| Diode was invented for nearly a century,and it has been used as a lighting product for daily use in the last decade or two.It turns out that LED will be the main lighting source in the 21st century to replace the traditional incandescent lamp and other products to achieve a more efficient and energy-saving lighting experience.However,there are still many problems need to be solved in the application of LEDs to achieve better energy efficiency.At present,the most promising method to achieve white LEDs is to excite trichromatic phosphors through UV diodes.This method has advantages such as:simple process,low cost,high color rendering and high efficiency compared to conventional blue light excitation.Tungstate has stable physical and chemical properties,and the temperature of the synthesis process is not high.It is suitable as a substrate for luminescent materials excited by ultraviolet energy.Previous studies have shown that hydrothermal method is a very effective synthesis method.Samples prepared by hydrothermal method showed better performance than that of samples prepared by the conventional high temperature method.Therefore,hydrothermal method was used to prepare rare earth doped CaGd2(WO4)4 for white LEDs applications.X-ray diffraction,scanning electron microscopy and fluorescence spectrometer were used to characterize the properties of samples.The results are as follows:1.CaGd2(WO4)4:Eu3+was prepared by hydrothermal method with appropriate conditions.XRD and data show that the prepared sample has a scheelite structure of CaGd2(WO4)4.The sample has a sheet morohology.The excitation spectrum shows that the sample has strong absorption in the near ultraviolet region(394 nm)and the blue region(466 nm).The emission spectra show that the strongest emission peak of the sample is at 616 nm.It can be seen from the emission intensity that near-ultraviolet excitation is greater than blue light excitation,indicating that phosphors are more suitable for near-ultraviolet excitation.2.The effects of different conditions on the luminescence properties of CaGd2(WO4)4:Eu3+phosphors were studied.It was found that when the pH is 9.0,the prepared sample has a scheelite structure of CaGd2(WO4)4 and the sample morphology is a sheet-like structure.When the hydrothermal temperature is 210℃,the fluorescence performance is the strongest.When the hydrothermal reaction time is 15 h,the emission intensity reached the maximum.When concentration of Eu3+ion is 0.7 mol,the best performance is obtained.When the concentration of Eu3+ion exceeds 0.7 mol,the emission intensity decreases due to concentration quenching.3.The CaGd2(WO4)4:Tb3+phosphor was successfully prepared by hydrothermal method.The strongest emission peak of the sample was 546 nm under 377 nm UV excitation.The effect of different concentration of Tb3+ ion on the luminescence intensity of the sample was studied.The results show that the emission intensity of the sample reaches the maximum when the concentration of Tb3+ ion is 0.7 mol,and the emission intensity decreases when the concentration of Tb3+ion exceeds 0.7 mol due to concentration quenching.Samples co-doped with Tb3+and Eu3+ions were studied,and it was found that the characteristic emission peaks of Tb3+ions and Eu3+ions were observed simultaneously at the excitation of 377 nm.With the increasing of Eu3+ ions concentration,the intensity of the characteristic emission peak at 616 nm attributed to Eu3+ions is continuously enhanced,while the intensity of the 546 nm emission peak of Tb3+ ions is significantly reduced.Under the excitation wavelength of 377 nm and the emission wavelength of 546 nm,it is found that the lifetime decay of the co-doped sample shows obvious attenuation,which proves the energy transfer of Tb3+to Eu3+.The energy transfer efficiency is as high as 78.7%. |
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