Enhancement Of Red Emission Research Articles

Red emission enhancement in BaYF5:Eu3+ phosphor nanoparticles by Bi3+ co-doping.

Herein, we report the photoluminescence properties of Bi3+-sensitized BaYF5:10 mol%Eu3+ nanoparticles. The emission spectra feature Eu3+ peaks corresponding to transitions from the 5D0 excited to 7FJ (J = 1, 2, 3, 4) lower levels with two dominant emissions positioned in the orange-red (∼ 592 nm, 5D0 → 7F1) and deep-red (∼ 697 nm, 5D0 → 7F4) regions. Upon 265 nm excitation, the emission intensity increases with an increase of Bi3+ concentration up to 20 mol%. Due to the energy transfer from Bi3+ to Eu3+ ions, the integrated intensity of Eu3+ emission in the Bi3+ co-doped BaYF5:10 mol%Eu3+ is 216% stronger than in the Bi3+-free sample. Our findings demonstrated that BaYF5:Eu,Bi has potential in plant lighting technology due to strong emission in red and deep-red spectral areas.

Dual-State Red-Emitting Zinc-Based MOF Accompanied by Dual-Mode and Dual-State Detection: Color Tonality Visual Mode for the Detection of Tetracycline.

Red-emitting metal-organic frameworks (MOFs) are still mostly based on the use of lanthanides or functionalization with red fluorophores. However, production of transition-metal-based MOFs with red-emitting is scarce. This work reports on the synthesis of a novel dual-state red-emitting Zn-based MOF (denoted as UoZ-7) with the capability to detect target molecules in dual state, in solution, and as solid on paper. UoZ-7 gives strong red emission when excited in the solution and in the solid state with 365 nm ultraviolet (UV) lamp irradiation. Coordination-induced emission is the mechanism for the red emission enhancement in the MOF as a restriction of intramolecular rotation occurred to the ligand within the framework structure. UoZ-7 was successfully used for tetracycline (TC) using dual-mode detection, fluorescence-based ratiometry, and color tonality, in the dual state, in solution, and on the paper. TC molecules adsorb on the red-emitting UoZ-7 surface, and a yellow-greenish color emerges due to aggregation-induced emission between TC and UoZ-7. Concurrently, the inner filter effect diminishes the red emission of UoZ-7. The dual-mode or dual-state detection platform provides a simple and reliable fast method for the detection of TC on-site in various environmental and biomedical applications. Moreover, red-emitting UoZ-7 will have further luminescence-based biomedical applications.

Optical temperature sensing properties realized by isotropic negative thermal expansion in ScF3:Tb3+/Eu3+ phosphor ceramics

The anomalous luminescence thermal quenching performance caused by negative thermal expansion has attracted much attention due to the potential application in optical fields. However, the downshifting emissions with abnormal thermal quenching achieved by isotropic negative thermal expansion for optical temperature sensing applications are still lacking. Herein, a large enhancement of red emission and a high temperature sensing performance are realized by isotropic negative thermal expansion in ScF3:Tb3+/Eu3+ phosphors ceramics. Specially, a selectively thermal enhanced red emission of Eu3+ from 5D0→7F2 with hypersensitive transition characteristics could be obtained due to the thermal stimulated lattice distortion. Attributing to the shortening of cation spacing, the energy transfer efficiency between Tb3+ and Eu3+ is largely enhanced with the increasing of the temperature from 303 to 473 K. The enhanced energy transfer leads to that the emission of Tb3+ firstly increases and then slightly decreases, whereas the emission from Eu3+ has been largely improved. Finally, an optical temperature sensing strategy based on the fluorescence intensity ratio of the sensitizer Tb3+ (signal ions) and the activator Eu3+ (referring ions) is designed, attributing to the distinguishable luminescence response to the temperature. The obtained maximum relative sensitivity is 1.04 % K−1 (@303 K). Besides, the sensing strategy based on lifetime mode also suggests a maximum relative sensitivity of 1.00 % K−1 at 343 K. It provides a feasible strategy to obtain an optical temperature sensing material with high emission efficiency at a high temperature, which sheds light on the design of luminescence materials keeping high luminescence stability in a wide temperature range in the fields of optical temperature sensing.

