Theoretical and experimental research on Ce:YAG crystals for use in blue laser diode illumination

The blue laser diode (LD) illuminator in this study was composed of a cerium doped yttrium aluminum garnet (Ce:YAG) crystal, a 450-nm laser diode and an optical fiber. After a first-principles calculation, the energy gap of the Ce:YAG crystal was found to be 4.71 eV, which was less than that of the YAG. The luminescent properties of the Ce:YAG were determined by the electronic distribution of the Ce (d) and Ce (f) orbits. The Ce:YAG crystal had two characteristic absorption peaks of Ce³⁺ at 332 nm and 455 nm. Hence, the 450-nm LD excited fluorescence spectra of a Ce:YAG crystal can be used for laser illumination. We discovered that the luminous efficiency of the LD increased with increasing color temperature for 4000 K, 5000 K, 6000 K and 6500 K but not for 3500 K, due to the low light transmittance of the thickest Ce:YAG crystal. The highest color-rendering index was about 70.0. Also, the blue laser without the 430-nm light from spectral radiance was, compared to an LED, a more serious eye hazard. We calculated that the permissible exposure time of the LD was longer than that of an LED. We also discovered that LD illumination is more secure than LED illumination.