Preparation And Luminescence Properties Of Rare Earth Ion-Doped NaLaMgWO₆ Phosphor For WLEDs

The white light-emitting diode（WLEDs）is considered to be the most promising lighting source because of its energy savings,environmental protection,small size,high brightness,fast response time,and high efficiency compared with other lighting sources.The current mainstream method to obtain white LEDs is to combine blue LEDs with yellow phosphors(YAG:Ce³⁺)to achieve white light emission.Due to the lack of a red light component,the white LEDs made by this method have the disadvantages of a high color temperature（CCT>7000K）and a low color rendering index（Ra<80）,which seriously affects their large-scale application.In this paper,a series of rare earth ions were introduced within the NaLaMgWO₆ matrix as a starting point for seeking efficient and stable phosphors for WLEDs,and the physical phase structure and luminescence properties of the prepared samples were systematically investigated,and phosphors for white LEDs with UV excitation in a single matrix were successfully prepared.The main studies are as follows:1.A series of phosphor samples of NaLaMgWO₆ co-doped with Tm³⁺and Eu³⁺were synthesized using a high-temperature solid-phase method.XRD patterns and Rietveld refinement results indicate that Tm³⁺and Eu³⁺doping does not change the monoclinic double chalcogenide structure of NaLaMgWO₆.Eu³⁺was introduced into the NaLaMgWO₆:0.04Tm³⁺phosphor sample,and the tunable spectrum from blue to red light could be achieved through the energy transfer between Tm³⁺→Eu³⁺with an energy transfer efficiency of 83.25%,and the energy transfer mechanism was confirmed as dipole-dipole interaction.2.A series of phosphor samples with Tb³⁺mono-doped and Tm³⁺,Tb³⁺and Eu³⁺co-doped with NaLaMgWO₆ were successfully synthesized using the high temperature solid phase method.For the NaLaMgWO₆ phosphor singly doped with Tb³⁺,the effects of different concentrations of Tb³⁺on the phosphor luminescence properties were discussed in detail.For phosphors of NaLaMgWO₆ co-doped with Tm³⁺,Tb³⁺and Eu³⁺ions,the luminescent color of the samples can be changed from cold white to warm white light by fixing the concentrations of Tm³⁺（5 mol%）,Tb³⁺（1 mol%）and changing the concentration of Eu³⁺,and their CIE color coordinates when the Eu³⁺concentration is 0.6 mol%are（0.3407,0.3389）.The variable temperature emission spectra showed that NaLaMgWO₆:Tm³⁺,Tb³⁺,Eu³⁺phosphors have good temperature stability,as the luminescence intensities of Tm³⁺,Tb³⁺,and Eu³⁺at 438 K were,respectively,59.6%,51.5%,and 61.4%of those at 298 K.Their thermal activation energies?E were0.21946,0.21261 and 0.22401 eV,respectively.3.A series of Tm³⁺,Tb³⁺and Eu³⁺single-doped and co-doped Na_1-xLix LaMgWO₆and Na_1-yK_yLaMgWO₆ phosphor samples were successfully prepared by the high-temperature solid-phase method.The structures,luminescence properties,and fluorescence lifetimes of the Tm³⁺,Tb³⁺and Eu³⁺single-doped Na_1-xLi_xLaMgWO₆ and Na_1-yK_yLaMgWO₆ phosphor samples were also analyzed.The results show that Li⁺and K⁺can improve the emission intensity and fluorescence lifetime of phosphors by optimizing the crystal field around rare earth ions.The thermal stability of K⁺-doped NaLaMgWO₆ phosphors was investigated,and the results showed that the introduction of K⁺effectively enhanced the thermal stability of NaLaMgWO₆:Tm³⁺,Tb³⁺,Eu³⁺phosphors.The luminescence intensities of Tm³⁺,Tb³⁺,and Eu³⁺at 438 K were 64.5%,57.4%,and 66.2%of those at 298 K.Their thermal stability was improved by 4.8%,5.9%,and 4.9%compared to the undoped samples.