Synthesis And Luminescent Properties Of Highly Efficient And Thermally Stable Silicate/aluminate Phosphors

Phosphor-converted white light-emitting diodes?white pc-LEDs?are utilized as solid-state lighting sources all over the world because of their advantages such as low power consumption,long operation time,environmental friendliness,and so forth.The most common strategy for white pc-LEDs is to combine the yellow-emitting phosphor Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)with a blue LED chip.However,this combination usually has a highly correlated color temperature?>4500 K?and a poor color-rendering index?CRI,Ra<80?because of the lack of a red-emitting component.A simple way to solve these drawbacks is the addition of a red-emitting phosphor.An alternative strategy to achieve warm white light with a high CRI value is by combining blue-,green-,and red-emitting phosphors with a near-UV LED chip.Phosphors should have suitable excitation and emission bands when utilized in pc-LEDs,which can match the emission peak of the LED chip and realize good performance of illumination,respectively.Furthermore,high quantum efficiency and good thermal stability are the other two important parameters.In this paper,Ba_2-x-x Sr_xSiO₄:Ce³⁺and(Ba_0.8Eu_0.2O)?Al₂O₃?_4.575×?1+x?were selected as the research objects,highly efficient and thermally stable bluePhosphorthroughStructuralmodification.Ba_1.8-xSr_xSiO₄:0.1Ce³⁺,0.1Na⁺?x=0-1.8?phosphors were prepared by a high-temperaturesolid-statereaction.Theemissionpeaksof Ba_1.8-xSr_xSiO₄:0.1Ce³⁺,0.1Na⁺shift from 391 to 411 nm with increasing Sr²⁺content under excitation by a UV light at around 360 nm.Ba_0.4Sr_1.4SiO₄:0.1Ce³⁺,0.1Na⁺phosphor exhibits the best performance of luminescence,whose absolute quantum efficiency is 97.2%,and the emission intensity at 150°C remains 90%of that at room temperature.The effect of replacing Ba²⁺by Sr²⁺on the red shift of the emission band and the increase of quantum efficiency and thermal stability was investigated in detail based on the Rietveld refinements,Raman spectra,thermoluminescence,and decay curves,etc.The performance of UV chip-based pc-LEDs indicates that Ba_0.4Sr_1.4SiO₄:0.1Ce³⁺,0.1Na⁺can be a promising blue phosphor for white-emitting pc-LEDs.In this work,the crystal structure and luminescent properties of Eu²⁺-activatedaluminatephosphorswithanormalcomposition(Ba_0.8Eu_0.2O)?Al₂O₃?_4.575×?1+x?(short for BA_1+xO:0.2Eu²⁺)were studied.Although the crystal structures of BA_1+x+x O:0.2Eu²⁺have a same space group,the increase of the Al content will lead to the decrease of cell volume,occupancy of Ba and O6 that is at around Ba?I?site,and the increase of the average distance between Eu²⁺ions,which are responsible for the modification of luminescent properties.BA_1+x+x O:0.2Eu²⁺exhibits a blue-green emission with an emission peak at around 450 nm and a shoulder at around 490 nm.The increase of Al/?BaEu?ratio results in the increase of both absolute QE and thermal stability.The absolute QE of BA_1.5O:0.2Eu²⁺is 99.4%,and the emission intensity at 150°C remains more than 90%of that at room temperature,showing the best performance.Furthermore,all of the external QE values of BA_1+xO:0.2Eu²⁺?x=0.2-0.5?are higher than 70%.The properties of the LEDs based on the as-prepared phosphor suggest its potential as a candidate for UV LED pumped phosphor-converted white LEDs.