Rare Earth Doped Gel Matrix Preparation And Properties Of Luminescent Materials

Using SiO₂ and TiO₂ as matrix, rare earth (Eu, Dy, Tb) single doped and co-doped xerogels luminescence material and luminescence films were prepared by sol-gel progress. The modern analysis techniques such as XRD, XPS, AFM, FT-IR, TGA-DSC, UV-visible absorption spectrum, PL and PLE spectra were used to measure the property of the luminescence material. The factors influence the luminescence property and the luminescence mechanisms of the material were studied to look for new path to prepare utility, inexpensive fluorescence material with high efficiency.1. The influence of the Boron ions and annealing temperature to the luminescence property of the Eu³+ ion were studied. The PL spectrum showed strong red emission of the material. Six emission bands were observed in the PL spectra of the samples, which is derived from the ⁵D₀->⁷F_J (J=0, 1, 2, 3, 4) transition of Eu³+,respectively. The ⁵D₀->⁷F₁ transition has splited two peaks and the strongest emission is the ⁵D₀->⁷F₂ transition(618nm)of the Eu³+,which indicated that Eu3+ is located at asymmetry center filed in Eu doped SiO₂ system. The experimental results showed that adding B ions, which reduced the symmetry of the compound environment of Eu3+ and enhanced the red emission of Eu3+, formed Si-O-B bond. The red emission intensity of Eu3+ increases with the increasing of boric acid content. The red emission intensity of Eu3+ ion has the maximum value as the xerogel annealed at 650℃. The annealing temperature mainly influenced the luminescence intensity of Eu³+ and the split degree of the transitions and has little effect on the station of the peaks.Without any premonitory process and annealed at in atmosphere, Eu2+ ions doped SiO₂ matrix xerogel luminescence material was prepared. The luminescence property and mechanism of the Eu²+ doped in SiO₂ matrix were discussed. The sample annealed at 850℃ showed a broad blue emission band of Eu2+ in the range 370nm-550nm. The emission center in the Al doped sample is located at 437nm while the center blue shifted to 423nm in the B, Al co-doped sample and the PL intensity ofthe former is almost fourfold of the latter. Only the Al doped sample has blue emission of Eu +.The emission intensity of Eu2+has maximal value when the concentration of Eu is 0.2%. The suitable mole ratio of the ingredients of the matrix is TEOS: EtOH: H2O1:2:4.2. The up conversion emission of Dy3+ was observed in Dy doped S1O2 matrix with 650nm excitation for the first time. We think that the up conversion blue/yellow luminescence near 485nm and 589nm is derived from the ESA. We find that the emission intensity of Eu2+ in the sample co-doped with Eu and Dy is higher about 90% than that of the sample single doped with Eu. A luminescence mechanism of Eu2+, which is different with the former theory, was put forward for the first time. The enhancement of the Eu2+ emission is due to the energy transfer from Dy3+ to Eu2+. Bases on the energy transfer theory, the mechanism was proved. That might to be the resonance transfer of pole interaction and the possible energy transfer path model was given.The influence of the preparation technics such as anneal temperature, anneal time, doped concentration, dried atmosphere and the components of the matrix to the luminescence property of the Eu2+ ion in the Eu, Dy co-doped S1O2 matrix were studied systematically and the luminescence mechanism was interpreted detailed. Blue emission is appeared when annealed at 700 °C and the blue emission is strongest after annealed at 900 °C . Eu2+ has strongest emission when the doped Dy3+ concentration is 0.1mol%. The Eu3+ is more easily deoxidized to Eu2+ in the sample dried in vacuum at lower temperature, because the sample dried in air need higher temperature to form network structure than the sample dried in vacuum. Only the SA and SAB matrix in four matrix xerogel annealed at 850°C had blue emission and the emission in the sample with SAB matrix wre stronger than with SA matrix. And the experiment indicated that suitable annealing time exists in the sol-gel progress of preparing the luminescence material at certain annealing temperature.3. Strong green emission peak at 543nm of 5D4-?7F5 transition of Tb3+ ions