백색 LED 응용을 위한 알루미늄 가넷계 황색형광체의 합성과 형광특성

Abstract

The color rendering index (CRI), correlated color temperature (CCT), and luminous efficiency properties of cerium doped yttrium aluminum garnet (YAG:Ce) yellow phosphors based white LEDs have been enhanced by substituting the larger radius ions (Tb3+, Gd3+, Eu3+, and Sm3+) than Y3+ ion for the dodecahedral site and substituting the larger radius ions (Ga3+, Sb3+, Y3+, Tb3+, Gd3+, and Sm3+) than Al3+ ion for the octahedral site. These aluminum garnet phosphors were synthesized by two methods. Synthetic compounds of Ce3+ doped Ln3Ga2Al3O12, Ln3Al2Al3O12, and Ln3(LnAl)Al3O12 crystalline powders have been prepared by solvothermal crystallization process at 300 ºC for 48 h. The as-prepared crystalline powders were characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra. Lattice constant values of synthetic aluminum garnet crystalline powders are larger than that of YAG:Ce and the emission wavelength shift to red. FESEM and TEM studies reveal that Ln3Ga2Al3O12 and Ln3Al2Al3O12 garnet crystalline powders were 3-dimensional star-like shaped, while, Ln3(LnAl)Al3O12 garnet crystalline powders were cubic crystalline phases and shaped as cubes with round edges having approximate diameter of about 200-400 nm. All prepared powders have been crystallized by single crystal and the growth directions are along the (100). In the second method, synthetic compounds of Ce3+ doped Ln3(YxAl2-x)Al3O12 and Ln3(SbxAlGa2-x)Al3O12 powders have been prepared by solvothermal method at 230 ºC and then calcination at 1500 ºC. Synthetic aluminum garnet particles have spherical morphology with an average size of about 2 μm which is having the good luminescent characteristics. It is important to note that, the garnet structure was not stable when the substitution of larger ions for one site either dodecahedral or octahedral sites, while the stable garnet structure was obtained by changing the amount of substitution of larger ions in both sites. The emission wavelength of aluminum garnet phosphors was shifted to the blue range by increasing the substituted to Sb3+, Ga3+, and Y3+ ion in octahedral site. While, substituting of Gd3+/Tb3+ ion in dodecahedral site resulted in red shift. The color coordination of Ce3+ doped Y3Al2Al3O12, Tb3(SbAl)Al3O12, and Gd3(SbGa)Al3O12 are (0.315, 0.341), (0.332, 0.331), and (0.337, 0.330), respectively. These results demonstrate the possibility to use Tb3(SbAl)Al3O12 and Gd3(SbGa)Al3O12 phosphors blend to enhance the white light generation in the field of white LEDs.