| Single-phase white-emitting phosphor has been aroused extensive interest in the field of white light-emitting diodes(w-LEDs) due to the advantages such as color stability, good reducibility color, highly luminous efficiency and low cost, etc. This thesis fucuses on Li4SrCa(SiO4)2 based single-phase white phosphor by co-doping different kinds of rare earth ions.An efficient, thermal stable single-phase phosphor Li4SrCa(Si O4)2 doped with rare earth ions was synthesized by a traditional solid-state reaction. According to the luminescent properties of single-doped Ce3+ phosphor with different concentrations, two different Ce3+ concentrations were selected for the co-doping processes on the purpose of realizing single-phase white emitting under near UV light. The luminescent properties of ht phosphors were also characterized. The energy transfer from Eu2+ to Tb3+/Mn2+, Ce3+ to Tb3+/Mn2+ and Ce3+ to Eu2+ in Ce3+/Eu2+/Tb3+/Mn2+ codoped phosphors were studied in detail based on Ce3+ with low concentration. The energy transfer from Ce3+ to Tb3+/Mn2+ based on Ce3+ with higher doping concentration were also studied.In order to study the order of site substitution, a series of experiments by co-doping Ce3+ with La3+/Lu3+/Gd3+ were designed.Single-doped Ce3+ phosphors can emit both a near-UV light centered at 345 nm and a blue light peaking at 414 nm when Ce3+ occupies the Sr2+ and Ca2+ site, respectively. The internal quantum efficiency(IQE) of near-UV emitting LSCSO:0.03Ce3+ is as high as 97%,while the external quantum efficiency(EQE) is 66%.Based on the luminescent properties of single-doped Ce3+, two different doping concentrations were selected for the co-doping researches. For Ce3+ with low concentration(0.03), analyses indicate that energy transfer from near-UV emitting Ce3+ to Tb3+ and Mn2+ are more efficient than that from blue Ce3+/Eu2+. White emitting LSCSO:Ce3+,Eu2+,Tb3+,Mn2+ phosphor is realized by well adjusting the concentrations of activators, in which Ce3+ acts as a sensitizer while Eu2+, Tb3+ and Mn2+ are activators. Optimized white light sample is LSCSO: 0.03Ce3+, 0.01Eu2+, 0.06Tb3+, 0.04Mn2+. The IQE and EQE values of the white emitting phosphor are 56% and 43%, respectively. The CIE is(0.332, 0.278) and the CRI is 81.6. The emission intensity of the white phosphor at 150 °C remains 76% of that at room temperature(25 °C). The results indicate that the single-phase white emitting phosphor may have potential applications in w-LEDs.The luminescent properties of Ce3+ co-doped with no-emitting rare-earth ions, such as Lu3+, La3+ and Gd3+, were studied. Results show that co-doping with Gd3+ and Lu3+ will results in an increasing of the emission band at 345 nm, due to the increase of Ce3+ amount on Sr2+ site. While co-doping with La3+ will increase the emission intensity of the 414 nm band, which is due to the fact that La3+ prefers to occupy the Sr2+ site than Ca2+ site.When the concentration of 0.12Ce3+ is selected, only co-coped Ce3+,Tb3+,Mn2+ can achieved white light emission. The white light is realized by combining blue emitting Ce3+ on Ca2+ site with green emitting Tb3+ and red Mn2+. The CIE of optimized sample is(0.383,0.326). The energy transfer was studied by using the decay curves, PL and PLE spectra, combined with the results of the phosphors based on the low concentration of Ce3+.With the development of UV chip technology, these two white light phosphors show potential applications as phosphors in the field of w-LEDs. |
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