

采用高温固相法合成了一种新型的白光LED用双钼酸盐红色荧光粉,利用XRD,F-4500等对其进行了研究。结果表明:该系列荧光粉可以被近紫外光(396 nm)和蓝光(466 nm)有效激发,发射峰值位于615 nm(Eu3+离子的5D0→7F2跃迁)的红光;而且在钾铕双钼酸盐荧光粉KEu(MoO4)2中引入适量的钨酸能加强其发光强度,而不改变样品的发射光谱的形状和发射峰的位置。此外,在确定WO24-/MoO42最佳比值的前提下,文章还详细探讨了碱金属离子相互置换对样品发光性能影响的机制。     

Origin of Thermal Degradation of Sr(2-x)Si(5)N(8):Eu(x) Phosphors in Air for Light-Emitting Diodes

The orange-red emitting phosphors based on M(2)Si(5)N(8):Eu (M = Sr, Ba) are widely utilized in white light-emitting diodes (WLEDs) because of their improvement of the color rendering index (CRI), which is brilliant for warm white light emission. Nitride-based phosphors are adopted in high-performance applications because of their excellent thermal and chemical stabilities. A series of nitridosilicate phosphor compounds, M(2-x)Si(5)N(8):Eu(x) (M = Sr, Ba), were prepared by solid-state reaction. The thermal degradation in air was only observed in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10, but it did not appear in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.02 and Ba analogue with x = 0.10. This is an unprecedented investigation to study this phenomenon in the stable nitrides. The crystal structural variation upon heating treatment of these compounds was carried out using the in situ XRD measurements. The valence of Eu ions in these compounds was determined by electron spectroscopy for chemical analysis (ESCA) and X-ray absorption near-edge structure (XANES) spectroscopy. The morphology of these materials was examined by transmission electron microscopy (TEM). Combining all results, it is concluded that the origin of the thermal degradation in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10 is due to the formation of an amorphous layer on the surface of the nitride phosphor grain during oxidative heating treatment, which results in the oxidation of Eu ions from divalent to trivalent. This study provides a new perspective for the impact of the degradation problem as a consequence of heating processes in luminescent materials.     

Morphology control and luminescence properties of BaMgAl10O17:Eu phosphors prepared by spray pyrolysis

Starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives, BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺) phosphors were prepared by a two-step spray pyrolysis (SP) method. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra were used to characterize the resulted BAM:Eu²⁺ phosphors. The obtained BAM:Eu²⁺ phosphor particles have spherical shape, submicron size (0.5-3 μm). The effects of process conditions of the spray pyrolysis, such as molecular weight and concentration of PEG, on the morphology and luminescence properties of phosphor particles were investigated. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.03 g/ml in the precursor solution. Moreover, the emission intensity of the phosphors increased with increasing of metal ion concentration in the solution. Compared with the BAM:Eu²⁺ phosphor prepared by citrate-gel method, spherical BAM:Eu²⁺ phosphor particles showed a higher emission intensity.     

Full‐Spectrum Persistent Luminescence Tuning Using All‐Inorganic Perovskite Quantum Dots

Applications of persistent luminescence phosphors as night or dark‐light vision materials in many technological fields have fueled up a growing demand for rational control over the emission profiles of the phosphors. This, however, remains a daunting challenge. Now a unique strategy is reported to fine‐tune the persistent luminescence by using all‐inorganic CsPbX₃ (X=Cl, Br, and I) perovskite quantum dots (PeQDs) as efficient light‐conversion materials. Full‐spectrum persistent luminescence with wavelengths covering the entire visible spectral region is achieved through tailoring of the PeQD band gap, in parallel with narrow bandwidth of PeQDs and highly synchronized afterglow decay owing to the single energy storage source. These findings break through the limitations of traditional afterglow phosphors, thereby opening up opportunities for persistent luminescence materials for applications such as a white‐emitting persistent light source and dark‐light multicolor displays.     

Photoluminescent properties of white-light-emitting Li6Y(BO3)3:Dy3+ phosphor

In this study, lithium yttrium borate (LYBO) phosphor was doped with various concentrations of trivalent dysprosium ions. To produce these phosphors, the raw materials were sintered. The phase conformation, crystallinity, grain size, and overall morphology of the synthesized phosphors were studied with X-ray diffraction and scanning electron microscopy. The optimized LYBO phosphor, i.e., the LYBO phosphor that exhibited the highest X-ray- and ultraviolet (UV)-induced photoluminescent intensities, had a Dy³⁺ concentration of 4 mol%. Photoluminescence analysis showed that this phosphor could be easily excited with near-UV light (300–400 nm). The dominant photoluminescence bands were found in the blue (480 nm) and yellow (577 nm) regions of the visible spectrum. The light yield of the X-ray-induced luminescence of the optimized Li₆Y(BO₃)₃:Dy³⁺ was found to be 66% of that of the commercially available X-ray imaging material, Gd₂O₂S:Tb³⁺ (GOS). The chromaticity coordinates of the Li₆Y(BO₃)₃:Dy³⁺ phosphor were x = 0.34 and y = 0.32, which agree well with achromatic white (x = 0.33, y = 0.33). The results of this study show that the synthesized Li₆Y(BO₃)₃:Dy³⁺ phosphor could be used as X-ray imaging material.     

