| The photoluminescent properties of CaSO4 doped with Eu2+ were inverstigated in this paper. This paper concluded three parts: the valence of Eu doped in CaSO4 and the conversion between Eu3+ and Eu2+ were discussed; the influence on the structure of CaSO4:Eu phosphors and the effects of other metal ions co-doped in CaSO4 on luminescence intensity were brought out; surface modification of CaSO4:Eu was made by using autocombustion of nitrate -citrate gel processing and the polyacrylamide gel processing. Some results were obtained by means of FL, XRD, UV and so on.(1) Preparing conditions had great effects on the luminescent properties of Calcium sulfate phosphors. Raw material,pH valence, annealing temperature, annealing time and atmosphere had obvious effects on the crystal purity of Calcium sulfate host and environment of activators. Due to the radius of Eu3+ ion was close to that of Ca2+ ion, one negative vacancy could be created by the unequivalent substitution of Eu3+ for Ca2+. By thermal stimulation, electrons in these vacancies would be then transferred to Eu3+ ions. This results in the reduction of Eu3+ to Eu2+. Eu2+ created from reduction reaction would combine with a nearby O2-ion and form stable Eu-O covalent bond, in this way, Eu2+(O2-)luminescent centers were yielded. In the samples prepared by precipitation method, europium ions existed in CaSO4 host mainly in Eu2+ form.(2) Crystal configuration of the host remained unchanged if concentration of doped metal ions was small. La3+ and Y3+ were non-luminescent ions. Addition of La3+ and Y3+ could enhance the luminescent intensity of Eu2+ doped in CaSO4 with definite concentration. It was found that the unequivalent substitution between Eu2+ and La3+ or Y3+ with the help of charge compensation role of SO42- ion. Probability of unequivalent substitution between Eu2+ and Gd3+ was smaller than La3+ or Y3+, but weak energy transfer of Gd3+→Eu2+ might be observed. Ce3+→Eu2+ energy transferprocess was obvious and under the influence of temperature, owing to the Ce3+ ion was reduced to Ce2+ ion more efficiently at sites of higher symmetry(i.e. C2v) which formed with the increasing of annealing temperature, resulted from both Ce2+ and Ce3+ did not give fluorescence, reduction as well as oxidation of Ce3+ would reduce the efficient of Ce3+→Eu2+ energy transfer. Addition of alkali metal ions would decrease the luminescent intensity of Eu2+ in CaSO4, the decrease degree was Li>Na>K. The less its radius, the easier the ion entered crystal lattice. As a charge compensation role, they decrease the efficiency of Eu3+→Eu2+ transfer.(3) Nano-crystalline CaSO4:Eu might be prepared by autocombustion of nitrate -citrate gel method and the polyacrylamide gel method. The grain size of the powder was about 40 nm. Because the thermo-decomposition of citrate and polyacrylamide would improve the temperature of process, CaO would be yielded during decomposition of CaSO4, it resulted in that the emission located at 646 nm was obviously observed. We found that two processes had different effects on grain size, decomposition temperature and luminescent properties of samples... |
