| Rare-earth phosphates have become a research focus in recent years in the field of ultraviolet-excited luminescent powders because of their outstanding merits such as lower synthesis temperatures, lower cost, fine chemical stability and thermostability, higher luminescence efficiency, etc. In this work, six series of rare-earth phosphates doped with Eu3+, Ce3+ and Tb3+ were synthesized via the solid state sintering method, XRD, FT-IR, TG-DSC, etc. were employed to characterize the products and analyze the impact of sintering temperature, and the spectral properties were analyzed in depth. This paper made the following specific tasks:(1) The optimum sintering temperatures for Ca8MgLn(PO4)7 (Ln=La3+, Gd3+, Y3+, Lu3+), CaMgP2O7 and Ca7Mg2(PO4)6 based fluorescent powders were determined to be 1200℃, 1000℃ and 900℃, respectively. The optimum sintering temperatures for SrZn2(PO4)2, Ca9Y(PO4)7 and Sr3Gd(PO4)3 based fluorescent powders were determined to be 850℃,1200℃ and 1200℃, respectively. The sintering powder curing can be effectively reduced joining cyclodextrin as medium in the process of high temperature sintering.(2) Spectral properties of Ca8MgLn1-xEux(PO4)7 (Ln=La3+, Gd3+, Y3+and Lu3+).The excitation spectrum of Ca8MgLn1-xEux(PO4)7 comprises the charge transfer band at 252nm and the excitation peaks within 4f configuration and is dominated by the former. It indicates that the excitation energy of substrate’s charge transfer state can be effectively transmitted to the activator, suggesting the contribution of substrate to the luminescence. The emission spectrum is composed of the 5D0-7FJ (J=0,1,2,3,4) transition emission peaks of Eu3+ and dominated by the 5D0-7F2 transition emission at 612nm, indicating that Eu3+ occupies the non-inversion center. The luminescent intensity changes along with the concentration of the activation ion, and the optimum doping concentration of Eu3+ in La-, Gd-, Y-and Lu-substrates were determined to be 9mol%,7mol%,5mol% and 11mol%, respectively. The Eu3+doped Ca8MgLn(PO4)7 (Ln=La3+, Gd3+, Y3+, Lu3+) fluorescent powers emit typical red lights under the excitation of ultraviolet light.(3) Spectral properties of Ca8MgLn1-xCex(PO4)7 (Ln=La3+, Gd3+, Y3+ and Lu3+).The excitation spectrum is composed of the f-d transition of Ce3+. The emission spectrum is a broad asymmetric band and can be fitted into two overlapped spectra by Gaussian function, which is attributed to the transition emissions of Ce3+ from the excited 5d state to two ground states of 2F7/2 and 2F5/2. The emission peaks of Ce3+-activated fluorescent powders are located in the ultraviolet region, suggesting that Ce3+ is a promising sensitizer. The doping concentration of Ce3+ shows impact on the emission intensity, and the optimum doping concentrations were determined to be 7mol%, 1mol%,1mol% and 7mol% for La-, Gd-, Y-and Lu-based substrates, respectively.(4) Spectral properties of Ca8MgLn1-xTbx(PO4)7 (Ln=La3+, Gd3+, Y3+ and Lu3+).The excitation spectra of the four series are all dominated by the f-d transitions of Tb3+, the emission spectra comprise the 5D3-7FJ (J=6,5,4,3) and 5D4-7FJ(J=6,5,4,3) transitions of Tb3+, and the emission intensities are related to the doping concentration of Tb3+. Along with the increase of Tb3+ concentration, both the 5D3-7FJ and 5D4-7FJ emissions increase first and then decrease, and there exists concentration quenching. The emission intensity ratio of I(5D4-7FJ)/I(5D3-7FJ) monotonically increases with the doping concentration of Tb3+, indicating that cross relaxation between SD3â†'5D4 and 7F6â†'7F0 transitions occurs when the Tb3+ concentration is big enough. Under the irradiation of ultraviolet, the samples show bright green emission.(5) Spectral properties of Ca1-xMgRexP2O7 (Re=Eu3+, Ce3+ and Tb3+)When Eu3+ is used as the activation ion, the emission is dominated by the magnetic dipole transition at 593nm, indicating that Eu3+ occupies the symmetrical center of the substrate lattice. The optimum doping concentration of Eu3+ was determined to be 9mol%. When Ce3+ is used as the activation ion, the emission peaks of all the samples are located in ultraviolet region with bimodal characteristics and energy difference of about 1951cm-1, and the optimum doping concentration of Ce3+ was determined to be 1mol%. When Ce3+ is used as the activation ion, the emission is dominated by the 5D4-7F5 transition at 543nm, and the optimum doping concentration of Tb3+ was determined to be 3mol%.(6) Spectral properties of Sr1-xRexZn2(PO4)2(Re3+=Eu3+,Ce3+,Tb3+).When Eu3+ is used as the activation ion, the emission is dominated by the magnetic dipole transition at 611nm, and the optimum doping concentration of Eu3+ was determined to be 7mol%. When Ce3+ is used as the activation ion, the emission spectrum is composed of two broad band emissions with large overlap, and the optimum doping concentration of Ce3+ was determined to be 5mol%. When Tb3+ is used as the activation ion, the emission is dominated by the 5D4-7F5 transition, and the optimum doping concentration of Tb3+ was determined to be 9mol%.(7) Spectral properties of Ca9Y1-xRex(PO4)7(Re3+=Eu3+,Ce3+,Tb3+)When Eu3+ is used as the activation ion, the emission is dominated by the magnetic dipole transition at 593nm, and the optimum doping concentration of Eu3+ was determined to be 3mol%. When Ce3+ is used as the activation ion, the emission spectrum is composed of broad band emissions with 357nm large overlap, and the optimum doping concentration of Ce3+ was determined to be 7mol%. When Tb3+ is used as the activation ion, the emission is dominated by the 5D3-7FJ transition, and the optimum doping concentration of Tb3+ was determined to be 5mol%.(8) Spectral properties of Sr3Gd1-xRex(PO4)3(Re3+=Eu3+,Ce3+,Tb3+)When Eu3+ is used as the activation ion, the emission is dominated by the 5D0-7F1 transition at 586nm, and the optimum doping concentration of Eu3+ was determined to be 9mol%. When Ce3+ is used as the activation ion, the emission spectrum is composed of two broad band emissions with two-peaks, and the optimum doping concentration of Ce3+ was determined to be 3mol%, When Tb3+ is used as the activation ion, the emission is dominated by the 5D4-7FJ transition, and the optimum doping concentration of Tb3+ was determined to be 5mol%. |
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