Study On Spectral Continuous Adjustment Of Phosphate Fluorescent Materials For White LED

White light-emitting diodes (LED) are considered as the most promising light source for solid state lighting due to their low power consumption, long lifetime and environment benefits after conventional incandescent and fluorescent lamps. At present, the commercial method of generating white light is the combination of blue LED chip with the famous yellow phosphor, Y3Al5O12:Ce3+(YAG:Ce3+). However, this method leads to a low color-rendering index and high correlated color temperature of white light due to the lack of red light. In order to solve this problem, another way of combining ultraviolet (UV) LED chips with tricolor phosphors was developed and highly favored. The luminescence properties of the phosphors used can strongly affect eventual performance of white light LED devices. Therefore, the exploration of excellent tri-color phosphor materials plays an important role in the development of w-LEDs.Phosphate is very fit for phosphor host materials owing to their easy synthesis, stable chemical property and low cost. Therefore, two type phosphates are selected as our host materials and we explored the synthesis conditions for hosts by solid state reaction, investigated luminous properties and energy transfer process of different rare earth ions doped in hosts. Our work provides some new research ideas for UV-converted phosphors applied in w-LEDs.In this paper, we prepared three novel phosphate phosphors by high temperature solid state reaction:K3Gd(PO4)2:RE (RE=Tb3+, Ce3+/Tb3+), KCaY(PO4)2:RE (RE=Ce3+/Tb3+), K3Gd(PO4)2:RE (RE=Tb3+/Eu3+). We investigated their luminous performances under UV light irradiation and focused on how to utilize energy transfer between co-doped rare earth ions and adjust concentration to achieve tunable emission color. The main research contents are listed below:Firstly, A series of K3Gd(PO4)2:Ce3+, Tb3+phosphors were synthesized by solid-sate reaction method. The emission spectra of K3Gd(PO4)2:Tb3+exhibit the typical emissions of Tb3+. It is noted that concentration quenching of Tb3+can’t be observed in K3Gd(PO4)2:Tb3+. The reason is that the average shortest distance of Tb3+-Tb3+in K3Gd(PO4)2:Tb3+is relatively long that energy transfer between Tb3+-Tb3+ions can’t take place effectively. Co-doping of Ce3+enhances the emission intensity of Tb3+greatly through an efficient energy transfer process from Ce3+to Tb3+. The energy transfer was confirmed by photoluminescence spectra and decay time curves analysis. The efficiency and mechanism of energy transfer were investigated carefully. Moreover, due to the non-concentration quenching property of K3Tb(PO4)2, the photoluminescence spectra of K3Tb1-x(PO4)2:xCe3+were studied and the results shows that when x=0.11the strongest Tb3+green emission can be realized.Secondly, A series of new luminescence emission-tunable phosphors KCaY(PO4)2:0.03Ce3+,yTb3+have been synthesized by high temperature solid-state reaction method. Under ultraviolet light excitation, KCaY(PO4)2:0.03Ce3+,yTb3+can achieve tunable emission from deep blue to yellowish-green by changing the concentration of Tb3+. The efficient energy transfer process from Ce3+to Tb3+ions was observed and confirmed in terms of corresponding excitation, emission spectra and photoluminescence decay curves, which the efficiency is above80%. In addition, the energy transfer mechanism from Ce3+to Tb3+was proved to be dipole-dipole interaction. By utilizing the principle of energy transfer and appropriate tuning of Ce3+/Tb3+contents, KCaY(PO4)2:0.03Ce3+,yTb3+can realize emission color tunableThirdly, An-UV convertible phosphor K3Gd(PO4)2:Tb3+,Eu3+with tunable-emitting color has been synthesized by the solid state reaction. Under the Tb3+excitation (373nm), the Eu3+emissions increase dramatically with increasing the Eu3+content due to the efficient energy transfer from Tb3+to Eu3+, which has been justified through the luminescence spectra and fluorescence decay curves. K.3Gd(PO4)2:0.5Tb3+, yEu3+can achieve tunable color emissions from yellowish-green through orange-yellow and ultimately to reddish-orange by simply adjusting the Eu3+content. In addition, the energy transfer mechanism was demonstrated to be the dipole-dipole interaction and the energy transfer efficiency was can be up to97.3%.