was observed in Tb doped SA matrix, the intensity was great enhanced with the increasing of the annealing temperature, which we considered that it is the consequence of theenergy transfer from SA matrix to Tb3+ ion. The Stark split of 5D4—?7Fs transition at543nm is enhanced with the increasing of the temperature.Blue emission of 5D3—>-7Fj(J=4, 5, 6)transition was not observed in the sample annealed at lower temperature( 500—700 °C) , it was ascribed to the emission intensity quench of 5D3 caused by thecross radiation between 5D3-*5D4 and 7Fo—>7F6.Eu, Tb co-doped SAB matrix tricolor luminescence material was prepared for the first time and the Tb3+—?Eu3+ electron transition in SAB matrix was discovered and studied. Red, green and blue emissions located at 618nm, 543nm and 350⁵00nm, respectively, were observed in the PL spectra of the sample annealed at 850 °C. It indicated that Eu3+, Eu2+ and Tb3+ ions existed at same time in the SAB matrix. Comparing the PL spectrum of Eu, Tb co-doped SAB and Eu single doped SAB, the blue emission was obviously enhanced in the co-doped sample. Analyzing based on the electron transfer theory showed that the blue emission enhancement was the result of the electron transfer happened between Eu3+ and Tb3+ in SAB matrix and Eu3"1"^!6) ion get a electron and become Eu2+. The suitable concentration of Tb is 0.2%.When the doping concentration was low, the emission of Eu3+ and Tb3+ were observed in the sample annealed at low temperature and the emission of Eu3+ enhanced with the increasing of Tb3+ concentration. The emission intensity of the Eu, Tb co-doped sample was four times more than that of the Eu single doped sample while the emission increasing of Tb3+ was not obvious, it is due to the energy transfer from Tb3+ to Eu3+.4. The luminescence property of the TiC>2 nano particle was studied systematically. It was discovered that the luminescence at 420nm of the free exciton, which can hardly be observed at normal temperature and the emission peak was very strong. Besides this, the strong emission peaks of nano TiC>2 are located at 453nm, 324nm, 439nm, 515nm, 474nm, 500nm and 624nm, respectively. These emission peaks derived from the luminescence of the free exciton, the tied exciton, the deficiency energy level and surface state. The luminescence intensity increased with the increasing of temperature from 250°C to 600°C and the fluorescence quench happened at 750°C.Eu doped nano TiC^ particle was prepared with TiC^, T1O2-AI2O3 and TiO as matrix. The influences of anneal temperature and matrix environment to the luminescence property were studied. The Eu3+ ions are all located in the departure state in three kinds of matrix. The strongest intensity corresponded to different annealing temperature in different matrix. The experiment showed that the Al3+ ions and B ions could enhance the luminescence intensity of Eu doped T1O2 nano particle.5. Eu doped TiC>2 luminescent films were prepared. The films surfaces were well crystallized and very smooth. The film has strong red emission of Eu at 608nm, and the emission intensity increased with the increasing of the layers from 6 layers to 9 layers and fluorescence quench happened at 10 layers. The luminescence intensity become stronger first and then decreased with the increasing of the annealing temperature and the films annealed at 600°C have strongest emission intensity..Eu doped SiC>2 luminescence films was prepared. The film has emission of 5Do—* 7F2 transition of Eu3+ at 615nm. Compared with the PL spectra of the xerogel, in the film Eu located at the state with much lower symmetry. The emission intensity enhanced with the increasing of the concentration, it indicated that concentration quench had not happened when the Eu3+ concentration was in the range 0.2%^l .4%.Eu, Dy co-doped SiC>2 matrix blue emission films were prepared. The PL spectrum of the film shows that the film has rather strong blue emission at 436nm, which is due to the f-d transition of Eu2+.Eu, Tb co-doping for the first time, prepared single substrate rare earth co-doped S1O2 matrix tricolor luminescence film. It was discovered that Eu3+, Tb3+ and Eu2+ existed in the sample annealed at 850 °C, the PL spectra showed red, green and blue emission at 615nm, 543nm and 480nm, respectively.