Preparation And Luminesence Properties Of Rare Earth Doped Ba₂SrWo₆ Phosphors

White light-emitting diodes?LEDs?have attracted much interest due to its advantages in light efficiency,energy consumption,service longevity and environmental conservation.Currently,there are three principle strategies to produce white light from LEDs: combining multiple LED chips with three kinds of colors in a single device,which brings complex main circuit,high cost;employing a blue LED with YAG: Ce³⁺ yellow phosphors,this method is very simple and has the highest efficiency;adopting an ultraviolet LED chip to excite red,green,and blue phosphors or a single-phase phosphor,unfortunately,compared with blue and green phosphor,the luminescence efficiency of red-emitting phosphor excited by ultraviolet or near ultraviolet is still unsatisfied.In addition,up-conversion luminescent materials doped rare-earth(RE³⁺)ions,which can convert a low frequency excitation into a high frequency emission,emitting green and red upconversion emissions.Promising applications include solid-state lasers,three dimensional display,fluorescence labeling,detection,anti-fake,and so on.In order to take advantage of up-conversion luminescent materials to apply to more domains,this topic are worth our attention and discussion based on hereinbefore problems,this papermainly complete hereinafter work:?1?developing yellow phosphors that can be efficiently excited by NUV/blue light,?2?preparing red phosphors that can be efficiently excited by UV light,?3?synthesizing Yb³⁺/Er³⁺ co-doped UC luminescent phosphors.In this paper,we choose tungstates that possess the double perovskite structure as host luminophores because of their special chemical and physical properties.Furthermore,a series of phosphor was synthesized through a high temperature solid-state reaction method.Details are as follows:?1?Ba₂SrWO₆ yellow phosphor was synthesized by a high temperature solid-state reaction method through CO reducing atmosphere.The powder X-ray diffraction?XRD?and EDS were employed to characterize the as-prepared phosphors.All of the profiles match well with the Standard file,which indicating that pure phase of Ba₂SrWO₆ can be obtained by this way.It can be observed that the excitation spectrum contains a strong broad band from330-480 nm by monitoring the emission at 602 nm and the emission band under the excitation of 397 nm shows a broad yellow emission.Its CIE chromaticity coordinates are calculated as x=0.550,y= 0.442.According the EDS,one explanation for this might be attributed to the carbon impurities in the Ba₂SrWO₆ samples.Moreover,the WLED can be fabricated by the combination of a blue LED chip and yellow-emitting phosphor.?2?Eu³⁺-doped Ba₂SrWO₆ red phosphor was synthesized through a high temperature solid-state reaction method.The optical band gap was calculatedthrough the UV-diffuse reflectance spectrum.Under the excitation of UV light?312nm?,the as-prepared phosphors exhibit intense red luminescence originating from the characteristic transitions of Eu³⁺ ions and the optimal doping concentration is 15 mol%.The ????=2 and 4?intensity parameters was calculated according to Judd-Ofelt theory.The color purity was been calculated,which is better than that of the commercial red phosphors Y2O2S:Eu³⁺.?3?Sm³⁺-doped Ba₂SrWO₆ red phosphor was also synthesized through a high temperature solid-state reaction method.Under the excitation of UV light?316 nm?,the as-prepared phosphors exhibit intense red luminescence originating from the characteristic transitions of Sm³⁺ ions and the optimal doping concentration is 2.5 mol%,the energy transfer type among Sm³⁺ ions in Ba₂SrWO₆ phosphors is exchange interaction by theoretical calculation.?4?Er³⁺/Yb³⁺-codoped Ba₂SrWO₆ phosphor was synthesized through a high temperature solid-state reaction method for the first time.The phases and upconversion luminescence properties were characterized by X-ray diffraction and upconversion luminescence spectra,respectively.When the Yb³⁺ ions concentration was 10 mol%,the maximal intensity can be achieved at the Er³⁺ions concentration of 5 mol%.Moreover,two-photon process was deduced to be main mechanism for green and red upconversion luminescence by the analysis of power-dependent upconversion luminescence intensity.