Dual emissive and stable surface-capped silica based nanoparticles for white light emission

There is an emerging thrust to develop intrinsic white light emitting materials that surpass critical issues of color balance, low color-rendering index, thermal stability, and a bluish tinge displayed by conventional multi-phosphor composite materials. In particular, the luminescent Silica-based nanoparticles (NPs) have drawn attention owing to their abundance and potential applications, such as in optoelectronic devices, solar cells, and batteries. In this work, stable phenothiazine capped-SiO2 nanoparticles (PTZ capped-SiO2 NPs) with an average size of 24 ± 2 nm have been synthesized that exhibit intrinsic white light emission and have comprehensively investigated interactions of ligands on Silica core and underlying charge transfer mechanism. The dual emission has been observed, spanning over 400 to beyond 800 nm (visible to the NIR region). The emission measured at different excitation wavelengths reveals enhancement of red emission, indicating efficient CT emission, which is facilitated by strong electron donor and conformational changes capability of the phenothiazine ligand. Taking into account the excellent photo/thermal stability of PTZ capped-SiO2 NPs (up to 30 days) observed, a white LED prototype was successfully fabricated that exhibits cool white light (CIE: 0.31, 0.32) with excellent CRI (Ra) 91 and CCT 7029 K.

Enhancement mechanism of red up-conversion emission in single NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYbF<sub>4 </sub>micron core-shell structure

The construction of core-shell structure can effectively reduce the quenching effect on the surface of material and regulate ion-ion interaction, which has become one of the effective ways to enhance and regulate the spectral characteristics of rare-earth upconversion luminescent materials. In this paper, a variety of NaYbF<sub>4</sub>: 2%Er<sup>3+</sup> micron core-shell structures are constructed with the help of epitaxial growth technology, effectively improving the red up-conversion emission of Er<sup>3+</sup> ions. The prepared microcrystals with core-shell structures are of hexagonal phase microdisks, and their sizes are relatively uniform. In order to better obtain the material spectral data, a confocal microscopic spectroscopy is used to study spectral properties. Under 980 nm near-infrared laser excitation, the red emission intensity of single NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYbF<sub>4</sub>@NaYF<sub>4</sub> core-shell-shell microdisk is 4.6 times higher than that of NaYbF<sub>4</sub>:2%Er<sup>3+</sup> micron disk, and the red-to-green ratio increases from 6.3 to 8.1. Meanwhile, Ho<sup>3+</sup> ions are introduced into the NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYbF<sub>4</sub>: 2%Ho<sup>3+</sup> @NaYF<sub>4</sub> core-shell-shell microdisk, and the red emission intensity is nearly 6.7 times higher than that of single NaYbF<sub>4</sub>: 2%Er<sup>3+</sup> microdisk, and the red-to-green ratio increases from 6.3 to 9.4 through the interaction between ions. The microcrystal spectral characteristics and luminescence kinetics of different core-shell structures are studied, showing that the red emission enhancement of Er<sup>3+</sup> ions is mainly derived from the construction of different core-shell structures, which can effectively enhance the cross-relaxation between Er<sup>3+</sup> ions, the energy back transfer between Yb<sup>3+</sup> and Er<sup>3+</sup> ions, and the energy transfer from Ho<sup>3+</sup> ions to Er<sup>3+</sup> ions. The micron core-shell structures with efficient red emission in this study has great application prospects in the fields of luminescence, anti-counterfeiting and optoelectronic devices.

Plasmonic red-light-emission enhancement by honeycomb-latticed InGaN/GaN ordered fine nanocolumn arrays

By using ordered fine nanocolumns suitable for high-efficiency red-emission, emission enhancement based on surface plasmon polariton (SPP) coupling was successfully obtained for the honeycomb lattice. This lattice enables us to obtain a longer SPP resonant wavelength in the red region, which could not be attained for the triangular lattice. A 4.8-fold red-emission enhancement was achieved for the honeycomb lattice, demonstrating effective synergy between plasmonic and nanocrystalline effects within the red-emission nanocolumn system. Additionally, a 3.2-fold light-extraction enhancement was attained by changing the emission directionality by introducing plasmonic crystals (PlCs) in addition to metal reflection.