New SrAl2B2O7:Eu2+, Mn2+ phosphors for white light-emitting diodes

A series of Eu(2+) and Mn(2+) co-doped SrAl(2)B(2)O(7) phosphors were prepared by solid-state reaction method. X-ray powder diffraction (XRD) and photoluminescence excitation and emission were employed to characterize the phosphors. The results show that energy transfers between Eu(2+)and Mn(2+) ions. As the content of Ca(2+) ions in Ca(x)Sr(0.92-x)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphors increased, the CIE coordinates decreased and close to the white color standard mandated by the National Television Standard Committee (NTSC). Meanwhile, a white LED (light-emitting diode) was fabricated by combining the Ca(0.5)Sr(0.42)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphors with a 370 nm InGaN chip. The color coordinate of the fabricated white LED was also close to the white color standard, indicating that the Ca(0.5)Sr(0.42)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphor is a promising single-host phosphor that can be used in white LEDs.     

Waterproof Alkyl Phosphate Coated Fluoride Phosphors for Optoelectronic Materials

A facile approach for coating red fluoride phosphors with a moisture‐resistant alkyl phosphate layer with a thickness of 50–100 nm is reported. K₂SiF₆:Mn⁴⁺ particles were prepared by co‐precipitation and then coated by esterification of P₂O₅ with alcohols (methanol, ethanol, and isopropanol). This route was adopted to encapsulate the prepared phosphors using transition‐metal ions as cross‐linkers between the alkyl phosphate moieties. The coated phosphor particles exhibited a high water tolerance and retained approximately 87 % of their initial external quantum efficiency after aging under high‐humidity (85 %) and high‐temperature (85 °C) conditions for one month. Warm white‐light‐emitting diodes that consisted of blue InGaN chips, the prepared K₂SiF₆:Mn⁴⁺ phosphors, and either yellow Y₃Al₅O₁₂:Ce³⁺ phosphors or green β‐SiAlON: Eu²⁺ phosphors showed excellent color rendition.     

一种上转换白光荧光粉的制备与发光性能研究

采用高温固相法制备了上转换白光荧光粉AlF3-YbF3:Er3+/Tm3+。通过XRD物相分析可知:上转换白光荧光粉AlF3-YbF3:Er3+/Tm3+是由三方AlF3相和正交YbF3相组成;利用发射光谱研究了该荧光粉的上转换发光性能,并且分析了当固定Er3+离子掺杂浓度时,Tm3+离子掺杂浓度对上转换白光荧光粉AlF3-YbF3:Er3+/Tm3+色度的影响,进而提出其上转换能量传递机制。结果表明:在980 nm激光激发下,波长为410 nm的紫光峰、550 nm的绿光峰和660 nm的红光峰分别对应于荧光粉中Er3+离子的2H9/2→4I15/2,4S3/2→4I15/2和4F9/2→4I15/2能级的跃迁,而波长为360 nm的紫外光峰、450 nm的蓝光峰、700 nm的红光峰,分别对应于荧光粉中Tm3+离子的1D2→3H6,1G4→3H6和1G4→3F4能级的跃迁,Er3+离子发出的光与Tm3+离子发出的光最终混合成色坐标为x=0.32,y=0.36的白光。此外,通过980 nm半导体激光器和EPM 2000 Dual-channel Joulemeter/Power meter测得该荧光粉最大上转换效率为6.90%。     

Preparation of blue-emitting CaMgSi2O6:Eu phosphors in reverse micellar system and their application to transparent emissive display devices

Blue-emitting Eu²⁺-doped CaMgSi₂O₆ phosphors were prepared by the reverse micelle method. The resultant particles were nanocrystalline with a grain size of about <300 nm and exhibited a characteristic blue emission spectrum centered at 445 nm induced by the oxygen coordinated Eu²⁺ ions. By using the corresponding nanophosphors followed by the formation of a uniform phosphor layer, we have demonstrated the mini-sized transparent plasma-discharge panels and investigated their luminance characteristics. Phosphor coated panel is properly transparent, ≥65%, at the visible wavelength region and illuminates a characteristic blue emission under Ne/Xe plasma discharge conditions. Thus, we can obtain a fast decaying, robust blue-emitting silicate phosphor layer under excited plasma radiation for upcoming emissive display devices like as transparent and three-dimensional plasma display panels.     

