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Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

Nine lanthanide-organic frameworks [Ln(L)1.5(H2O)3] (1-Ce, 2-Dy, 3-Eu, 4-Gd, 5-Ho, 6-Nd, 7-Pr, 8-Sm, and 9-Tb; H2L = 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoic acid) have been synthesized under solvothermal conditions. Single-crystal X-ray diffraction analyses show that compounds 1-9 are isomorphic, in which each Ln atom is linked by L ligands to form a 3D framework with an unprecedented 4,4,6-connected topology. All these compounds have excellent solvent stability and can remain stable in boiling water for up to a week. Moreover, these compounds exhibit metal-dependent luminescence and magnetic properties. 3-Eu and 9-Tb exhibit relatively good fluorescence properties, 4-Gd shows ferromagnetic coupling, and the other compounds present antiferromagnetic coupling. [ABSTRACT FROM AUTHOR]

Overlapping between the quantum-well structure and p–n junction plays an important role in the development of high-efficiency GaAs-based light-emitting diodes (LEDs). In this work, we apply p–n junction engineering to study electro-photoluminescence spectra under open-circuit, forward voltage, and reverse voltage conditions. Through modifying the doping of p-layer or n-layer, luminescent characteristics are apparently improved as a result of the more effective overlapping of the quantum-well structure and p–n junction caused by energy band modification, with the more balanced carrier and stronger confinement in quantum wells. Furthermore, the electroluminescence spectra of all LEDs studied herein are consistent with the photoluminescence results. This work provides an explicit way to tune p- and n-doping to increase emission efficiency, which is important for research and industrial applications. [ABSTRACT FROM AUTHOR]

The development of circularly polarized electroluminescence (CPEL) is currently hampered by the high difficulty and cost in the syntheses of suitable chiral materials and the notorious chirality diminishment issue in electrical devices. Herein, diastereomeric IrIII and RuII complexes with chiral (±)‐camphorsulfonate counteranions are readily synthesized and used as the active materials in circularly polarized light‐emitting electrochemical cells to generate promising CPELs. The addition of the chiral ionic liquid (±)‐1‐butyl‐3‐methylimidazole camphorsulfonate into the active layer significantly improves the device performance and the electroluminescence dissymmetry factors (≈10−3), in stark contrast to the very weak circularly polarized photoluminescence of the spin‐coated films of these diastereomeric complexes. Control experiments with enantiopure IrIII complexes suggest that the chiral anions play a dominant role in the electrically‐induced amplification of CPELs. [ABSTRACT FROM AUTHOR]

Nano‐ and micromaterials with anisotropic photoluminescence and photon transport have widespread application prospects in quantum optics, optoelectronics, and displays. But the nature of the polarization information of the out‐coupled light, with respect to that of the source luminescence, has never been explored in active optical‐waveguiding organic crystals. Herein, three different modes (selective, anisotropic, and consistent) of polarized‐photon out‐coupling are proposed and successfully implemented in a set of 2D organic microcrystals with highly linearly‐polarized luminescence. It is found that the polarization direction and degree of the luminescence out‐coupled through different waveguiding channels can either be essentially retained or distinctly changed with respect to those of the original luminescence, depending on the molecular arrangement and the orientation of transition dipole moments of the crystal. This work demonstrates the promising potential of 2D emissive microcrystals in multi‐channel polarized photon transport. [ABSTRACT FROM AUTHOR]

A simple and general method is presented herein for the in situ preparations of circularly polarized luminescence (CPL)‐active microcrystals with a large luminescence dissymmetry factor glum, high fluorescence quantum efficiency (ΦFL), wide emission color tenability, and well‐ordered morphology. The reactions of pyridine‐containing achiral molecules 1–7 with chiral camphor sulfonic acid ((±)‐CSA) gave crystalline microplates formed by hydrogen bonding interactions between the protonated pyridinium units and the sulfonic anions. The chiral information of CSA are effectively transferred to the microcrystals by hydrogen bonding to afford full‐color CPL from deep‐blue to red with glum in the order of 10−2 and ΦFL up to 80 %. Moreover, organic microcrystals with high‐performance white CPL (ΦFL=46 %; |glum|=0.025) are achieved via the light‐harvesting energy transfer between blue and yellow emitters. [ABSTRACT FROM AUTHOR]