Improving the quality of red light emitting from Eu3+ by Co-doping Tb3+ in LuBa3(BO3)3

The red light emitting from phosphors activated with Eu3+ is of great significance for optimizing the comprehensive performances of white light-emitting diodes (WLEDs) for solid-state lighting. Herein, LuBa3(BO3)3:Eu3+ and LuBa3(BO3)3:Tb3+,Eu3+ phosphors are synthesized via the high temperature solid-state reaction to investigate the effects of the doping concentration of Eu3+ and the co-doping of Tb3+ on the quality of red emission from Eu3+ in the host. Under the excitation of 392 nm light, the dominant emission peak of LuBa3(BO3)3:xEu3+ gradually shifts from 593 nm to 610 nm when the doping concentration of Eu3+ is increased from 0.02 to 0.10, and the quality of red light emitting from Eu3+ in the host is found to be further improved with increasing the co-doping concentration of Tb3+, both of which are explained with the Judd-Ofelt theory. The calculated results indicate that the enhancement of red emission is attributed to the decrease of the environment symmetry of Eu3+ by increasing the concentration of Eu3+ in LuBa3(BO3)3:Eu3+ or co-doping Tb3+ ions. The color purity of the emission from LuBa3(BO3)3:0.10 Tb3+,0.10Eu3+ is 94.11%, and the luminescent intensity of the phosphor at 425 K is 69% of that at room temperature. Moreover, a WLED device with the high color rendering index of 91.1 is obtained by fabricating LuBa3(BO3)3:0.10 Tb3+,0.10Eu3+ and other phosphors with a 365 nm LED chip. The good comprehensive performances suggest that LuBa3(BO3)3:Tb3+,Eu3+ has a great application prospect as a red phosphor in the field of high-quality solid lighting.

Red emission enhancement in YVO4:Eu3+ nanoparticle by changing the complexing agent in modified sol-gel route

The complexing agent modification can realize systematically the red emission enhancement of YVO4:Eu3+ nanoparticle. Using sucrose, glucose, and arabic gum as complexing agents, Eu3+-doped YVO4 nanoparticles were synthesized by a modified sol-gel route. The crystallographic structure, morphology, and composition of samples were investigated through X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is found that changing the complexing agent can be used to improve the Eu3+ emission. Structural characterizations reveal that the YVO4:Eu3+ nanoparticle can be successfully prepared using the sucrose, glucose, and arabic gum complexing agent and that particle size is strongly influenced by them. As the complexing agent change, the size of the sample particles changes. Photoluminescence (PL) emission exhibit typical Eu3+ emission lines with the 5D0→7F2 transition dominating and varying with the complexing agents.

Control of red upconversion emission in Er3+–Yb3+– Fe3+ tri–doped biphasic calcium phosphate

This paper reports a novel red upconversion (UC) emission in Er/Yb/Fe tri-doped biphasic calcium phosphate (BCP) synthesized using a solid-state reaction method. The crystal structure of BCP was analyzed using Rietveld refinement, which confirmed the hexagonal structure of hydroxyapatite and the rhombohedral structure of beta-tricalcium phosphate with good crystallinity. The results of Rietveld refinement, Fourier-transform infrared spectroscopy, and diffuse reflectance spectroscopy revealed that the presence of Fe3+ in the host lattices strongly influenced the crystal structure of the phosphors. The phosphors showed intense red UC emission with a maximum at 660 nm upon the near-infrared excitation of a diode laser at 975 nm. Significantly, the red emission intensities of the Fe3+-doped sample were 60-times greater than those of the undoped sample. The preferential enhancement of red UC emission was due to the energy transfer from the high-energy excited state |2F7/2, 4T1g > of the Yb3+-Fe3+ dimer to the 4F9/2 state of the Er3+ ions. The UC emission mechanism was primarily estimated by the dependence of the UC spectral intensities on the laser 975 nm excitation power. The BCP: Er/Yb/Fe phosphor generating strong red UC emission could be used to develop a highly effective bioimaging tool in biomedicine.