Synthesis,luminance and ultraviolet resistance of a copolymer phosphor of Eu-complex and siloxane in near UV-based LED

Research on Chemical Intermediates - In copolymer phosphors with Eu(III), the majority have difficulty in resisting aging by UV light. In this paper, a novel copolymer phosphor with high thermal...     

Surface-treatment of Alkaline Earth Sulfides Based Phosphor

A series of alkaline earth sulfides based phosphors Ca0.8Sr0.2S : Eu^2 , Tm^3 were covered with a layerof protective coating with alkaline earth fluorides by heating the mixture of phosphor and NH4HF2 at elevatedtemperatures. The coatings were characterized by means of XRD and SEM. The optical properties of thecoated phosphors and the influences of the coating on their properties have been discussed extensively. Thestabilities of the coated and uncoated phosphors have been compared.     

Ca[B8O11(OH)4] : Eu2+ – A Highly Efficient Deep Blue-Emitting Phosphor Prepared by Low-Temperature Self-reduction

Highly efficient inorganic phosphors are crucial for solid-state lighting. In this paper, a new method of low-temperature self-reduction was used for preparing a highly efficient deep blue-emitting phosphor of Ca[B₈O₁₁(OH)₄] : Eu²⁺ (CBH : Eu²⁺). The crystal structure, morphology, chemical state, and photoluminescence (PL) properties of the CBH : Eu²⁺ phosphor have been investigated. By using the screened hybrid function (HSE06), the band gap (E_g) of CBH was calculated to be 7.48 eV, which is a necessary condition for achieving high quantum yield phosphors. The experiment results show that almost all the added raw materials of Eu³⁺ can be reduced to Eu²⁺ in CBH crystal under a non-reducing atmosphere. The CBH : Eu²⁺ phosphor shows a broad excitation spectrum centered at 277 and 327 nm in the range of 220 to 400 nm, and a narrow-band emission spectrum centered at 428 nm in the range of 400 to 500 nm, with a full width at half maximum (fwhm) of 42.35 nm. Under UV radiation, the CBH : 2 %Eu²⁺ exhibits high photoluminescence quantum yield (PLQY=95.0 %), high external quantum efficiency (EQE=31.1 %), and ultra-high color purity (97.6 %). The PL intensity of CBH : 2 %Eu²⁺ remains 62.6 % of the initial intensity at 150 °C. Finally, the white light-emitting diodes (WLED) fabricated by CBH : 2 %Eu²⁺, excited by a 365 nm chip, presents outstanding performances with a luminous efficacy (LE) of 13.9 lm/W, a color rendering index (CRI) of 89.4, and a correlated color temperature (CCT) of 5825 K. The above results show that CBH : Eu²⁺ can be used as a promising blue phosphor for WLED. This new method of low-temperature self-reduction can be applied to design and prepare other new types of highly efficient phosphors.     

A Novel White Light Emitting Long-lasting Phosphor

A novel white light emitting long-lasting phosphor Cd1-xDyxSiO3 is reported in this letterThe Dy^3 doped CdSiO3 phosphor emits white light. The phosphorescence can be seen with the naked eye in the dark clearly even after the 254nm UV irradiation have been removed for about 30min. In the emission spectrum of 5% Dy^3 doped CdSiO3 phosphor, there are two emission peaks of Dy^3 , 580nm (^4F9/2→^6H13/2) and 486nm (^4F9/2→^6H15/2), as well as a broad band emission located at about 410nm. All the three emissions form a white light with CIE chromaticity coordinates x=0.3874, y=0.3760 and the color temperature is 4000 K under 254 nm excitation. It indicated that this phosphor is a promising new luminescent material for practice application.     

Boron‐Cluster‐Enhanced Ultralong Organic Phosphorescence

Although carborane‐based luminescent materials have been studied for years, no persistent phosphor has been reported so far. Herein, we describe boron‐cluster‐based persistent phosphors obtained by linking a σ‐aromatic carboranyl cage to the π system of a carbazolyl group. The carboranes were found to promote intersystem crossing from a singlet to a triplet state. The rigid boron cluster was able to stabilize the ultralong triplet excitons through multiple nonclassical hydrogen bonds, such as B?H???π interactions, thus leading to a long lifetime of up to 0.666 s and an absolute phosphorescence quantum yield of 7.1 %, which is outstanding for an organic phosphor without heavy atoms. These phosphors can be excited by visible light and show dynamic emission behavior, including thermochromism and mechanochromism. This study demonstrates that non‐metal/heavy‐atom boron clusters can be used to develop multifunctional high‐performance phosphors for potential applications.