A green and efficient synthesis of aqueous CdTe quantum dots (QDs) embedded in inorganic salt enabled by co-precipitation is demonstrated, providing a new type of solid-state conversion material with emission colors covering green to red spectral regions. CdTe QDs were synthesized in the water phase, followed by incorporation into inorganic salt with the assistance of ethanol. Due to the protection of the tight matrix, the resulting composites exhibit good stability and processability as well as high photoluminescence properties. A white light emitting diode (WLED) applying the composites as a red color conversion layer with good luminescence properties is also fabricated, suggesting the promising application of the composites in solid-state lighting systems. [ABSTRACT FROM AUTHOR]

A novel phosphor, Mn doped LaLiTaO, was developed by solid-state reaction method. The luminescent spectra and emission efficiencies of LaLiTaO:Mn ( x = 0.001, 0.003, 0.005 and 0.01) were discussed. The effects of co-doped charge compensation ions, M = Mg, Ca, Na, were investigated, respectively. The excitation spectra indicated that LaLiTaO:Mn could be effectively excited by both NUV light and blue light. The emission spectra of the phosphor exhibit a broadband ranging from 670 to 720 nm with the maximum at about 709 nm in deep red region. The co-doping of Mg could significantly improve the luminescent properties of LaLiTaO:Mn. Thus, phosphor LaLiTaO:Mn, Mg can serve as a key component to improve color rendering of blue-chip white-LEDs. [ABSTRACT FROM AUTHOR]

A novel phenomenon about the luminescence intensification by the coupling of two phases in a complex was presented. The phosphors were synthesized through solid-state reaction and the highest luminescence was obtained by tailoring SrO and Al2O3 ratios in the SrO-Al2O3 system. The red emission originated from Mn4+, while Mn2+ was also identified from electron paramagnetic resonance spectra. The lattice vibration was observed from Raman spectra. Meanwhile, the dielectric properties were measured. The mechanism based on electromechanical coupling between Sr4Al14O25 and SrAl2O4 phases in the 3SrO · 5Al2O3 complex was proposed and discussed from the viewpoint of lattice vibrations and the dielectric field. [ABSTRACT FROM AUTHOR]

High-saturated red phosphors Mn4+-doped SrAl12O19 were prepared by solid-state reaction methods. The luminescent properties of SrAl12O19:Mn4+ were systematically investigated. The excitation spectra indicated that SrAl12O19:Mn4+ could be effectively excited by both NUV light and the blue light of LED chips. The emission spectra exhibit two sharp peaks in the deep-red region. The effects of codoping ions, M = Li+, Na+, K+, Mg2+, on the luminescent properties of SrAl12O19:Mn4+ were investigated, respectively. The results suggested that Mg2+ could significantly improve the luminescent properties of SrAl12O19:Mn4+, and the phosphor SrAl12O19:Mn4+,Mg2+ was demonstrated to be a potential candidate for high colour rendering white LEDs. CIE chromaticity diagram of different phosphors and luminescence of SrAl12O19:Mn4+,Mg2+ phosphor (a). A commercial blue LED chip coated with SrAl12O19:Mn4+,Mg2+ (b) and the luminance of SrAl12O19:Mn4+,Mg2+ excited by a 365-nm light source (c) (×: the CIE chromaticity of a blue chip LED+ YAG:Ce coated with SrAl12O19:Mn4+,Mg2+, 20 mA). [ABSTRACT FROM AUTHOR]

