Quansheng Wu

A Single-Component White-Emitting CaSr2Al2O6:Ce3+, Li+, Mn2+ Phosphor via Energy Transfer

A series of single-component Ce(3+), Li(+), Mn(2+) ions codoped color-tunable CaSr2Al2O6 phosphors were synthesized by a high-temperature solid-state reaction, and the photoluminescence properties as well as the energy transfer mechanism from Ce(3+) to Mn(2+) ions have been investigated in detail. The Ce(3+) activated phosphors have strong absorption in the range of 250-420 nm and can give a blue emission centered at about 460 nm. When Mn(2+) ions are codoped, the emission of CaSr2Al2O6:Ce(3+), Li(+), Mn(2+) phosphors can be tuned from blue to red through adjusting the doping concentration of the Mn(2+) ions, under the irradiation of 358 nm. When the concentration of Mn(2+) is increased to 0.02, a warm-white light can be obtained with good CIE coordinates of (0.388, 0.323) and a low CCT of 3284 K. The energy transfer mechanism from the Ce(3+) to Mn(2+) ions is demonstrated to be a quadrupole-quadrupole interaction based on the analysis of the decay curves of the phosphors. The thermal quenching stability was also investigated. The results indicate that CaSr2Al2O6:Ce(3+), Li(+), Mn(2+) samples might have potential applications in w-LEDs.

Preparation of Sr1−xCaxYSi4N7:Eu2+ solid solutions and their luminescence properties

A series of quaternary nitride solid solutions with a general formula of Sr1−xCaxYSi4N7:Eu2+ (1 atom%) were synthesized by the carbothermal reduction and nitridation (CRN) method. The XRD patterns confirm the formation of a solid solution of Sr1−xCaxYSi4N7:Eu2+ (0 ≤ x ≤ 0.5). With an increase in x, the emission spectra shift from 540 nm to 564 nm under n-UV excitation. In addition, the temperature dependence of the PL intensity was investigated. The thermal stability is comparable to that of the commercial (Ba,Sr)2SiO4:Eu2+ phosphor. All the results indicate that the solid solution Sr1−xCaxYSi4N7:Eu2+ can be a good candidate of phosphor applicable to n-UV LEDs for solid-state lighting.

Synthesis, crystal structure and luminescence properties of a Y4Si2O7N2:Ce3+ phosphor for near-UV white LEDs

A near-UV excited phosphor, Y4Si2O7N2:Ce3+, was synthesized using a solid-state reaction. The crystal structure and luminescence properties were studied. Y4Si2O7N2 crystallizes in a monoclinic unit cell with space group P21/c, lattice constants a = 7.5678(2) A, b = 10.4529(1) A, c = 10.7779(3) A and β = 110.06°, and cell volume = 800.85(2) A3. The crystal structure of Y4Si2O7N2, featuring Si(O,N)4 polyhedra, is provided, and there are four different Y3+ coordination environments with two different coordination numbers in the structure. Ce3+-doped Y4Si2O7N2 exhibited a broad emission band, and the maximum emission wavelength could be tuned from blue (λem = 450 nm) to green (λem = 515 nm) by increasing the concentration of Ce3+. The quantum efficiency was determined to be about 47%. The results show that Y4Si2O7N2:Ce3+ is a candidate for use as a conversion phosphor for near-UV white LED applications.

Synthesis and luminescence characteristics of nitride Ca1.4Al2.8Si9.2N16:Ce3+, Li+ for light-emitting devices and field emission displays

A green-emitting nitride phosphor Ca1.4Al2.8Si9.2N16:Ce3+, Li+ (CASN:Ce) has been successfully synthesized which is applicable to near-ultraviolet based light-emitting diodes (LEDs) and field emission displays (FEDs). The characteristic photoluminescence (PL) properties were studied in detail by PL excitation, emission spectra and time-resolved spectroscopy. CASN:0.10Ce exhibits broad-band green emission centered at ∼525 nm (FWHM ≈ 135 nm) under 395 nm excitation and with excellent thermal stability. The effect of host lattice composition on PL properties was also discussed. The cathodoluminescence (CL) spectra as a function of accelerating voltage and probe current were also studied. Excellent degradation resistance properties with good color stability were obtained by continuous low-voltage electron-beam excitation of the phosphor.

Antioxidant phenolic glucosides from Gentiana piasezkii

An extract of Gentiana piasezkii afforded a new arbutin derivative 6′-O-vanilloylarbutin (1) and a new flavone-C-glucoside 7-O-feruloylorientin (2), together with four known flavonoids lutonarin (3), saponarin (4), isoorient (5) and luteolin (6). Their structures were established based on spectroscopic methods including 2D NMR (COSY and gHMBC) techniques. Compounds 1, 2, 5 and 6 were evaluated for the antioxidant activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay system.

