A series of Ba 3 Lu 4 O 9 :Er 3+ /Yb 3+ (EYBLO) phosphors co-doped with F À ions were synthesized by a simple solid-state reaction method. The results showed that the primary rhombohedral structure was maintained and the crystal lattice began to shrink when F À ions were introduced into the host matrix to occupy the O 2À site. The agglomerations and the impurities (OH À and CO 2 ) with higher phonon energy on the sample surface could be minimized and the sample crystallinity could be improved. Under 980 nm laser diode excitation, the green and red UC emissions of the EYBLO:0.4F À sample show nearly 5-and 7.5-fold enhancements in contrast to F À -free EYBLO. The upconversion luminescence can be finely tuned from yellow to red light to some extent by increasing F À concentration. Based on pumppower dependence and decay lifetime analysis, the energy level diagram was illustrated and the upconversion energy-transfer mechanism was discussed. The green and red emission enhancements are attributed to the modification of the local crystal field of Er 3+ ions and reduction of crystal site symmetry.The cross-relaxation and back-energy-transfer processes play an important role to enhance the red/ green UC emission intensity ratios. The fluorescence intensity ratio technique was employed to investigate the temperature sensing behavior of the synthesized phosphors. The temperature sensing properties can be enhanced by doping of F À ions, and the maximum sensitivity is found to be 44.57 Â 10 À4 K À1 at 523 K. It is promising to provide an alternative approach for enhancing UC luminescence and the temperature sensitivity in oxide matrixes and then obtain high-quality optical temperature-sensing materials by simply co-doping F À ions.
Disc-modified nanohelices (DNHs) of ZnO were synthesized by thermal evaporation. The
ZnO DNHs are constructed by nanowires which are regularly attached with discs. The axis
of the DNH structure is along the ZnO[0001] direction. The pitch distance, the mean
diameter, and the thickness of the nanowires are uniform for each ZnO DNH. Within one
period there are 12 discs symmetrically attached on the surfaces of the nanowires.
The discs are composed of nanometre-sized ZnO crystal cores and amorphous
SiO2
shells. The mechanism of formation of the nanostructures is also discussed.
Mn 4+ activated fluoride phosphors have been considered as highly promising red component for warm white light-emitting diodes in recent years. In this paper, we successfully prepared the K 2 TiF 6 : Mn 4+ red phosphors in H 3 PO 4 /KHF 2 liquid instead of the hypertoxic HF liquid. The impact factors, such as the amount of F source, the reaction temperature, reaction time, and the luminescence mechanism are investigated in detail. We found that K 2 TiF 6 : Mn 4+ shows pure red emission and can be excited by blue lights, which can perfectly match the InGaN chip based white light-emitting diodes. Most importantly, K 2 TiF 6 : Mn 4+ exhibits excellent quenching behavior and shows small color shift in the temperature range of 300-475 K. Our researches could provide a green synthetic strategy to obtain the K 2 TiF 6 : Mn 4+ phosphors and contribute to the optimization of red phosphors for white light-emitting diodes.
Green emitting BaAl 1.4 Si 0.6 O 3.4 N 0.6 :Eu 2+ phosphors with a uniform sphere-like morphology were successfully prepared via molten salt synthesis (MSS) method using NaNO 3 as the reaction medium. The obtained phosphors exhibited a broad excitation spectrum ranging from 250 to 460 nm and a strong green emission peak at 510 nm due to the 4f 6 5d 1 -4f 7 ( 8 S 7/2 ) transition of Eu 2+ ions. Under excitation at 365 and 450 nm, the optimal emission intensities of the sample obtained by using molten salt are 17% and 13% higher than those of the sample prepared via conventional solid state (SSR) method, respectively. The quenching concentration of Eu 2+ ions is 5 mol%, and dipole-dipole interaction is responsible for the concentration quenching of Eu 2+ ions in this type of phosphor. The mechanism of thermal quenching is discussed by using the configuration coordinate model and thermal quenching temperature is ∼200 • C. Elemental mapping and energy dispersive X-ray spectroscopy (EDS) spectra proved the formation of the desired BaAl 1.4 Si 0.6 O 3.4 N 0.6 :Eu 2+ materials.
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