Abstract: Highly luminescent blue-emitting CdS/ZnS core/shell quantum dots (QDs) were synthesized in N-oleoylmorpholine by two facile steps: first, the CdS core QDs were prepared via a simple one-pot method involving a direct reaction of Cd precursor cadmium stearate and S precursor S powder in solvent N-oleoylmorpholine; second, ZnS shells were successively overcoated on CdS core through the decomposition of single molecular precursor zinc diethyldithiocarbamate. The thickness of shell was precisely tuned by controlling drip feed speed and amount of shell precursor. The obtained CdS/ZnS core/shell QDs showed the maximum photoluminescent quantum yield of 54.8% and narrow spectra bandwidth, exhibiting high monodispersity, good color purity and long fluorescent lifetimes. The CdS/ZnS core/shell QDs with tunable emission wavelength of 424–470nm were obtained by controlling the thickness of ZnS shell overgrown on different-sized CdS QDs, which are promising materials for blue light-emitting devices. [Copyright &y& Elsevier]

Abstract: High-quality CdSe quantum dots with less common zinc blende structure were prepared in non-coordinating solvent 1-octadecene, with environment-friendly N,N-dimethyl-oleoyl amide as an alternative chemical to replace trioctylphoshine for Se powder, oleic acid as primary capping ligands, and benzophenone as secondary ligands. The temporal evolution of the optical properties of the nanocrystals with different growth temperature was monitored. Significant redshifts occurred with the increase of the growth temperature. The sharpness of the first absorption peaks and the narrow emission band with full width at the half-maximum of about 30nm indicates that the size distribution of the resulting quantum dots is narrow. [Copyright &y& Elsevier]

Abstract: The intermediate role of Gd3+ in energy transfer to give light was investigated through spectroscopic study of Bi3+/Eu3+ doped YBO3/(Y,Gd)BO3 under VUV/UV excitation. All samples were prepared by solid-state reaction and the luminescent properties were characterized in a synchrotron radiation instrument. The results show that Gd3+ plays an intermediate “bridge” between the sensitizer of Bi3+ and the activator of Eu3+ in energy transfer in (Y,Gd)BO3:Bi3+,Eu3+ system. At the same, the mechanism for energy transfer was discussed, which is mainly through electric multipole interaction or exchange interaction. [Copyright &y& Elsevier]

Anti-counterfeiting technologies are desired to protect products far away from the violation of dummy, fake and shoddy goods. The phosphor of (Y,Gd)VO4:Bi3+,Eu3+ was synthesized for the application of this purpose. Its photoluminescence was investigated by exciting with different wavelengths at variant temperatures. Wide emission color ranged from green through yellow to orange was tuned up by tailor-ing Bi3+ and Eu3+ concentrations. The temperature dependent luminescence and wavelength selective excitation of (Y,Gd)VO4:Bi3+,Eu3+ were observed, which provide different encryptions in anti-counterfeiting. To verify the feasibility in application, two anti-counterfeiting patterns were fabricated practically and excellent performance was obtained. Moreover, the physical mechanisms for the different phenomena of luminescence were elucidated from excitation spectra combining with the configuration coordinate model. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Research on lithium compounds has attracted much attention nowadays. However, to elucidate the precise structure of lithium compounds is a challenge, especially when considering the small ions that may be transferred between the interstitial voids. Here, the discovery of reduced local symmetry (symmetry breaking) in small domains of Li2SrSiO4 is reported by employing Eu3+ as a spectroscopic probe, for which X‐ray, neutron, and electron diffraction have confirmed the average long‐range structure with the space group P3121. However, luminescence shows a lower local symmetry, as confirmed by the extended X‐ray absorption fine structure. By considering the reduced symmetry of the local structure, this work opens the door to a new class of understanding of the properties of materials. [ABSTRACT FROM AUTHOR]

