Inorganic Phosphors Research Articles

Rare earth doped organic–inorganic hybrid polyhedral oligomeric silsesquioxane phosphors applied for flexible sheet and anti-counterfeiting

We have developed organic–inorganic hybrid polyhedral oligomeric silsequioxane (POSS) type monomer ligand 2,6-pyridinediamine-bis-propanylheptaisobutyl POSS (PDC-POSS) and synthesized rare earth (RE =Eu3+) doped hybrid complex PDC-POSS phosphors. The PDC-POSS precursor was prepared using (3-aminopropyl)heptaisobutyl POSS, 2,6-pyridinedicarboxylic acid chloride (PDC) as the host material, and then coordinated with RE3+ using europium nitrate regents to synthesize PDC-POSS:Eu3+ phosphors. The photoluminescence (PL) spectra of the PDC-POSS:Eu3+ hybrid phosphors were detected at 592, 616, 649, 693 nm under UV light (λ= 288 nm) excitation. In addition, the synthesized hybrid phosphors showed red light emission under UV light. The phosphors were demonstrated on a flexible sheet that could be applied for red emitting LEDs, and for anti-counterfeiting, which requires the film to remain hidden and identifiable only by UV light.

NUV-pumped luminescence of thermally stable samarium-activated alkali metal borophosphate phosphor

Exploring outstanding rare-earth activated inorganic phosphors with good thermostability has always been a research focus for high-power white light-emitting diodes (LEDs). In this study, we report a Sm3+-activated KNa4B2P3O13 (KNBP) powder phase. Its particle morphology, photoluminescence properties, concentration quenching mechanism, thermal quenching mechanism, and chromatic properties are demonstrated. Upon the near-ultraviolet (NUV) irradiation of 402 nm, the powder phase exhibits orange-red visible luminescence performance, originating from typical 4G5/2→6HJ/2 (J = 5, 7, 9) transitions of Sm3+. Importantly, the photoluminescence performance has good thermostability, low correlated color temperature (CCT), and high color purity (CP), indicating its promising application in the NUV-pumped warm white LEDs.

Ca[B8 O11 (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[B8 O11 (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 (Eg ) 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.

Molten salt synthesis and luminescence performance of the Ce3+/Eu2+ doped Sr3Y2Ge3O12 phosphors

The Ce3+ and/or Eu2+ doped inorganic phosphors with the broad excitation bands and efficient visible emission play the important roles in the light emitting diodes. Herein, we synthesized the Ce3+/Eu2+ doped Sr3Y2Ge3O12 phosphors via a molten salt method under a reducing atmosphere. The phosphors were investigated by the X-ray diffraction, scanning electron microscopy, transmission electron microscopy and fluorescence spectrophotometer. The thermal stability of the Sr2.91Ce0.03Eu0.06Y2Ge3O12 phosphor was evaluated in 300–500 K at a temperature interval of 25 K. Upon the excitation at 450 nm, the Sr2.97Ce0.03Y2Ge3O12 and Sr2.97Eu0.03Y2Ge3O12 phosphors emit green and yellow-red light, respectively. The energy transfer process from Ce3+ to Eu2+ occurs in Ce3+/Eu2+ codoped Sr3Y2Ge3O12 phosphors, which results in the tunable luminescence.

Aluminate-Based Nanostructured Luminescent Materials: Design of Processing and Functional Properties.

Interest in luminescent materials has been continuously growing for several decades, looking for the development of new systems with optimized optical properties. Nowadays, research has been focused on the development of materials that satisfy specific market requirements in optoelectronics, radioelectronics, aerospace, bio-sensing, pigment applications, etc. Despite the fact that several efforts have made in the synthesis of organic luminescent materials, their poor stability under light exposure limits their use. Hence, luminescent materials based on inorganic phosphors are considered a mature topic. Within this subject, glass, glass-ceramics and ceramics have had great technological relevance, depending on the final applications. Supposing that luminescent materials are able to withstand high temperatures, have a high strength and, simultaneously, possess high stability, ceramics may be considered promising candidates to demonstrate required performance. In an ongoing effort to find a suitable synthesis method for their processing, some routes to develop nanostructured luminescent materials are addressed in this review paper. Several ceramic families that show luminescence have been intensively studied in the last few decades. Here, we demonstrate the synthesis of particles based on aluminate using the methods of sol-gel or molten salts and the production of thin films using screen printing assisted by a molten salt flux. The goal of this review is to identify potential methods to tailor the micro-nanostructure and to tune both the emission and excitation properties, focusing on emerging strategies that can be easily transferred to an industrial scale. Major challenges, opportunities, and directions of future research are specified.

