Synthesis And Properties Of Light-converting Materials For Light-emitting Diodes (LEDs)

Semiconductor solid lighting technology is the forefront of green lighting and materials research in the world. One route to realize white light outputting is based on the combination of suitable fluorescent conversion materials and a near ultraviolet or a blue light-emitting diode (LED). Therefore, zinc oxide and Eu²⁺-activated strontium aluminate green phosphors were synthesized for the fluorescence conversion of near ultraviolet light-emitting diode(NULED), and their properties were examined by means of photoluminescent (PL) spectra, thermoluminescent (TL) spectrum, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Some additives were used to enhance the luminous efficiency and stability of phosphors, and the relating mechanisms were discussed.[1] Zinc oxide green phosphors with hexagonal wurtzite structure have been synthesized by calcining zinc sulfide with some certain amount of halides MX (X=F, Cl, Br, I; M=Na, K, NH₄, Zn, ZrO). It is proved that the halides possess dual functions both as flux and dopant for promoting light-emitting performance of ZnO, which provided a new route to synthesize highly efficient green phosphors at lower calcining temperature (700-800℃).[2] The contents of sulfur (S) and halogen elements (such as Cl) in the phosphors were found to be 0.6-2% and 3-4% respectively. So the synthesized ZnO could be considered as a new kind of zinc oxide phosphors co-doped with sulfur and chloride. The ultraviolet-visible absorption spectra showed that the doping of sulfur and chloride can reduce the absorption intensity originated from the transition from valence band(VB) to conductor band(CB) of ZnO, at the same time, a new absorption peak was found at around 3.06eV (399nm). The emission spectra of ZnO phosphors displayed a wide peak at around 506-510nm, and no exciton emissiom was observed at 380nm. The excitation spectra were composed of two peaks, corresponding to the transition from VB to CB (below 370nm) and from VB to defect center in band gap...