Xiaojuan Liang

Facile synthesis of a thermally stable Ce3+:Y3Al5O12 phosphor-in-glass for white LEDs

This study outlines a general but convenient approach towards the synthesis of a Ce3+:Y3Al5O12 phosphor-in-glass (PiG) with a relatively low sintering temperature. A comparative study of the as-synthesized PiG and glass ceramic prepared using a conventional route was carried out to explore the structural, morphological and optical properties. In addition, the effect of phosphor concentration and the sintering temperature/time on the luminescence properties was systematically investigated. Notably, we fabricated a high-performance white LED based on PiG with a high luminous efficacy (125 lm W−1), low correlated colour temperature (4329 K) and colour rendering index of 68. Furthermore, the PiG material demonstrates an excellent thermal stability up to 150 °C, superior to the low thermal stability of conventional Ce3+:Y3Al5O12 doped silicone. Therefore, we present a transparent phosphor glass with desirable potential for application in high powered W-LEDs.

Direct synthesis of highly luminescent Cu–Zn–In–S quaternary nanocrystals with tunable photoluminescence spectra and decay times

We report the direct synthesis of highly luminescent Cu–Zn–In–S (CZIS) quaternary nanocrystals (NCs) in the non-coordinating solvent 1-octadecene (ODE) using chloride salts of Cu, In, and Zn as metal precursors in the presence of oleic acid and dodecanethiol. The resulting CZIS NCs had a narrow size distribution with an average diameter of 2.5 nm. The photoluminescence spectra can be tuned from 400 nm–850 nm by varying the Cu : Zn precursor ratio, and a relatively high photoluminescence quantum yield (PL QY) of 46% was obtained without any post-processing. The PL decay times of the as-prepared CZIS NCs were tunable via controlling the Cu : Zn precursor ratio and reaction time. The photoluminescence mechanism of the CZIS nanocrystals was discussed using the PL decay curves. EDS analysis revealed that the resulting CZIS NCs were Cu-deficient, and the internal defect-related emission process could be strongly promoted by the large Cu deficiency which is associated with the improvement of PL QY.

Carbon dot-doped sodium borosilicate gel glasses with emission tunability and their application in white light emitting diodes

Carbon dot (CD)-doped sodium borosilicate gel (CD-NBS gel) glasses were successfully prepared by incorporating the CDs into sodium borosilicate networks. The structural and luminescence properties of highly flexible CD-NBS gel glasses with 5% wt% to 70 wt% CDs were studied. Images of the CD-NBS gel glasses captured using a transmission electron microscope demonstrated the uniformity and good dispersibility of the glasses. Red-shifted emission and enhanced quantum efficiency were observed when the doping concentration of CDs in the NBS gel glasses increased. The enhanced fluorescence properties of the CD-NBS gel glasses were considered to originate from the surface modification of CDs with high dopant concentration in the gel glasses. CD-based white light-emitting diodes (W-LEDs) were developed by combining the yellow light-emitting CD-NBS gel glasses with blue GaN-based LED chips. The as-fabricated W-LEDs exhibited the optimised colour coordinates of (0.32, 0.33), the colour rendering index up to 78.9, and the maximum luminous efficacy exceeding 58.1 lm W−1 by the use of the CD-NBS gel glasses at different concentrations of CDs. These results indicate that this new kind of CD-NBS gel glass would be a promising candidate for W-LEDs.

Valence State Control and Third-Order Nonlinear Optical Properties of Copper Embedded in Sodium Borosilicate Glass

The integrated and transparent sodium borosilicate glasses that contain copper exhibiting different colors, that is, red, green, and blue were synthesized by combining the sol-gel process and heat treatment in H2 gas. To reveal substantially the cause of different colors in the glass, X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) were systematically applied to investigate and determine the microstructure of the doped matter. The results showed three different crystals had formed in the red, green and blue glass, and the sizes of these crystals were range from 9 to 34, 1 to 6, and 1 to 5 nm, respectively. The valence state of copper was further analyzed by X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). The third-order nonlinear optical properties of the glasses were investigated by using Z-scan technique at the wavelength of 800 nm. Interestingly, the third-order nonlinear absorption of the red, green, and blue glass can be successfully controlled from reverse saturable absorption, no absorption to saturable absorption and the optical nonlinear susceptibility χ((3)) of the red, green and blue glass were estimated to be 6.4 × 10(-14), 1.6 × 10(-14), and 2.6 × 10(-14) esu in the single-pulse energy of 0.36 μJ, respectively.

Synthesis and luminescence properties of a H2 annealed Mn-doped Y3Al5O12:Ce3+ single crystal for WLEDs

A Czochralski grown Mn-doped Y3Al5O12:Ce3+ single crystal was thermally annealed in H2 atmosphere at different temperatures for 6 h and the corresponding absorption spectra, emission spectra, quantum yield (QY) and color-electric performance of Ce,Mn:YAG single crystal wafers were investigated before and after annealing. Moreover, the electron paramagnetic resonance (EPR) of doped Mn ions and a possible energy transfer process from Ce3+ to Mn2+ ions were discussed in detail. The corresponding results demonstrated that the H2 annealing process partly generated the intensity of luminescence spectra and improved the values of quantum yield and luminous efficacy (LE). H2 annealing at 1550 °C is the most optimal annealing conditions. After annealing, a maximum luminous efficacy reaching 119.93 lm W−1 and a color rendering index of 73.6 at a correlated color temperature of 5674 K were obtained, which demonstrates that the Ce,Mn:YAG single crystal is expected to be an optimal candidate for white LEDs.