Luminescence investigation of Lu2MgAl4SiO12:Ce3+ and Ca2+ substituted Lu2MgAl4SiO12:Ce3+ phosphors

Inorganic phosphors with the broad excitation bands and efficient visible emission are important to fabricate lighting emitting diodes. Herein, we fabricated the Lu2MgAl4SiO12:Ce3+ and Ca substituted Lu2MgAl4SiO12:Ce3+ phosphors by a sol-gel approach. Their characteristics were investigated by X-ray diffraction, scanning electron microscopy and fluorescence spectrophotometer. The thermal stabilities of Lu1.95Ce0.05MgAl4SiO12 and Lu1.95Ce0.05Mg0.25Ca0.75Al4SiO12 were evaluated in the temperature rage of 30–230 °C. In addition, the mechanisms of concentration quenching and thermal stability were discussed. Upon the excitation at 435 nm, Lu2−xCexMgAl4SiO12 and Lu1.95Ce0.05Mg1−yCayAl4SiO12 phosphors show emission bands with changing peak wavelength by reason of the changing crystal field splitting with the changing Ce3+ and Ca2+ concentrations. Meanwhile, the substitution of Ca2+ to Mg2+ leads to the enhancements of thermal stability of luminescence.

Machine learning aids discovery of new, improved inorganic phosphors

Machine learning aids discovery of new, improved inorganic phosphors

A terbium-sensitized Eu3+-activated deep-red-emitting phosphor for plant growth LED application

Traditional Eu3+-activated inorganic phosphors are habitually used for general lighting and display because they generally emit either intense orange (5D0-7F1) or red (5D0-7F2) light whose wavelength is shorter than 630 nm. However, less known nor focused is that Eu3+ at sites with specific symmetry can intensify its 5D0-7F4 transition, enabling Eu3+ itself to emit deep red light (>700 nm) even stronger than the above orange and red ones. Herein, a novel Eu3+-activated phosphor, Ca2TbSn2Al3O12:Eu3+, is developed from the garnet structure. Differing from other Eu3+-activated phosphors, the 5D0-7F4 transition of Eu3+ in the host is dominant and the orange, red and deep red emissions are balanced. Such special features of Eu3+ luminescence mainly meet the need of phytochromes (PFR and PR) in plants. Additionally, bridge style energy transfer from the host composition element Tb3+ to the activator Eu3+ can be observed. It is found the Tb3+-Eu3+ energy transfer here takes through the mechanism of dipole-dipole interaction and the simulation on decay curve of Eu3+ upon Tb3+ excitation, for the first time, confirms the existence of terbium bridge energy transfer. For the Ca2Tb0.60Sn2Al3O12:0.40Eu3+, the energy transfer efficiency is as high as 94.4% and the emission color is totally red. Thermal quenching studies reveal that the emission intensity of the phosphor at 425 K sustains 80% of its initial intensity at room temperature. By fabricating the phosphor with a 380 nm LED chip, a plant-growth LED device can be obtained.