A series of metal cluster-based complexes were constructed from the reaction of metal ions (Fe III , Cu II , Zn II ) and ligand (2-({2-[2-carbosybenzoy])oxy]-ethoxy}carbonyal)benzoic acid) (H 2 L) in CH 3 CH 2 OH, CH 3 OH, (C 2 H 5 ) 3 N and C 2 H 3 N. Two paddle wheel trinuclear clusters [Fe 3 ( μ 3 -O)( μ 2 -η 2 -L) 3 (CH 3 OH) 3 ]NO 3 ·C 2 H 5 OH·CH 3 OH ( 1 ) and [Fe 3 ( μ 3 -O)( μ 2 -η 2 -L) 3 (H 2 O) 3 ]NO 3 ·5CH 3 OH·H 2 O ( 2 ), one tetranuclear cluster [Cu 2 ( μ 2 -L) 2 (C 2 H 3 N) 2 ·2C 2 H 3 N] 2 ( 3 ) and one butterfly shaped dinuclear cluster [Zn 2 (μ 2 -L) 2 (C 2 H 5 OH) 2 ]·2CH 3 OH (4) were obtained. Complexes 1 , 2 , and 4 are further assembled by intermolecular hydrogen bonds to form supramolecular frameworks. In complex 3, the flexible benzoic acid ligand chelates with two Cu II , which induces a decrease of Cu Cu intermetallic separation (rang from 2.644 to 2.657 Å). The structures of the complexes are characterized by elemental analyses, Infrared spectroscopy (IR spectroscopy), thermal gravimetry (TG) analyses, single crystal X-ray diffraction and powder X-ray diffraction techniques (PXRD), and high resolution mass spectra (HRMS). The luminescent properties of the clusters 1 – 4 are also studied, the results show that the cluster 4 exhibits blue fluorescence at room temperature. [ABSTRACT FROM AUTHOR]

A kind of interesting luminescence phenomenon from vacuum-dielectric interface under high electric field is presented in this Letter. It is visible, steady, and continuous, occurring before or accompanied with flashover across dielectric, which is quite different from general electroluminescence from insulator surface reported before. By investigating its optical and electrical characteristics, we consider it as cathode-like luminescence, which is initialized by the field electron emission from cathode triple junction and finally generated by the process of radiative recombination due to the self-stabilizing secondary electron emission and collision on insulator surface. [ABSTRACT FROM AUTHOR]

Abstract: An orange phosphor Sr3SiO5:Eu2+ was synthesized by high temperature solid state reaction. The coexisted phase Sr2SiO4:Eu2+ tended to compromise the whole luminescent properties. Sr2SiO4:Eu2+ was formed as a result of the decomposition of Sr3SiO5:Eu2+ during the cooling process, which emitted green light at about 560nm. Furthermore, the decomposition degree of Sr3SiO5:Eu2+ phase was related to the temperature. Microstructure analysis suggested that slight stoichiometric excess of SrO in the raw materials was able to suppress the decomposition of Sr3SiO5:Eu2+, thus leading to enhanced emission intensity. A new viewpoint was proposed to explain the mechanism of decomposition in the synthesis process of Sr3SiO5:Eu2+. [Copyright &y& Elsevier]

• Visible emission band from 500 to 750 nm was observed from Cu2+ in BaGa 2 O 4. • BaGa 2 O 4 :Cu showed highly temperature- & excitation-dependent emission peak position. • BaGa 2 O 4 :Cu exhibited rare reported yellow persistent luminescence more than 12 h. In the field of solid-state luminescence, Cu2+ has long been widely acknowledged for its capacity to emit infrared light. However, the occurrence of visible emission from Cu2+ ions had been infrequently observed and reported. In this study, we made an intriguing discovery by examining the behavior of Cu2+ within an irregular coordination environment of Ba in BaGa 2 O 4. When excited by UV light, Cu2+ unexpectedly gave a vibrant yellow–red emission, covering a wavelength range spanning from 500 to 750 nm. More noteworthy, by simply manipulating the excitation wavelength or adjusting the temperature, the peak wavelength of the emission could be effectively tuned from approximately 600 to 660 nm, which could be attributed to the luminescence nature of the charge transfer (CT) between O2− and Cu2+. Moreover, the phosphor material displayed a remarkable persistent luminescence (PerL) lasting up to 12 h after UV light excitation. Through thermoluminescence (TL) measurements and first-principle calculations, we found that the intrinsic defects, such as vacancies of oxygen and gallium (V O and V Ga ″), played important roles for the PerL phenomena. These findings highlighted the exceptional tunability and PerL properties of BaGa 2 O 4 :Cu2+. Our study provided a new potential guideline for the design of Cu2+-activated phosphors in visible region, and opened up new avenues for the research in related functional luminescence materials. [ABSTRACT FROM AUTHOR]

