Study On Luminescent Properties Of Rare Earth Co-doped Phosphates Phosphors

White light-emitting diodes (w-LEDs) are the promising new emitting light sourcefor common illumination based on the advantages of long lifetime, environmentalfriendliness and energy saving, which are regarded as the fourth generation solid-statelight. Therefore, the current academic interests in white light are displaced bypursuing single-component white-light phosphors. Rare earth Dy3+ions have twodominant emission bands in the blue region (470–500nm) due to4F9/2â†'6H13/2transition and in the yellow region (560–600nm) due to4F9/2â†'6H15/2transition. It ispossible to achieve near white light emission by adjusting the yellow to blue intensityratio value. In this paper, the photoluminescence properties of emission-tunablephosphors were studied and the energy transfer in between Tm3+and Dy3+wasobserved. The results suggest that those phosphors might be used as a potential singlephase phosphors for UV-based w-LEDs.First of all, The La7(1-x)P3O18:xDy3+phosphors were synthesized by hightemperature solid-state reaction. The emission peaks of La7(1-x)P3O18:xDy3+wererespectively480nm,578nm,664nm, corresponding to the4F9/2â†'6H15/2,6H13/2and6H11/2transition of Dy3+energy level under347nm excitation. The chromaticitycoordinates of La7(1-x)P3O18:xDy3+are close to white light point (x=0.33, y=0.33). TheDy3+concentration corresponding to the maximal emission intensity is2mol%.According to D.L. Dexter theory, the concentration quenching mechanisms are the d-dinteraction.Secondly, The Sr3Y1-x(PO4)3:xDy3+Powder samples were synthesized by solid-statereaction method. The PL and PLE spectra showed that the phosphor could be excitedby light from350to460nm and two strong peaks centered at484nm and576nmcorresponding to the4F9/2â†'6H15/2transition and the4F9/2â†'6H13/2transition.According to the Dexter’s theory, it was found that the major mechanism forconcentration quenching as a result of dipole–dipole (d–d) interaction. Thechromaticity coordinates of Sr3Y1-x(PO4)3:xDy3+phosphors are close to the whitecolor chromaticity coordinates (x=0.33, y=0.33). These results indicate that theSr3Y1-x(PO4)3:xDy3+phosphor may be a promising single-component phosphor in thefield of white LEDs. And then, Powder samples Sr3Y1-x-y(PO4)3:xTm3+-yDy3+were synthesized byconventional solid-state reaction method. By appropriate tuning of activator content,the emission color can be adjusted around blue to white and yellow. It was discoveredthat the energy transfer from Tm3+to Dy3+was demonstrated to be via the intensity ofDy3+emission increase with the increase of Tm3+concentration. By changing thedoping concentration of Tm3+and Dy3+in Sr3Y(PO4)3, white-emitting phosphors areproduced by350nm excitation wavelength, their corresponding color coordinates arevery close to the white color chromaticity coordinates (x=0.33, y=0.33). Therefore,Sr3Y1-x-y(PO4)3:xTm3+-yDy3+phosphors could be a good promising single-componentwhite light-emitting UV-convertible phosphor in the feld of white EDs.Dy3+/Tm3+single doped and co-doped La3PO7phosphors were synthesized by solidstate reaction method. The single doped Dy3+/Tm3+ions showed their characteristicemissions yellow and blue. The luminescence intensity of this phosphor frstlyincreased and then decreased with increasing concentration of Dy3+ions. Theexperimental results and the theoretical calculation indicate that the concentrationquenching mechanism of Dy3+ions in La3PO7is the dipole–dipole interaction. Bychanging the doping concentration of Dy3+and Tm3+in La3PO7, their correspondingcolor coordinates are very close to the white color chromaticity coordinates (x=0.33,y=0.33). These results indicate that the La3-x-yPO7:xDy3+-yTm3+phosphors exhibitgreat potential for use as single-component phosphors for w-LEDs.Finally, Powder samples Ba3La1-x(PO4)3:xEu2+have been fabricated by hightemperature solid-state reaction method at1200°C in CO atmosphere. The PLE andPL spectra show that this phosphor can be excited efficiently by UV light from280to400nm and emits intensely blue light. The quenching concentration ofBa3La1-x(PO4)3:xEu2+is0.015mol, According to the theoretical calculation, the majormechanism for concentration quenching is dipole–dipole(d–d) interaction.