Red upconversion emission of Er<sup>3+</sup> enhanced by building NaErF<sub>4</sub>@ NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structure

Building core-shell structures are widely used to enhance and regulate the luminescence properties of rare-earth-doped micro/nano materials. In this work, a variety of different NaErF<sub>4</sub> core-shell and core-shell-shell nanocrystals are successfully constructed based on high temperature co-precipitation method by epitaxial growth technology. The upconversion red emission intensities of Er<sup>3+</sup> ions in different core-shell structures are effectively enhanced by regulating their structures and doping ions. The experimental structures show that the constructed core-shell nanocrystals each have a hexagonal phase structure, and core-shell structure of about 40 nm. In the near infrared 980 nm laser excitation, the NaErF<sub>4</sub> core-shell nanocrystal shows a strong single-band red emission. And the single-band red emission intensity of Er<sup>3+</sup> ions is enhanced through constructing the NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structure. The experimental results show that red emission intensity of Er<sup>3+</sup> ions is about 1.4 times higher than that of the NaErF<sub>4</sub>@NaYbF<sub>4</sub> core-shell structure by constructing the NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures under 980 nm excitation, and its red/green emission intensity ratio increases from 5.4 to 6.5. Meanwhile, when NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structure recoats the NaYF<sub>4</sub> inert shell and is added with a small quantity of Tm<sup>3+</sup> ions, their red emission intensities of Er<sup>3+</sup> ions are 23.2 times and 40.3 times that of NaErF<sub>4</sub>@NaYbF<sub>4</sub> core-shell structures, and their red/green emission intensity ratios reach 7.5 and 10.2, respectively. The red emission enhancement of Er<sup>3+</sup> ions is mainly caused by bidirectional energy transfer process of high excitation energy of Yb<sup>3+</sup> ions and energy trapping center of Tm<sup>3+</sup> ions which effectively change the density of population of luminescent energy levels of Er<sup>3+</sup> ions. Furthermore, the coated NaYF<sub>4</sub> inert shell also effectively weakens the surface quenching effect of nanocrystals. The mechanisms of red enhancement in different core-shell structures are discussed based on the spectral properties, the process of interion energy transfer, and luminescence kinetics. The constructed NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYF<sub>4</sub> core-shell structures with high-efficiency red emission in this work have great potential applications in the fields of colorful anti-counterfeiting, display and biological imaging.

Structural Confinement and Energetic Matching Synergistic Effect toward a High-Energy Transfer Efficiency and a Significant Red Emission Enhancement in a Eu2+,Ln3+ Co-doped Sr9LiMn(PO4)7 Whitlockite Phosphor.

Despite an encouraging progress, Mn2+-activated red phosphors suffer from an insufficient emission intensity and a bad color purity. Thus, it is necessary to find a new strategy to realize a bright red emission through highly efficient Mn2+ sensitization. Herein, manipulating Eu2+-sensitized Sr9LiMn(PO4)7 (SLMP) composition by Ln3+ heterovalent substitution is proved to be able to substantially gain a tremendous Mn2+ emission enhancement and result in a dominant red Mn2+ emission. It is found that the emission enhancement ratio is proportional to the order of lanthanide contraction. Notably, Tb3+ doping realizes a 427-fold rise in the integrated emission intensity compared with the SLMP host, which is close to the theoretical maximum of 500. An underlying mechanism for Mn2+ red emission enhancement is proposed, which is attributed to a high-energy transfer probability from Eu2+ to Mn2+ via Ln3+-induced further structural confinement plus an energetic match effect. Meanwhile, homovalent (Ca2+) substitution could precisely tailor Mn2+ emitting color from orange-red to deep red. A warm-white LED device with a low color temperature of 3394 K, a high color-rendering index of 90.2, and suitable CIE coordinates of (0.403, 0.373) is fabricated using optimized phosphor SLMP:Eu2+, Tb3+. These results might reveal a new strategy to develop new red-emitting phosphors with a bright and highly purified red Mn2+ emission.

