Synthesis And Photoluminescence Properties Of Silicate Phosphors For White-LEDs

Recent years,white light-emitting-diodes(w-LEDs)have caught much attention due to their excellent properties,such as small volume,long lifetime,energy saving and environmental friendly products.W-LEDs are considered to be the next-generation lighting.At present,the most common way to generate white light is phosphor conversion method.The industrial performance of w-LEDs,such as color rendering index(CRI),correlated color temperature(CCT)and energy utilization efficiency,is closely linked with phosphors.Hence,it is very important to develop new kinds of phosphors for demands.Moreover,the structure of host materials has a great influence on the properties of phosphors.Improving the performance of existing phosphors by structure characteristics has a guiding significance for the future exploration.Silicate compounds have advantages of highly physical and chemical stability,abundant resources and diverse structures.They are ideal host materials for w-LEDs application.In our study,we focus on three silicate compounds,namely,Na2CaSi2O6,K2MgSi3O8 and Na1.8Mg0.9Si1.1O4,and successfully tune the luminescent properties of phosphors by host modification and energy transfer mechanism of two rare earth ions.The main contents are as follows:1.We synthesized Na2CaSi2O6:Ge3+ blue-emitting phosphors by solid state reactions and measured its external quantum efficiency.Furthermore,we introduced Sr2+ in 4a2CaSi2O6:Ce3+ to tune the properties of phosphors.Rietveld refinements clarified preferable occupancy of Sr2+ in Na2CaSi2O6 compound,which results in the asynchronous expanding of two sites of M3 and M4.With the increase of Sr2+ concentration,Ce3+migrate between these two sites.This phenomenon also reflects in the irregular variation of PL and PLE spectra.2.We synthesized Na2CaSi2O6:Eu3+ red-emitting phosphors by solid state reactions and studied the influence of charge compensator on the luminescence of phosphors.We also explained why Eu2+ cannot exist stably in Na2CaSi2p6(compound by energy band theory.3.We synthesized K2MgSi3O8:Eu2+ green-emitting phosphor by solid state reaction and obtained the crystal structure of K2MgSi3O8 by Rietveld refinement.Refinement results proved that there remains only one K+ site in K2MgSi3O8.When Eu2+ substitute K+in parent structure,it should generate K+ vacancies to compensate the charge difference.This phenomenon leads to multiple Eu2+ sites in K2MgSi3O8:Eu2+ samples.4.We synthesized K2MgSi3O8:Ce3+ blue-emitting phosphors by solid state reactions.Similarly,Ce3+ replacing K+ result in multiple Ce3+ emissions in K2MgSi3O8:Ce3+phosphors.We further synthesized K2MgSi3O8:Ce3+,Tb3+ samples,and energy transfer occurred from Ce3+ to Tb3+.With the increasing Tb3+ content,the emission can be tuned from blue to greenish blue.The energy transfer efficiency can reach the maximum of 51%when Tb3+ concentration is y=0.09.5.We synthesized Nai.8Mg0.9Si1.1O4:Ce3+ phosphors by solid state reactions.The emission spectrum of Na1.8Mg0.9Si1.1O4:Ce3+ cover the near-ultraviolet and blue region.Furtherly,we synthesized Na1.8Mg0.9Si1.1O4:Ce3+,Tb3+ phosphors and revealed the efficient energy transfer from Ce3+ to Tb3+.We also studied the luminous efficiency of Na1.8Mg0.9Si1.1O4:Ce3+,Tb3+.