Preparation And Regulation Of Broadband Blue Emitting Phosphors Activated By Rare Earth Ions

Besides energy saving and environmental protection,white light emitting diode（wLED）also has the advantages of high luminous efficiency and long service life,which is in line with the concept of“green development”.Therefore,it is used to replace traditional fluorescent lamps and incandescent lamps.The main commercial way to obtain wLED is to use In Ga N blue chip（440-470 nm）to combine Y₃Al₅O₁₂:Ce³⁺yellow phosphors.However,due to the lack of red light in the spectrum,the wLED obtained by this way has the disadvantages of high correlated color temperature（CCT）and low color rendering index（CRI）,which restricts its application in indoor lighting.So researchers suggest some ways to improve these issues,mainly including:（a）adding proper phosphors with red light emission to the above methods;（b）adding red phosphor,green phosphor instead of Y₃Al₅O₁₂:Ce³⁺;（c）using a/an（near）-UV LED chip to excite red,green and blue three-color phosphors;（d）combining a/an（near）-UV LED chip with a white-emitting phosphor.The key to obtain wLED with high light efficiency,low CCT and high CRI,is to synthesize phosphors with high quantum efficiency（QE）and good thermal stability.On the basis of this goal,a series of phosphors were synthesized using Sr₃Y₂（BO₃）₄and K-β-Al₂O₃ as host and Ce³⁺,Eu²⁺as activators.The main findings are as follows:1.Solid solution phosphors(Ba_1-xSr_x)₃Y₂（BO₃）₄:Ce³⁺were synthesized by conventional solid-state reaction.The phosphor shows a wide blue emission band at about 420 nm with a shoulder at around 500 nm.The emission intensity and QE gradually enhance from Ba₃Y₂（BO₃）₄:Ce³⁺to Sr₃Y₂（BO₃）₄:Ce³⁺in this solid solution series,among which Sr₃Y₂（BO₃）₄:Ce³⁺has the highest internal（92.7%）and external（66.8%）QE.However,the thermal stability need to be improved.The refinement of the crystal structure indicates that strontium-rich samples have higher structural rigidity than barium-rich ones,which is also the reason for the difference in QE and thermal stability.The wLED fabricated with Sr₃Y₂（BO₃）₄:Ce³⁺has a high CRI value.2.An highly efficient and zero-thermal-quenching blue-emitting phosphor is realized in nominal K_m-0.4Al₁₁O_17+δ:0.2Eu²⁺,which benefits from rigid aluminate structure with space group P6₃/mmc and the introduction of trap energy levels.The internal and external QE of optimal nominal K_1.6Al₁₁O_17+δ:0.2Eu²⁺are 97.1%and 61.8%,respectively.The phosphor exhibits zero-thermal-quenching behavior within 150°C.Further increasing K content results in even better thermal stability,however,lower QE.The relationship between luminescence properties and crystal structure was discussed.Results suggest that the blue-emitting phosphor is a candidate for phosphor converted wLED based on near-UV or violet chip.3.On the basis of K-β-Al₂O₃,Na atoms were introduced to replace K atoms,and a series of solid solution phosphors K_1.6-yNa_yAl₁₁O₁₇₊d:0.2Eu²⁺（y=0-1.6）were synthesized.The intermediate component KNa_0.6Al₁₁O₁₇₊d:0.2Eu²⁺has the highest emission intensity.With the increase of y value,the strongest emission peak gradually redshifts from448 nm to 464 nm.The phosphor exhibits zero-thermal-quenching within25-150°C or 25-200°C,and the internal QE of all samples are greater than 84%.The wLEDs made with the y=0.6 sample all showed good performance.This results indicate that the blue phosphor has certain application potential in the phosphor converted wLED.