Morphology manipulation of NaYbF4:Er3+ nano/microstructures by hydrothermal synthesis and enhanced upconversion red emission for bioimaging

The synthesis of NaYbF4 crystals was successfully accomplished by a facile hydrothermal method. The phase and the morphology of the products were governed by reaction times, tuning the PH values and double solvents co-doping. The products with diverse morphologies, including quasi-spherical nanoparticles, hollow microtubes, microrods, nanorods, flower-like microprisms, and branch-like irregular shapes, were prepared under different external parameters. The experimental results demonstrate that the reaction time, PH value and organic additives play vital roles in the phase and morphology of the products. Photoluminescence measurements demonstrate that the relative upconversion (UC) photoluminescence intensity of as-prepared products strongly depends on the crystal phase, morphology, size, crystallinity, surface organic group, as well as surface defects. Impressively, the energy transfer mechanisms are systematically clarified, and the enhancement of red emission is ascribed to the high Yb3+ concentration. The emission colors might be finely tuned from green to orange-red. Furthermore, the luminescence decay lifetime is related to morphologies, sizes, defects, emission intensity, and Red/Green (R/G) ratio. Particularly, through simple cytotoxicity test and in vivo bioimaging, the synthesized UC red emission nanospheres have broad application prospects in the field of biochemistry.

Single red upconversion luminescence in β-Ba2ScAlO5: Yb3+/Er3+ phosphor assisted by Ce3+ ions

Recent decades have witnessed an explosion in research devoted to pure upconversion (UC) red emission attractive for bioimaging and anti-counterfeiting. Single-band red UC emission of Er3+ has been implemented in the new β-Ba2ScAlO5: Yb3+/Er3+ phosphor assisted by Ce3+. The red to green integrated intensity ratio reaches up to 430.9. Doping of Ce3+ ions leads to large cross-relaxation probabilities between Er3+ and Ce3+ ions when excited at 980 nm near infrared laser, resulting in suppressing the green emission and enhancing the red emitting level of Er3+. The optimal doping concentration of Ce3+ ions is 0.008 in β-Ba2ScAlO5: Yb3+/Er3+ sample, and a 4.1-fold red emission intensity enhancement was achieved than that of β-Ba2ScAlO5: Yb3+/Er3+ sample without Ce3+ ions. The possible upconversion luminescence (UCL) mechanism is investigated according to absorption spectrum, excitation spectrum, photoluminescence spectrum and upconversion emission lifetime decay spectrum of Yb3+/Er3+/Ce3+ co-doped β-Ba2ScAlO5, which was concluded that the 5d-4f energy transfer and large cross-relaxation probabilities between Er3+ and Ce3+ ions to achieve enhancement of red emission and the super-high ratio of red to green UCL emission integrated intensity. This work can pave a perspective way to obtain new phosphor with single UC red emission for applications in a variety of the fields.

Enhancement of Red Upconversion Emission of ZnS: Er3+/Yb3+ Powders Synthesized via Solid Phase Reaction Method by Introducing Metal Fluoride

AbstractZnS: Er3+/Yb3+ powders were synthesized by a common solid phase reaction method with NaF, CaF2, LiF, AlF3 and MgF2 as dopant. The enhancement mechanisms of different metal fluorides (NaF, CaF2, LiF, AlF3 and MgF2) and concentrations (0 wt% ∼9 wt %) on structure, morphology and optical properties of ZnS: Er3+/Yb3+ powders were investigated systematically. The results revealed that as synthesized ZnS: Er3+/Yb3+ powders are main exhibited as wurtzite phase, the lattice constant, unit cell volume and lattice strain increase with metal fluoride codoping, which indicates the increase of resultant distortion. As synthesized ZnS: Er3+/Yb3+ powders have an intense red upconversion emission centered at 663 nm and a weak green upconversion emission centered at 567 nm under the excitation of a 980 nm laser diode. Compared with ZnS: Er3+/Yb3+ powders synthesized without metal fluoride, the upconversion emission intensities of ZnS: Er3+/Yb3+ powders synthesized with LiF, NaF, MgF2, AlF3 and CaF enhance ∼12 times, ∼9 times, ∼5 times, ∼3 times and ∼3 times, respectively. The strong red upconversion properties make the ZnS: Er3+/Yb3+ powders synthesized with metal fluoride a potential application in the field of light emitting diodes.