Silicate-based persistent phosphors

Eu2+-doped alkaline-earth silicates are the second most studied group of persistent luminescent inorganic phosphors after aluminates, such as SrAl2O4. Silicates are comparable with the aluminates in terms of chemical stability, high quantum efficiency and large band gap, but offer advantages including better water resistance and lower calcination temperature. Their applications range from traditional uses such as traffic signs, tile decoration or fluorescent lamps to more advanced ones such as solar cells, LEDs or in the medical field.The highest persistence has been found in (Ca,Sr,Ba)3MgSi2O8: Eu2+, Dy3+, Ba4(Si3O8)2: Eu2+, Dy3+ or Sr2MgSi2O7: Eu2+, Dy3+. Various synthesis routes have been employed to obtain crystals of these phases, such as sol-gel, hydrothermal and combustion synthesis and, more commonly, solid-state reaction. The preparation of silicate phosphors from glass crystallization has not yet been widely explored. Here, we review the progress made in the research of these inorganic crystalline phosphors, the proposed persistent luminescence mechanisms taking place and the different preparation methods employed to date, with special attention paid to the Sr2MgSi2O7: Eu2+, Dy3+ phase due to its long afterglow emission.

Naturally Derived Organic Dyes for LED Lightings of High Color Rendering and Fidelity Index

AbstractLight‐emitting diodes (LEDs) are a lighting technology with a huge and ascending market. Typically, LED backlights are often paired with inorganic phosphors made from rare‐earth elements (REEs) to tune the emission lineshapes for different applications. However, REE production is a resource‐intensive process with many negative environmental impacts. Herein organic hybrid LEDs are developed using organic dyes synthesized from an abundant and non‐toxic natural product (theobromine) to replace REE phosphors. The resulted hybrid LED generates continuous emission from 400–740 nm, resulting in a high color rendering index (the current industry standard) of 90 and a color fidelity index (the most advanced and comprehensive standard) of 92, challenging commercial LEDs based on REE phosphors. In addition, the light‐converting composite is made from 99 wt% SBS, an inexpensive industrial polymer, and 1 wt% theobromine dyes, reducing the cost of the light converter to ¢1.30 for a 1 W LED, compared to approximately ¢ 19.2 of commercial products. The light converting efficiency of the dye‐SBS composite is 82%. Excited state kinetics experiments are also conducted to provide guidance to further increase the light‐converting efficiency of the theobromine dyes while maintaining excellent color rendering and fidelity.

A review: X-ray excited luminescence of gadolinium based optoelectronic phosphors.

X-ray excited fluorescence tomography is an emerging field in the application of bio-imaging and computer tomography. Some rare-earth doped inorganic phosphors like gadolinium oxide (Gd2 O3 ), yttrium oxide (Y2 O3 ), zinc tungstate (ZnWO4 ), cesium fluoride (CsF), barium fluorochloride (BaFCl), lanthanum oxybromide (LaOBr) are shown outstanding applications for X-ray excited phosphors. Gadolinium (Gd)-based inorganic phosphors show extraordinary applications in the field of X-ray chromatography and computer chromatography. In this review article, we discussed the general information about X-ray excited luminescence (XEL) phosphor. Further, we discussed importance, synthesis, structural and photoluminescence (PL) properties of rare-earth (Europium (Eu)) doped Gd2 O3 . To elaborate the scope of the review, we have discussed synthesis, structural and optical properties of lithium (Li) doped Gd2 O3 :Eu. At the end of the review, synthesis, structural and optical properties of Eu doped lutetium oxide (Lu2 O3 ) have been discussed and the results compared with Eu doped Gd2 O3 . The comparison provided the understanding of structural and optical peak position of host and the dopant (Eu).

Combinations of Superior Inorganic Phosphors for Level‐Tunable Information Hiding and Encoding

AbstractInorganic photoluminescence (PL) phosphors (including upconversion (UC), down‐shifting (DS), and persistent (PersL) materials) with tunable outputs, high quantum yields (QYs), and excellent photostability have attracted tremendous attention in advanced information hiding and encoding (IHE). The three kinds of phosphors endow security patterns in different IHE levels owing to their unique optical features. For security applications, it is very necessary to review how to boost optical performance and achieve multi‐level anti‐counterfeiting. Herein, diversely pivotal approaches on the achievement of multicolor emissions, high QYs, and excellent photostability are summarized. Full learning of these methods is promising to design superior inorganic phosphors. Based on the appealing optical properties of inorganic PL materials, a progressively improved IHE level is revealed by using unitary inorganic PL material, the couples of UCL, DS, and PersL, and further combinations together with external stimuli. This review not only deepens an understanding of designing high‐performance inorganic PL phosphors, but also gets inside into the construction of high‐performance IHE.

