Ba₅?PO₄?₃F:Eu³⁺/Tb³⁺/Tm³⁺ Phosphors And CaWO₄:Eu³⁺/Tb³⁺/Tm³⁺ Doped Lithium Ion Photoluminescence Characteristics

As the new generation of lighting source,LED is of many advantages,such as high luminous efficiency,long service life,energy-saving and pollution-free,high color rendering index,low production cost,and so on,therefore it has comprehensive application prospect.It is one of the hot topics to further improve the luminous efficiency of LED,especially to explore a new type of phosphor for white LED,which not only has important scientific significance but also presents great application value.In this thesis,two series and three kinds of phosphors doped rare earth ions are prepared.The photoluminescence characteristics are studied,and color coordinates and color temperature are also discussed.The aim of the our investigation is trying to find a sort of new white LED phosphors with low phonon energy,high luminous efficiency and good stability.The specific works are as follow:First,a series of Ba₅?PO₄?₃F:Eu³⁺phosphors have been prepared by high temperature solid phase method,and the excitation and emission spectra of the samples are measured,respectively.Intense emissions with central wavelength at 577,591,615 and 658 nm can be obtained,corresponding to 5D0?7F0,1,2,3 transitions of europium ion.The optimal doping concentration is 80 mol%.The influence of different positions of crucibles in the high temperature furnace on the photoluminescence intensity is analyzed.The results show that,because the temperature on both sides of the furnace is higher than that in the middle,the volatilization of NH4 F raw material in the crucible located at the both-side is faster,which reduces the proportion of fluorine elements and causes the weakness on the luminous intensity of phosphors.Secondly,a series of Ba₅?PO₄?₃F phosphors single-doped with terbium,thulium and doubly-doped europium and terbium as well as triply-doped europium,terbium and thulium are prepared by the same high-temperature solid phase method.There exists strong 545 nm green emission from the single-doped terbium sample,and it is due to 5D4?7F5 transition of Tb³⁺ion.The optimized concentration is 0.3 mol%.According to Dexter theory,the concentration quenching mechanism is discussed and the results show that the quenching is caused by the electric dipole-electric dipole interaction.The characteristic emission?454 nm?of sample doped thulium ions originates from the 1D2?3F4 transition,and the optimized concentration is 0.9 mol%.With the increase of Eu³⁺concentration in doubly-and triply-doped phosphors,the characteristic emission of Eu³⁺ ion becomes intense,however,the characteristic emission of Tb³⁺ and Tm³⁺ ion are weakened.The energy transfer mechanismsof Tb³⁺?Eu³⁺and Tm³⁺?Eu³⁺are analyzed by combining measurement results of the lifetime.The color coordinate of Ba₅?PO₄?₃:0.7Eu³⁺/0.3Tb³⁺/0.7Tm³⁺ is?0.325,0.336?and the color temperature is 5842 K,which is very close to the standard white light?0.333,0.333?.Finally,series CaWO₄ phosphors doubly-and triply-doped Eu³⁺,Tb³⁺ and Tm³⁺ ions are prepared by the same technique,and lithium ion is codoped.The characteristic emission of Eu³⁺ ion in Eu³⁺and Tb³⁺ doubly-doped phosphors enhances firstly and then weakens with the increase of Tb³⁺doping concentration,which further proves the energy transfer between Tb³⁺and Eu³⁺ ions.In the triply-doped samples of europium,terbium and thulium,the characteristic emissions of terbium ion and europium ion enhance firstly and then weaken with the increase of thulium concentration,still indicating that there exist energy transfer of Tm³⁺?Tb³⁺and Tm³⁺?Eu³⁺.In particular,the charge is balanced after adding Li+ions which results in that the lattice defects are weakened and the photoluminescence intensity of CaWO₄ phosphors co-doped Eu³⁺,Tb³⁺ and Tm³⁺ ions is improved significantly.