Enhancement of red upconversion emission intensity of Ho3+ ions in NaLuF4:Yb3+/Ho3+/Ce3+@NaLuF4 core–shell nanoparticles

The red upconversion emission of Ho3+ ions, in the optical window of biological tissue, exhibits excellent prospects in biological applications. This study aims to enhance the red upconversion emission intensity of Ho3+ ions in NaLuF4:20%Yb3+/2%Ho3+/12%Ce3+ nanoparticles through building different core–shell structures with different excitation wavelengths. A significantly enhanced red upconversion emission with a higher red-to-green ratio was successfully obtained in NaLuF4:20%Yb3+/2%Ho3+/12%Ce3+@NaLuF4 core–shell nanoparticles by introducing the Yb3+ and Yb3+/Nd3+ ions into the NaLuF4 shell, with enhancement of the red emission occurring when Yb3+ and Nd3+ ions in the shell transfer more excitation energy to the Ho3+ ions. Investigation of the red emission enhancement mechanism is based on spectral characteristics and lifetimes. We examined the synergistic effect of dual-wavelength co-excitation NaLuF4:20%Yb3+/2%Ho3+/12%Ce3+ @NaLuF4:10%Yb3+/15%Nd3+ core–shell nanoparticles to establish optimal excitation conditions. It is hoped that this method, using red upconversion emission core–shell nanoparticles with multi-mode excitation, can provide new ways to expand the applications of rare-earth luminescent materials in biomedicine and anti-counterfeiting.

Photooxidation-Driven Purely Organic Room-Temperature Phosphorescent Lysosome-Targeted Imaging.

The construction of host-guest-binding-induced phosphorescent supramolecular assemblies has become one of increasingly significant topics in biomaterial research. Herein, we demonstrate that the cucurbit[8]uril host can induce the anthracene-conjugated bromophenylpyridinium guest to form a linear supramolecular assembly, thus facilitating the enhancement of red fluorescence emission by the host-stabilized charge-transfer interactions. When the anthryl group is photo-oxidized to anthraquinone, the obtained linear nanoconstructs can be readily converted into the homoternary inclusion complex, accompanied by the emergence of strong green phosphorescence in aqueous solution. More intriguingly, dual organelle-targeted imaging abilities have been also distinctively achieved in nuclei and lysosomes after undergoing photochemical reaction upon UV irradiation. This photooxidation-driven purely organic room-temperature phosphorescence provides a convenient and feasible strategy for supramolecular organelle identification to track specific biospecies and physiological events in the living cells.

The enhanced up-conversion green by Yb-Mn dimer in NaBiF4:Yb3+/Er3+/Mn2+ for optical fiber temperature sensor

Through doping Mn2+ into the NaBiF4:Yb3+/Er3+, it can be achieved that NaBiF4 :Yb3+/Er3+/Mn2+ possess superior temperature sensing performance and application in temperature optical fiber sensing on the premise of enhancing the green emission upon the 980 nm excitation. The effect of Mn2+ content on the phase and luminescence of NaBiF4:Yb3+/Er3+/Mn2+ is investigated by X-ray diffraction (XRD) and fluorescence spectrophotometer characterization. The up-conversion (UC) green emission intensity is enhanced by 3 times by Mn2+ doping. The Yb3+-Mn2+ dimer is introduced to clarify the mechanism of UC red and green emission enhancement, where involved in is three-photon process. Moreover, the optical thermometric behaviors of the synthetic compounds are analyzed according to the fact that Er3+ processes a couple of green emission levels 2H11/2 and 4S3/2, and the maximum Sa (absolute sensor sensitivity) reaches 0.00559 K−1. The preliminary design and application of NaBiF4:Yb3+/Er3+/Mn2+ as a probe in the temperature optical fiber sensor has been carried out, suggesting that NaBiF4: Yb3+/Er3+/Mn2+ is expected to be a kind of promising material for non-contact optical thermometer.