Structure, photoluminescence and abnormal thermal quenching behavior of Eu2+-doped Na3Sc2(PO4)3: A novel blue-emitting phosphor for n-UV LEDs

A novel blue-emitting phosphor Na3Sc2(PO4)3:Eu2+ was successfully synthesized by solid-state reaction. The crystal structure, bandgap, and photoluminescence properties were investigated in detail. Under n-UV excitation, the NSP:Eu2+ phosphor exhibits a narrow blue emission peaking at 458 nm with a FWHM of about 50 nm. The concentration quenching mechanism of the NSP:Eu2+ is dominated by the dipole–dipole interaction. Moreover, the NSP:Eu2+ shows better PL intensity, colour purity and thermal quenching properties compared to the commercial BAM phosphor. Non-equivalence replacement of Eu2+ ions for Na+ ions causing defects, inducing the abnormal thermal quenching behaviour. All these results suggest that the NSP:Eu2+ phosphor can be a potential candidate for n-UV LED applications.

Novel optical characteristics of Eu2+ doped and Eu2+, Ce3+ co-doped LiSi2N3 phosphors by gas-pressed sintering

Eu2+ doped and Eu2+, Ce3+ co-doped LiSi2N3 phosphors were successfully prepared by gas-pressed sintering in this study. The dominant excitation band of LiSi2N3:Eu2+ was found at about 355 nm and exhibited a broad-band yellow emission centered at 592 nm instead of the early reports of 310 nm and 580 nm, respectively. The shifting behavior dominantly contributed to different oxygen content in the host. The second luminescent center formed by the introduction of oxygen into nitride phosphors was discussed in detail. The detailed energy transfer mechanism from Ce3+ to Eu2+ in the LiSi2N3 host is also reported and a notable unusual redshift behavior was observed in Eu2+, Ce3+ co-doped LiSi2N3 phosphors.

The pure-phase Ba3−xCaxSi6O12N2:Eu2+ green phosphor: synthesis, photoluminescence and thermal properties

The promising green oxynitride phosphor, Ba3−xCaxSi6O12N2:Eu2+, was synthesized at 1350 °C for 5 hours under a reducing N2/H2 (5%) atmosphere via the solid-state reaction method. The XRD patterns confirm the formation of the pure phase of Ba3−xCaxSi6O12N2:Eu2+. With an increase in x, the emission spectra shift from 525 nm to 536 nm under near-UV (n-UV) excitation. Accordingly, we propose the underlying mechanisms for the red-shift of the emission spectra by adjusting the cation composition in the host. The influence of the size mismatch on the thermal quenching is also observed. The as-prepared green phosphor exhibits great thermal quenching property, with the remaining 83% of the initial emission intensity measured at 150 °C. The quantum efficiency is measured to be 35.2%. All the results indicate that the Ba3−xCaxSi6O12N2:Eu2+ can be a good candidate phosphor applicable to n-UV light-emitting diodes for solid-state lighting.

Synthesis, structure and photoluminescence properties of Ca2LuHf2(AlO4)3:Ce3+, a novel garnet-based cyan light-emitting phosphor

A novel garnet phosphor, Ca2LuHf2(AlO4)3:Ce3+ (CLHA:Ce3+), was successfully designed and synthesized using a solid-state method. Its crystal structure, band structure and photoluminescence properties were investigated in detail. Under n-UV excitation, CLHA:Ce3+ exhibited cyan to blue-green emission depending on the Ce3+ concentration. The QE of the optimal sample was 50.3%. The concentration quenching mechanism of the Ce3+ emission was dominated by dipole–dipole interactions. A novel method to obtain white light was developed by combining the CLHA:Ce3+ phosphor with a CaAlSiN3:Eu2+ red phosphor. Both the emission intensity and thermal stability of CLHA:Ce3+ were found to be superior to those of the commercial (Sr,Ba)2SiO4:Eu2+ phosphor. All of the results indicate the CLHA:Ce3+ phosphor to be a promising candidate for application in white LEDs.

Novel red and green emitting Li2SiN2:Eu3+/Tb3+ phosphors with a broad charge transfer band

In this work, a broad excitation band of Li2SiN2:Eu3+ with the peak at 357 nm has been found and investigated. The photoluminescence, morphologies and thermal stability of the samples were also measured. Under excitation at 357 nm and 300 nm, sharp red and green light can be observed due to the 5D0–7F2 transition of the Eu3+ ions and the 5D4–7F5 transition of the Tb3+ ions, respectively. According to the Diffuse reflectance spectra in combination with the energy level diagram of Li2SiN2:0.02Eu3+, we deduced that the broad excitation bands belong to the charge transfer band (CTB), which have also been observed in Li2SiN2:Tb3+ with the peak at 271 nm. And the thermal stabilities of the samples have been found to be connected with the CTB.