| Since the first white light-emitting diode (LED) based on the InGaN chip was developed, white LED technique has gradually developed into an important kind of solid-state illumination, In comparison with conventional incandescent and fluorescent lamps, the white LEDs show many projecting advantages such as energy saving, environment friendly, small volume, short response time, long life time and so on. The most commonly method is to combine a phosphor with a GaN LED chip, and this is called as phosphor-conversion method. As an essential part, phoshphors strongly affect the quality of LEDs, such as luminous efficiency, color temperature, color rendering index, life time and so on. So the phosphor is very important in white light LED. Traditional phosphors usually based on the sulfide, aluminate and silicate. In recent years, the rare-earth doped (oxy)nitride phosphors have attracted much attention. In (oxy)nitride phosphors, the nephelauxetic effect and the relative low electronegativity value of N3-ion cause the large splitting of5d energy levels, which makes the redshift of the excitation and emission band, so it makes them as a potential candidate for the UV-LED and blue LED. The (oxy)nitride phosphors also have the advantages of better flexibility, composition-tunability and higher thermal and chemical stability. But the preparation of (oxy)nitride phosphors is very difficult and the luminescence mechanism have not been studied deeply.So this thesis focuses on the preparation of several oxynitride phosphors and the luminescence mechanism. The main works were contained as below:(l)Yellow-orange oxynitride Ca-a-SiAlON:Eu2+phosphors with the compositions of Cao.8Si9.2Al2.8O1.2N14.8:xEu2+(x=0-0.24) were obtained via carbothermal reduction and nitridation method. The XRD analysis indicated the high purity and crystalline of sample, and no residual carbon existed. The resulting phosphors can absorb light in the range of300～500nm efficiently and show a single intense broad emission band in the wavelength range of500-700nm. It reveals that Ca-a-SiAlON:Eu2+is a good candidate for warm white-LEDs (color temperatures,3270-2260K). (2)Cai.8Si8.2Al3.7N16:Eu2+phosphor was abtained by changing the oxygen content of general formula Mxv+Si12-(m+n)Alm+OnnN16-n. The samples could efficiently excited by near ultraviolet or blue LED chip, and show a single intense broad emission band at580～601nm. By contrast, the luminescence properties of Ca1.8Si8.2Al3.7Ni6:Eu2+are better than Ca-a-SiA1ON:Eu2+.(3)Rare-earth-doped P-SiAlON phosphors, with the compositions of Si6-zAlzOzN8-z:Re (z=1, Re=Ce3+, Tb3+, Sm2+and Dy3+), were prepared by a solid-state reaction at1600℃under atmospheric pressure. The energy transfer from Ce3+to Tb3+ions in Si5A1ON7:Ce3+,Tb3+has been studied. The emission spectra consist of broad band and line peaks at room temperature, which are ascribed to the4f55d1â†'4f6and5Doâ†'7FJ transitions of Sm2+respectively. Dy3+doped β-SiA1ON emits approximate white light. In addition, the up-conversion luminescence properties have been studied firstly in β-SiAlON:Ln3+(Ln=Yb/Ho, Yb/Er)(4)Y4Si2O7N2:Ce3+was synthesized using a solid-state reaction and its crystal structure was introduced in detail. Ce3+-doped Y4Si2O7N2exhibited a broad emission band and the maximum emission wavelength could be tuned from blue (λem=450nm) to green (λem=515nm) by increasing the concentration of Ce3+. The red-shifting behavior is mainly attributed to two factors:crystal field strengthening and radiation re-absorption of the high energy emission. |
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