Upconversion enhancement of red-emitting Er3+/Yb3+ with silver nanoparticles codoped tungsten tellurite glasses

The glasses system TeO2-WO3-Li2O containing Er-Yb and Ag nanoparticle (TWLEYA) has been prepared by the metal quenching technique. In the presence of Ag2O in these glasses, silver nanoparticles (AgNPs) is obtained by mean of reheat-treated 12h duration. XRD measurements of the heat-treated glasses confirm the growth of the crystalline phase and glass-ceramic nature of samples. Uv-Vis absorption spectrum demonstrated the characteristic transition of Yb3+ and Er3+ ions with local surface plasmon resonance absorption band of AgNPs arisen at 525nm and 650 nm. For heat-treated TWLEYA glasses under 980nm excitation show two main upconversion transition peak at 548nm and 657nm emerging from 4S3/2 and 4F9/2 states of the Er3+ ions, respectively. All AgNPs doped TWLEYA sample produced huge green contrary to red emission by 980 nm pumping. However, the red emission enhanced by two-fold factor has been measured for 0.7mol% of AgNPs in TWLEYA sample. For these glasses, red emission enhancement is gained by local field proximity of the Ag NPs. Further contribution of optimum 0.7 mol% AgNPs in TWLEYA glass and its emission enhancement of possible energy transfer from AgNPs to Er-Yb has been analyzed.

Tuning electroluminescence performance in Pr-doped piezoelectric bulk ceramics and composites

Alternating current electroluminescence (ACEL) shows great potential in lighting, display and intelligent skin. Herein, the ACEL properties of Pr3+-doped Ba0·85Ca0·15Ti0·90Zr0·10O3 ceramic and its PDMS-based composite have been investigated. Intense red EL emission was obtained in the ceramic sample whereas blue EL emission of Pr3+ was observed for the first time in the composite counterpart. The red EL emission should be attributed to the impact of hot electrons driven by the large piezoelectric electric field. Owing to the cross-relaxations through the 4f5d levels and Pr-to-metal charge transfer state, the 3PJ emissions were completely quenched, and thus leading to an enhancement in red emission. However, external E field induced a large local piezoelectric deformation of the ceramic particles embedded in the PDMS matrix, which in turn caused a bending of CB and then a downwards shift of the 4f5d levels from the CB. Hence the cross-relaxations were hindered, and the blue EL emission was observed in the composites. The results would attract attention of functional materials studies and expand our understanding of such facile structure and oxide EL devices to facilitate their use in integral part of flexible device systems.

Effect of Li ions on structure and spectroscopic properties of NaY(WO4)2: Yb/Ho phosphor

We demonstrate the preparation of NaY(WO4)2 phosphor particles with 1 mol% Ho3+ and various Yb3+ and Li+ via solid-state reaction. The X-ray diffraction and infrared absorption spectrum results show that Yb3+ and Li+ would shrink the crystal lattice owning to their much smaller ionic radius. However, the W–O bond has been altered by Li+ due to its stronger polarizability, and thus enlarges the crystal lattice parameters when Li+ concentration is relatively high. According to the scanning electron microscope images, the mean size of Li+ doped samples distribute from 1.75 μm to 2.58 μm. The up-conversion properties are studied under 980 nm laser diode excitation. All samples demonstrate two typical emission peaks located around 544 nm and 660 nm, which are corresponding to the 5S2/5F4→5I8 and 5F5→5I8 transitions in Ho3+. Pump power law coefficients infer that both 544 nm and 660 nm emissions involves two-photon processes. Additionally, doping of Li+ would significantly increase the green and red emissions intensities, with maximum enhancement of 3.65-fold and 7.51-fold, respectively. From Judd-Ofelt theory, the increasing intensity at 544 nm might attribute to the tailoring of local symmetry around Ho3+, thus enlarging Ω2 value. For the 660 nm emission, some promoted non-radiative relaxation processes could account for its great enhancement. The prolonged fluorescence decay lifetimes would make their great enhancement well comprehended. The notable enhancement in red emission would move the color-coordinates from green region to yellow-green regions, thus making it a novel candidate for multi-color materials to be further investigated.