| White-light emitting diode (W-LED) has been obtained through a blue LED (GaN chip) precoated with a yellow phosphor (Y1-aGda)3(Al1-bGab)512:Ce3+(YAG:Ce) and has been widely used in various applications such as full-color displays, liquid crystal display back lighting and traffic signals. However, this kind of white light has a low color rendering index(Ra<80) because the yellow light emission from the phosphor YAG:Ce lacks sufficient red emission. To overcome problems like this for W-LED, single-phased white-light phosphors have been an active research area in the study of luminescent materials. Although single-composition white-light phosphors for near-UV or UV excitation have been reported in the literature, satisfactory solution are much harder and novel phosphor is still desirable.Recently, with the development of near-UV/UV light chip, much attention has been paid to white-light emitting phosphor under ultraviolet light excitation.Ce3+, Tb3+and Eu3+ions are three important trivalent rare earth ions which has been used to produce blue, green and red emission. Ce3+functions as a high-efficiency emission center because4f-5d transitions in Ce3+allow parity. In addition, Ce3+is an efficient sensitizer to Tb3+. The energy-transfer (ET) processes between Ce3+and Tb3+in different hosts, such as alkaline earth sulfate, silicate, phosphate, fluoride, and so on, have been extensively investigated. However, luminescence dynamics and the ET processes between Ce3+and Tb3+in Sr2MgSi2O7have not been investigated. And the energy-transfer (ET) processes between Ce3+and Eu3+has not been investigated.In the present work, we report the first realization of such an idea. We demonstrate that it is possible to obtain white-emitting single-phase phosphor via chemical approaches with appropriate tuning of activator contents of Eu3+, Tb3+and Ce3+in Pyrosilicate (Sr2MgSi2O7) host lattices. The luminescent mechanism for the co-doped Eu3+, Tb3+and Ce3+cations in Sr2MgSi2O7has also been discussed.1. Synthesis and luminescent properties of the phosphors Sr2MgSi2O7 single-doped with Ce3+, Tb3+and Eu3+The phosphors Sr2MgSi2O7single-doped with Ce3+, Tb3+and Eu3+were synthesized by high temperature solid state reaction. The XRD patterns for these phosphors are measured. The results show that all these compounds are single-phase Sr2MgSi2O7.The emission spectrum of Sr2MgSi2O7:Ce3+, recorded at λ ex=327nm, shows a broad band with a maximum at387nm. The emission spectrum of Sr2MgSi2O7:Tb3+, recorded at λ ex=235nm, shows a green emission with a maximum at542nm. The emission spectrum of Sr2MgSi2O7:Eu3+, recorded at X ex=327nm, shows a red emission with a maximum at610nm. The PL intensities of the phosphors single-doped with Ce3+or Tb3+grow as the concentrations grow except Ce3+.In a word, under327nm excitation, the PL intensities of Sr2MgSi2O7:0.0065Ce3+, Sr2MgSi2O7:0.07Tb3+and Sr2MgSi2O7:0.07Eu3+phosphors show a maximum. The phosphors Sr2MgSi2O7single-doped with Ce3+, Tb3+and Eu3+can be excited by UV chip, and the phosphors are three kinds of single-phase phosphors for WLED-based UV-chip.2. Synthesis and luminescent properties of the phosphors double-doped with Ce3+, Tb3+and Eu3+The emission spectrum color of phosphors Sr2MgSi2O7double-doped with Ce3+, Tb3+and Eu3+could be controlled by were synthesized by adjusting the concentrations of Ce3+and Tb3+. It had been found that the nominal composition Sr2MgSi2O7:0.02Ce3+,0.05Tb3+phosphor provides a white emission (0.279,0.310) that is very close to the standard white (x=0.33, y=0.33).high temperature solid state reaction. Sr2MgSi2O7double-doped with Ce3+, Eu3+can be excited by UV chip. Ce3+shows a blue-purple emission. The peak at610nm belongs to the red emission of Eu3+. It had been found that the nominal composition Sr2MgSi2O7:0.05Ce3+,0.03Eu3+phosphor provides a white emission (0.312,0.303) that is very close to the standard white (x=0.33,y=0.33), which shows that it is a potential single-phased white phosphor for LED-based UV-chip. And we investigated the properties of phosphors Sr2MgSi2O7double-doped with Tb3+and Eu3+. The emission of Eu3+,Tb3+å'ŒEu2+could be observed. We discussed the ET processes and electron transfer phenomenon between Eu3+, Eu2+and Tb3+in Sr2MgSi2O7. The further research is a meaningful exploration3. White-light emitting and energy transfer mechanism in the phosphor Sr2MgSi2O7co-doped with Ce3+, Tb3+and Eu3+The phosphor designed as Sr2MgSi2O7:Ce3+, Tb3+, Eu3+were prepared by the high temperature solid state reaction by orthogonal test. Crystallization and optical properties were investigated by using power X-ray.The energy transfer processes from Ce3+to Tb3+and from Ce3+to Eu3+were discussed.It had been found that the nominal composition Sr2MgSi2O7:0.010Ce3+,0.05Tb3+,0.03Eu3+phosphor provides a white emission (0.337,0.313) that is very close to the standard white (x=0.33, y=0.33), which shows that it is a potential single-phased white phosphor for LED-based UV-chip. |
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