Biomolecule-assisted Solvothermal Synthesis of Bismuth Sulfide Nanorods

A simple biomolecule-assisted synthetic route has been successfully developed to prepare bismuth sulfide (Bi2S3) nanorods under solvothermal conditions. In the synthetic system, pentahydrate bismuth nitrate was employed to supply Bi source and L-cystine was used as sulfide source and complexing agent. The morphology, structure, and phase composition of the as-prepared Bi2S3 products were characterized by X-ray diffraction (XRD), energy dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM). The experimental results show that the nanorods have uniform diameter of 100-200 nm and length of 2-4 μm. The possible formation mechanism for the bismuth sulfide nanorods was discussed.

A novel green-yellow emitting phosphor Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ and its luminescence properties

Abstract We described the synthesis and luminescence of Ca 1.5 Y 1.5 Al 3.5 Si 1.5 O 12 :Ce 3+ phosphor for light emitting diode (LED). The crystallinity, morphology, structure, and luminescence spectra were examined by X-ray diffraction, field emission-scanning electron microscopy and photoluminescence spectroscopy. The results showed that Ca 1.5 Y 1.5 Al 3.5 Si 1.5 O 12 :Ce 3+ phase was a dominating phase with little impurity phase peaks of Y 2 O 3 when the sintered temperature reached to 1400°C. Field emission scanning electron microscopy (FE-SEM) images showed the particle size of the phosphor was about 3 μm. Meanwhile, the excitation and emission spectra indicated that the as-prepared phosphors could be effectively excited by blue (460 nm) light and the excitation spectrum showed a broad band extending from 400–500 nm, while emission spectrum showed a broad yellow band peaking at 534 nm. The decay curve at the emission peak consisted of fast and slow components. The Ca 1.5 Y 1.5 Al 3.5 Si 1.5 O 12 :Ce 3+ should be a promising yellow phosphor for near blue-based white-light-emitting diodes (LEDs).

CsPbBr3:xEu3+ perovskite QD borosilicate glass: a new member of the luminescent material family

Eu3+ ions were introduced into the lattices of CsPbBr3 perovskite QDs and a tunable multicolour emission from CsPbBr3:xEu3+ perovskite QD glass was successfully obtained. Multicolour LEDs that were fabricated by combining the as-prepared CsPbBr3:xEu3+ QD glasses with a UV chip were also researched in this study.

Upconversion luminescence of cerium-stabilized high temperature phase zirconia phosphors with a high Er3+ doping concentration

Oxide upconversion (UC) materials usually have lower luminescence efficiency (LE) due to their low quenching concentration and high phonon energy. To solve this issue, we have investigated in detail cerium-stabilized high temperature phase zirconia based phosphors (Zr(0.85−x)Ce0.15O(2−0.5x):xEr3+) with different doping concentrations of Er3+ and have achieved a red phosphor with an Er3+ concentration as high as 10 mol%, which will have broad prospects for its application as a new UC material. The results demonstrate that adjusting the host structure of the UC material can increase its quenching concentration and thereby the LE will be improved. The introduction of Ce4+ into ZrO2 not only stabilizes its phase but also improves the LE of the ZrO2 based UC material. The Er3+ coordination state changes with an increase of Er3+ concentration in the UC phosphors based on cerium-stabilized zirconia. The corresponding luminescence process translates into the cross relaxation from the excited state absorption, UC luminescence changes from green to red and the red emission intensity becomes stronger and stronger and achieves its maximum when the Er3+ concentration is 10 mol%.

Facile synthesis and optical properties of Ce:YAG polycrystalline ceramics with different SiO2 content

Ce:YAG polycrystalline ceramics with different SiO2 content were successfully prepared by a single-step melt-quenching method. The characterization of the resulting polycrystalline ceramics was accomplished by using X-ray powder diffraction, field emission scanning electronic microscopy and energy dispersive X-ray spectroscopy. Then, the optical properties were investigated using a fluorescence spectrometer. It is found that the glass matrix becomes a glassy state more easily, the photoluminescence excitation (PLE) and PL intensity decrease obviously and crystallization of YAG is difficult to generate as the SiO2 content increases. Whats more, the intensity of the blue LED decreases and that of the yellow emission band instead increases and saturates at a SiO2 content of 32 mol% in the electroluminescent (EL) spectra. Afterwards, the photoelectric performance was studied by an LED spectrometer. As a consequence, the constructed polycrystalline ceramic based WLED exhibits a high luminous efficiency of 74.44 lm W−1, and a correlated color temperature of 5351 K as well as a color rendering index of 75.91, which reveals the prominent feasibility of the present polycrystalline ceramic material in WLED applications.