Design principles for achieving red emission in Eu2+/Eu3+ doped inorganic solids

Rare earth (RE) ions activated inorganic phosphors with multi-color emissions have received considerable attention because of their emerging applications in solid-state lighting, backlight displays, lasers, biomedical imaging, and so on. This tutorial review concerns the design principles for Eu2+ and Eu3+ activated red-emitting inorganic solids and highlights the influencing factors on the luminescence performance. Based on the recent advances in structural design of inorganic RE phosphors, we proposed several design principles for achieving red emission in Eu2+/Eu3+ ions doped solid-state materials. On the one hand, for the realization of red emission from Eu2+ ion, the used strategies include the following: (1) designed synthesis of new Eu2+-doped nitride or sulfide phosphors, (2) anionic substitution achieves large centroid shift, (3) Eu2+ occupies polyhedrons with small coordination numbers to obtain large ɛcfs, (4) doping concentration controls the distribution of Eu2+ ions, (5) mixed ligands induce large ΔS, and (6) doping Eu2+ in nitrides with UCr4C4-type structure to achieve narrow-band red emission. On the other hand, for the red emission originating from a Eu3+ ion, the design principles are listed as follows: (i) designed synthesis of Eu3+-doped phosphors with small CT energy, (ii) realization of low excitation energy by doping sensitizer ions, (iii) Eu3+ luminescence enhancement by charge compensation, and (iv) occupation of unsymmetrical sites to maintain high color purity of Eu3+. Finally, we discuss and look at the future opportunities for Eu2+/Eu3+ activated red phosphors.

Segregation Engineering in MgO Nanoparticle-Derived Ceramics: The Impact of Calcium and Barium Admixtures on the Microstructure and Light Emission Properties.

Nanostructured segregates of alkaline earth oxides exhibit bright photoluminescence emission and great potential as components of earth-abundant inorganic phosphors. We evaluated segregation engineering of Ca2+- and Ba2+-admixtures in sintered MgO nanocube-derived compacts. Compaction and sintering transform the nanoparticle agglomerates into ceramics with residual porosities of Φ = 24–28%. Size mismatch drives admixture segregation into the intergranular region, where they form thin metal oxide films and inclusions decorating grain boundaries and pores. An important trend in the median grain size evolution of the sintered bodies with dCa(10 at. %) = 90 nm < dBa(1 at. %) = 160 nm < dMgO = 250 nm ∼ dCa(1 at. %) = 280 nm < dBa(10 at. %) = 870 nm is rationalized by segregation and interface energies, barriers for ion diffusion, admixture concentration, and the increasing surface basicity of the grains during processing. We outline the potential of admixtures on interface engineering in MgO nanocrystal-derived ceramics and demonstrate that in the sintered compacts, the photoluminescence emission originating from the grain surfaces is retained. Interior parts of the ceramic, which are accessible to molecules from the gas phase, contribute with oxygen partial pressure-dependent intensities to light emission.

Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors.

Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screening of different compositions. The rapid screening allows for fast material investigation, whereas the benefits of enhanced homogeneity include improvement in the optical properties such as quantum yields and storage capacity.

Polymer-Laminated Ti3C2TX MXene Electrodes for Transparent and Flexible Field-Driven Electronics.

MXenes (Ti3C2TX) are two-dimensional transition-metal carbides and carbonitrides with high conductivity and optical transparency. However, transparent MXene electrodes with high environmental stability suitable for various flexible organic electronic devices have rarely been demonstrated. By laminating a thin polymer film onto a solution-processed MXene layer to protect the MXene film from harsh environmental conditions, we present transparent and flexible MXene electronic devices. A thin polymer layer spin-coated onto a transparent MXene electrode provides environmental stability even under air exposure longer than 7 d at high temperatures (up to 70 °C) and humidity levels (up to 50%) without degrading the transparency of the electrode. The resulting polymer-laminated (PL) MXene electrode facilitates the development of a variety of field-driven photoelectronic devices by exploiting the electric field exerted between the MXene layer and the counter electrode through the insulating polymer. Field-induced electroluminescent displays, based on both organic and inorganic phosphors, with PL-MXene electrodes are demonstrated with high transparency and mechanical flexibility. Furthermore, our PL-MXene electrode exhibits high versatility through successful implementation in capacitive-type pressure sensors and triboelectric nanogenerators, resulting in field-driven sensing and energy harvesting electronic devices with excellent operation reliability.

