Investigation On The Energy Transfer And Luminescent Mechanism Of Rare Earth/Transition Matal Ions Doped Glasses For White Led

There has been a growing focus on white light-emitting diode (W-LED) in recent years due to their energy conservation, environment protection, long lifetime, high lighting efficiency, good thermal stability and so on. Currently, a potential method to obtain W-LED is combining ultraviolet LED (UV LED) with single-phase multi-activators. And compared to conventional phosphors used for W-LED, fluorescent glasses show excellent optical properties, better mechanical properties, lower production cost, simpler manufacturing procedures and an epoxy-resin-free assembly process. Thus it is interesting to develop single-phase fluorescent glassses capable of generating white light under UV chips excitation. Besides, most rare earth (RE) raw materials are very expensive. Moreover, some oxides, chlorides and citrates of RE elements are toxic and harmful. These shortcomings greatly limit the application of RE raw materials. Hence, searching for low-cost,"green" luminescent glasses, which do not contain RE ions, has been an interesting and important project in the development of new luminescent materials. In this thesis, transparent Ce3+/Tb3+, Ag/Eu3+,(Cu+)2Eu3+, Cu+/Sm3+and Sb3+/Mn2+doped silicate glasses were prepared by melt-quenching technique. The luminescent properties of luminescent centers, efficient energy transfer process between luminescent centers were systemically investigated through transmittance spectra, excitation spectra, emission spectra and decay curves:1. Ce3+/Tb3+doped soda-lime silicate glasses:Tuning the content of Tb3+can generate the varied hues from blue to white and eventually to yellowish green in Ce3+/Tb3+doped samples due to the efficient energy transfer process from Ce3+to Tb3+. And the maximum energy transfer efficiency can reach45.7%. 2. Ag/Eu3+doped oxyfluoride glasses:The enhancement of Eu3+emission coming from the effect of different types of Ag species:Ag nanoparticles, ML-Ag (very small molecule-like, non-plasmonic Ag particles) and isolated Ag+in a system were firstly investigated. Under resonant excitation (λex=464nm), enhancement of Eu3+emission by four times is attributed to the local-field surface plasmon resonance effect of Ag nanoparticles. Under nonresonant excitation, significant enhancements of Eu3+emission by540times (λex=350nm) and75times (λex=270nm) are ascribed to efficient energy transfer from ML-Ag and isolated Ag+to Eu3+, respectively. Moreover, white light emission is realized by combination with Eu3+(red), ML-Ag (green), and isolated Ag+(blue).3.(Cu+)2/Eu3+doped soda-lime silicate glasses:(Cu+)2single-doped samples present green-emitting light under UV light excitation. The excitation and emission bands of (Cu+)2show red shift with increasing (Cu+)2content, which may be explained as follows: with increasing Cu+content, the Cu+-Cu+distance is decreased and the overlap of s excited states is increased, then pushing s states closer to d ground state. Thus, shortening of Cu+-Cu+distance would produce red shift. For (Cu+)2/Eu3+doped samples, efficient energy transfer process from (Cu+)2to Eu3+were investigated for the first time, and varied hues from green to yellowish white and eventually to orange were generated by tuning the content of Eu3+. More importantly, a perfect white-light emission with CIE coordinates (X=0.336, Y=0.346), which are very close to the standard equal-energy white-light illuminant (X=0.333, Y=0.333), was realized in Ce3+/(Cu+)2/Eu3+codoped samples.4. Cu+/Sm3+doped borosilicate glasses:Cu+doped samples emission peaks shift to shorter wavelength with decreasing excitation wavelength for the same sample or with decreasing the content Cu+for the same excitation wavelength, which can be explained as follows:Excitated by long wavelength or in high Cu+content, Cu+located at short distance and in strong ligand field, while Cu+locate at long distance and in weak ligand field under short wavelength excitation or in low Cu+content. The efficient energy transfer process from Cu+to Sm3+were firstly investigated in Cu+/Sm3+doped samples, which also generate the varied hues from yellow white to pure white and eventually to blue white by decreasing the excitation wavelength.5. Sb3+/Mn2+doped borosilicate glasses:Upon250-340nm light excitation, the glasses exhibit broad blue emission at400nm (Sb3+) and red emission at615nm (Mn2+). The varied emitted color from blue through white and eventually to red can be obtained by properly tuning the content of Mn2+in Sb3+/Mn2+doped borosilicate glasses due to energy transfer from Sb3+to Mn2+. In addition, the emission peak of Mn2+gradually moves to longer wavelengths with increasing Mn2+content, which may be explained as follows:with increasing Mn2+content, the Mn2+-Mn2+distance is decreased, and then the interaction of Mn2+-Mn2+is enhanced. That is, the ligand field strength surrounding Mn2+is enhanced, making the excited state of Mn2+closer to its ground state and finally gives a longer wavelength emission.Our results show that Ce3+/Tb3+, Ag/Eu3+,(Cu+)2/Eu3+, Cu+/Sm3+and Sb3+/Mn2+doped silicate glasses may provide a new platform to design and fabricate novel luminescent materials for white LED in the future, further distinguish the enhancement mechanisms from different types of Ag species without doubt and made a preliminary understanding of the fluorescent properties of no rare-earth ions.