The synthesis and component of red phosphor, Sr 4 Al 14 O 25 : Mn, were optimized for application in white light-emitting diodes. The microstructure and morphology were investigated by the X-ray diffraction and scanning electron microscopy. Different valences of Mn ions in Sr 4 Al 14 O 25 were discriminated using the electron paramagnetic resonance and X-ray absorption near-edge structure spectroscopy techniques. The bond-valence theory was used to analyze the effective valences of Sr 2+ and Al 3+ in Sr 4 Al 14 O 25 . As a result, the strong covalence of Al 3+ in the AlO 4 tetrahedron other than in the AlO 6 octahedron is disclosed. The deep red emission is attributed to Mn 4+ occupying the center of AlO 6 octahedron. The mechanism of energy transfer is mainly through dipole–dipole interaction, revealed by the analyses of critical distance and concentration quench. A high color rendering white LED prototype with color-rendering index up to Ra 93.23 packaged by using the red phosphor demonstrates its applicability. [ABSTRACT FROM AUTHOR]

The predictable luminescent material design is always the holy grail for the scientists, especially for transition metal (TM) ions doped phosphors due to their high sensitivity to the crystal environments. In this perspective, driven by the photo spectroscopies data of TM ions from Sc to Zn (from atomic number 21 to 30) in diverse compounds from literature published in the past 70 years, we tentatively give a strategy from the electronic structure view with a specific focus on the tetrahedral symmetry field for TM ions in inorganic phosphors. We find the ground state position of a TM ion is predictable in the bandgap with an accuracy about ±0.23 eV. The strategy is a delightfully simple yet extremely powerful tool for tailoring the luminescent properties of TM doped phosphors combining the Tanabe-Sugano diagrams while without complicated theoretical calculations. The physics behind the relationships was deliberated with molecular orbital theory. The predictability of the ground state of 3dn transition metal ion will largely decode the underlying principles for the design of multi-functional TM doped materials in the future. • In tetrahedral sites, the ground state of TM ion induced defect levels could be well predicted with a deviation of ±0.23 eV. • The position of ground state of TM ions is not constant and increases nearly linearly with the top of the host valence bands. • Our prediction approach can immediately give the information about their excited state through the Tanabe-Sagano diagram. • Our work can facilitate the readers to smartly design the most possible 3d ion activated phosphors with their purpose. • This strategy is general, representing a significant step toward systematic prediction of a variety of functional materials. [ABSTRACT FROM AUTHOR]

Abstract: In this letter, Mn2+-doped CdS quantum dots were successfully synthesized with stearic acid as the stabilizer by a nucleation-doping method. Generally, Mn2+-doped emission was at ~585nm, which was well-established due to 6A1–4T1 transition of Mn2+ ions. Interestingly, a high-luminescence Mn2+-doped emission at ~563nm was observed in the Mn2+-doped CdS nanocrystals. This large blue shift explained that Mn2+ ions were deeply doped in nanoparticle cores in our doping method, leading to less splitting of Mn2+ energy level. The results of transmission electron microscopy and X-ray diffraction also demonstrated the small particle size (~4.2nm), monodispersity and high crystallinity. The quantum yield of the as-prepared nanocrystals was calculated ~41%. [Copyright &y& Elsevier]

