Y/Gd-free yellow Lu3Al5O12:Ce3+ phosphor for white LEDs

Solid solubility limit of Ce3+ ions into Lu-based garnet, Lu3(1−x)Ce3xAl5O12, was determined as below 6.7 mol% (3x<0.2 mol) through Raman spectra and X−ray diffraction patterns. Above the solid solubility limit (3x≥0.2 mol), Lu3(1−x)Ce3xAl5O12 phosphors showed the significant redshift to the yellow spectral region without Y3+ and Gd3+ ions. The redshift was explained in terms of the local compressive strain at the Ce3+ sites. The optimized sample (3x=0.4 mol) had a dominant emission wavelength of 548 nm, color coordinate of CIEx=0.421, CIEy=0.548, quantum efficiency of 80%, absorbance of 91%, lumen maintenance of 90% and high color stability at 473 K under 450 nm excitation wavelength, suggesting substitutability for the commercial yellow (Y, Gd)3(Al, Ga)5O12:Ce3+ phosphor. The measured decay times at higher Ce3+ concentration are significantly shortened at higher temperature than that of those at lower Ce3+ concentration. The yellow Lu2.6Ce0.4Al5O12 and a commercial red (Sr, Ca)AlSiN3:Eu2+ phosphor were applied to the pc-WLED, it gave an excellent luminous efficiency (138 lm/W) with a slightly lower color rendering index (Ra=76.4) under correlated color temperature of 6500 K compared to those of the (Y, Gd)3(Al, Ga)5O12:Ce3+-based one (136 lm/W, Ra=78.7). Especially, the quantities of the used phosphors were significantly decreased by 20% for the yellow LuAG:Ce and by 40% for the red (Sr, Ca)AlSiN3:Eu2+. Thus, the Y/Gd−free pure LuAG:Ce yellow phosphors can be used as alternative to the commercial yellow YAG:Ce phosphor.