Research On Rare Earth Doped GLAGG Phosphors And Ceramics

Solid-state lighting devices have the advantages of low energy consumption,environmental protection,small size,long life,fast response,high luminous efficiency,and high brightness.Among solid-state light sources,LEDs and LDs have surpassed the performance of traditional light sources（incandescent lamps and high-pressure gas discharge light sources,etc.）and have become the mainstream of the lighting market.However,most of the devices packaged with phosphors and diodes suffer from poor thermal stability and low color rendering index,which greatly limits the improvement of lighting color quality.Fluorescent ceramics have the advantages of high thermal conductivity and good chemical stability.Based on this,a series of Ce³⁺-doped(Gd_1-xLu_x)₃(Ga_1-yAl_y)₅O₁₂(GLAGG:Ce³⁺)yellow-green phosphors with the garnet structure were prepared by the molten salt method in this paper,and their structure,morphology,and luminescence properties were investigated.The fluorescent ceramic materials in the garnet system were also prepared by vacuum sintering.The study is as follows:（1）The molten salt method synthesized a series of Ce³⁺ion-doped Lu₃Al₅O₁₂ referred to as（Lu AG）,GLAGG garnet phosphors.The XRD results showed that the samples were garnet in structure.The optimum sintering process（calcination temperature and holding time）and the type of molten salt and its salt ratio were determined experimentally.The results showed that the addition of 50%Na Cl-50%Na F（at%）,a salt molar ratio of 8:1,a calcination temperature of 1350℃and a holding time of 2 h resulted in the highest purity and luminescence intensity of the prepared samples.（2）The doping concentration of Ce³⁺ions was investigated.The luminescence intensity of Gd_0.24Lu_2.7Al₄Ga O₁₂:0.06Ce³⁺phosphor samples was highest when the doping concentration was 0.06 mol and the concentration burst occurred when the doping concentration exceeded 0.06 mol.The concentration burst was due to radiation reabsorption and electric dipole-electric dipole interaction.The variable temperature spectra of the Gd_0.24Lu_2.7Al₄Ga₁O₁₂:0.06Ce³⁺phosphor were investigated and it was found that the activation energyΔE（0.163 e V）of the Gd_0.24Lu_2.7Al₄Ga O₁₂:0.06Ce³⁺phosphor sample was larger and showed good thermal fatigue resistance.（3）The effects of the Ga/Al ratio and Gd/Lu ratio on the performance of the phosphor were investigated separately.When the Ga/Al ratio was changed,the luminescence intensity reached the optimum value when Ga/Al=1/4.With the further increase of Ga³⁺doping content,the peak intensity decreased and the peak position of the luminescence spectrum showed an obvious blue shift phenomenon,with the main peak position moving from 525 nm to 500 nm.When the Gd/Lu ratio was changed,the luminescence intensity of the sample reached the maximum when the Lu content was 2.7 mol and Gd was 0.24 mol.As the Gd content increased,the luminescence intensity of the sample decreased continuously and the main peak position showed a significant red shift,from 512nm to 544nm.（4）The effect of Pr³⁺doping of rare earth ions on the performance of GLAGG:0.06Ce³⁺phosphors were investigated.The results showed that the luminescence intensity of the samples appeared to decrease with the doping of Pr³⁺.We tested the lifetime of the Ce³⁺-Pr³⁺co-doped phosphor and found that the fluorescence lifetime appeared to decrease with the doping of Pr³⁺.The energy transfer between the two was further investigated and it was found that in the GLAGG:0.06Ce³⁺,x Pr³⁺phosphor,the electric quadrupole-electric quadrupole（q-q）interaction resulted in energy transfer from Ce³⁺ions to Pr³⁺ions.（5）The effect of doping with rare earth ions Tb³⁺on the performance of GLAGG:0.06Ce³⁺phosphor was investigated.The results showed that under 438 nm excitation,the intensity of the luminescence spectra of the samples tended to increase and then decrease with the doping of Tb³⁺ions and the optimum doping concentration of Tb³⁺ions was 0.004 mol.Broadband and narrowband emission peaks appeared under 280 nm excitation and the emission intensity of Ce³⁺and Tb³⁺gradually increased with the increase of the doping amount of Tb³⁺.The former is due to the energy transfer from Tb³⁺to Ce³⁺,while the latter is mainly attributed to the increase of Tb³⁺ion content in the luminescence center.（6）Y_2.94Al₅O₁₂:0.06Ce³⁺,Gd_0.24Y_2.7Al₄Ga O₁₂:0.06Ce³⁺and Gd_0.24Lu_2.7Al₄Ga O₁₂:0.06Ce³⁺fluorescent ceramics were prepared by vacuum sintering using the best phosphors synthesized in the previous stage.The optimum sintering temperature is 1750℃and the holding time is 10h.Further extension of the holding time contributes to the increase in grain size.The type and addition of sintering aids were investigated and the results showed that the optimum doping of the sintering aids was 2 wt%for tetraethyl orthosilicate（TEOS）,0.1 wt%for Li F,0.07 wt%for Mg O and 0.03 wt%for Zr O₂.（7）The optical properties and thermal stability of Y_2.94Al₅O₁₂:0.06Ce³⁺,Gd_0.24Y_2.7Al₄Ga O₁₂:0.06Ce³⁺and Gd_0.24Lu_2.7Al₄Ga O₁₂:0.06Ce³⁺fluorescent ceramics have been investigated.We found that Y_2.94Al₅O₁₂:0.06Ce³⁺and Gd_0.24Lu_2.7Al₄Ga O₁₂:0.06Ce³⁺fluorescent ceramics have relatively good thermal stability,with fluorescence lifetimes of57.17 ns,53.76 ns,and 63.53 ns,respectively.WLED and WLD devices were packaged using the three substrate ceramics,and the LED devices corresponded to The relevant color temperatures（CCT）of the LED devices were 3522 K,4025 K,and 4277 K with color ordinates of（0.4424,0.4941）,（0.4032,0.4663）and（0.3989,0.5064）respectively.The corresponding CCTs of the LD devices at different powers are 3961 K-4009 K,3723 K-3753K,and 4565 K-4628 K.The color ordinates are shifted from（0.4062,0.4735）to（0.4082,0.4713）,（0.4119,0.4458）to（0.4136,0.4460）,（0.3778,0.4991）shifted to（0.3813,0.4993）.The results show that the three ceramics have excellent color stability and are suitable for use in color conversion materials for laser illumination.