Surface functionalized inorganic phosphor by grafting organic antenna for long term preservation of latent fingerprints and data-security applications

Creative advancements are enormously sought for the advanced forensic and data security in modern era. Herein, fabrication of Bovine Serum Albumin (BSA) functionalized Gd2O3:Eu3+ (5 mol %) nanopowders dispersed in a poly(vinyl alcohol) (PVA) matrix for long term preservation and visualization of latent fingerprints, as well as printing. Efficient intramolecular energy transfers from coordinated ligand to the doped Eu3+ ions, called the antenna effect was precisely organized by grafting organic molecule, resultant to an enhanced photoluminescence emission. On this basis, the masking of PVA/Gd2O3:Eu3+ (5 mol %)@BSA solution on a latent fingerprints results a flexible transparent film; a highly stable fingerprint images with well-defined ridge characteristics was developed on the film, which enabling personal individualization. Interestingly, the followed latent fingerprints development technique was non-destructive and stored long duration up to 1 year on filtrating and non-filtrating surfaces. The same mechanism was also validated by utilized for application of PVA/Gd2O3:Eu3+ (5 mol %)@BSA nanocomposites in dip pen and intaglio printing. Hence, the prepared nanocomposites signify an competent method towards long preservative fingerprints as well as great performance for data security operations. This work endorses a prospective paradigm for luminescence enhancement and its applications in advanced forensic science.

Endowing Phosphor Materials with Long‐Afterglow Circularly Polarized Phosphorescence via Ball Milling

AbstractCircularly polarized luminescent (CPL) materials have emerged as new advanced optical and photonic materials. While many efforts have been devoted to the organic CPL materials, it still remains a challenge to fabricate CPL active inorganic materials due to the difficulty in the introduction of the chiral units. Here, a simple approach for achieving CPL active inorganic persistent phosphor materials is reported. By modifying the inorganic persistent phosphor materials with enantiomeric cysteine via ball milling, the inorganic circularly polarized phosphorescence (CPP) materials with long afterglow characteristics are fabricated. Moreover, the circular polarization of the obtained phosphorescent materials can be controlled by the molecular chirality of the cysteine. The dissymmetry factor (glum) of the CPP materials can be up to 10−2. It is envisaged that this approach will afford a new insight into the designing of the inorganic functional chiral phosphorescent materials.

Enhancement of photoluminescence emission of Gd3+ activated borate phosphors for phototherapy lamps: A review

In this review paper, we discuss about photoluminescence emission of Gd3+ in various inorganic phosphors. Narrow band UVB (NB-UVB) emission of Gd 3+ in 312-315 nm is well sought after in medical field to treat photo-responsive diseases like atopic dermatitis, vitiligo, psoriasis, etc. However, this 4f-4f, 6Pj → 8S7/2 intra-configurational transition of Gd3+ is weak and hence needs to be sensitized. Suitable sensitizers like Bi3+, Pr3+ are found to enhance the PL emission of Gd3+. Such phosphors with sensitized Gd3+ emission is highly suitable for phototherapy lamps.

Inside Back Cover: Ultralong Room‐Temperature Phosphorescence from Boric Acid (Angew. Chem. Int. Ed. 17/2021)

The impressive and unexpected long-lived room-temperature phosphorescence of boric acid (H3BO3) is unveiled by Peng Wu and co-workers in their Research Article on page 9500. Unlike traditional metallic inorganic or aromatic organic phosphors, the phosphorescence originates from the weak conjugation of lone pair electrons from O atoms. The vacant pz orbital of B and the regular arrangement in the crystalline state with layer-like packing through abundant hydrogen bonding are found to contribute to the long-lived emission.