Abstract: The phosphors of Sb3+ and Eu3+ activated YBO3 were synthesized via solid-state reaction. The crystal structure was investigated using X-ray diffraction analysis. The luminescence and energy transfer were investigated on the synchrotron radiation instrument, by exciting with different wavelengths at room temperature or as low temperature as 14K. The electron–lattice interaction between the activator Sb3+ and the host of YBO3 combined with the spin–orbit interaction of Sb3+ result in a large Stokes shift in Sb3+ emission, giving rise to no matchable energy levels for the energy transfer from Sb3+ to Eu3+. Nevertheless, the excitation energy could transfer from Bi3+ to Eu3+, which has the same ns2 electronic configuration as Sb3+. Taking advantage of the simultaneous isolated luminescence of Sb3+ and Eu3+, finally, the white luminescence from a single phosphor was tuned up by tailoring Sb3+ and Eu3+ concentrations in the YBO3 host, which shows potential application in deep ultraviolet light-emitting diodes (LEDs). [Copyright &y& Elsevier]

Abstract: The Gd3+ could play an intermediate role in energy transfer to produce light, while the Sb3+ promisingly served as a sensitizer or an activator in luminescence since its ns2–nsnp transition having a large cross section to capture excitation energy. In this work, the energy transfer between Gd3+ and Sb3+ in YBO3 host was studied. The phosphors were synthesized with a solid-state reaction method, and their crystal structure was examined with the X-ray diffraction analysis. The dependence of energy transfer on the distance between Gd3+ was revealed by changing Gd3+ and Sb3+ concentrations, respectively. The results revealed that excitation energy was transferred from Gd3+ towards Sb3+, which was contrary to the Bi3+→Gd3+ energy transfer that was previously reported in YBO3, although both Sb3+ and Bi3+ have the same ns2 electronic configuration. Moreover, the excitation energy would transfer among different Gd3+ ions via sublattice until trapped by Sb3+. [Copyright &y& Elsevier]

Abstract: To enhance the luminescence of (Sr,Ba)3SiO5:Eu2+ for white light-emitting diodes, a new method for the synthesis of phosphor was developed. In the proposed method, the mixture of large and nano SiO2 particles as a silica source was employed to control the nucleation and crystal growth of the material. The impurity phase (Sr,Ba)2SiO4, which easily coexisted with (Sr,Ba)3SiO5 was suppressed. Accordingly, the luminescence was enhanced significantly by the partial substitution of conventional SiO2 with nano SiO2. The improvement in crystallinity and morphology was examined with XRD and SEM. Moreover, the sintering temperature and the concentration of nano SiO2 was optimized. The results show that appropriate amount of nano SiO2 has pronounced effects on the nucleus formation and crystal growth, while excessive crystal seeds formed may hinder the growth of particles. A mechanism for this improvement was proposed. [Copyright &y& Elsevier]

Abstract: The phosphor of YBO3: Sb3+ was synthesized by solid state reaction. Its crystal structure was examined by using X-ray diffraction analysis. The morphology and particle size were characterized with a scanning electron microscopy. The properties of YBO3: Sb3+ luminescence was systematically studied by exciting borate host, the 1P1 and 3P1 levels of Sb3+ at the Ci and C 1 sites with 168, 203, 218, 252 and 262nm, respectively, measured on the synchrotron radiation instruments. The different configurations of emission spectra excited with variant wavelengths show the character of wavelength-selective excitation, which was attributed to different occupations of the Sb3+ site in the YBO3 crystal lattice. Moreover, strong electron–lattice interaction (i.e., the Jahn–Teller effect) between Sb3+ and YBO3 host was discriminated by comparing low temperature and room temperature spectra. The site-selective luminescence was confirmed by YBO3 activated with multiple Sb3+ concentrations. The spectral assignment was verified with fluorescence lifetime achieved by using the Time-Correlated Single-Photon Counting method. [Copyright &y& Elsevier]