Preparation and optical properties of sol–gel derived thick YAG:Ce3+ phosphor film

A sol–gel process for the preparation of thick YAG:Ce3+ films has been developed. YAG:Ce3+ phosphor films with a typical yttrium aluminum garnet (YAG) photoluminescence (PL) profile were prepared successfully. Single phase YAG films with a maximum thickness of 2 μm were prepared in the present work. The refractive index of the YAG films prepared (∼1.85 @ 633 nm and ∼1.80 @ 1540 nm) was very close to that of YAG single crystal. It was confirmed that the PL efficiency of the prepared films was strongly related to the degree of YAG phase formation in the samples and the rate of YAG phase evolution strongly depended on the film thickness. To achieve high YAG:Ce3+ PL efficiency, a minimum 1.2 μm of thickness is necessary. It was also found that the optical quality of the YAG films decreased following the deposition and thermal annealing processes, probably as a result of the growth of YAG crystals inside. As an example of a compromise between high PL efficiency and good optical quality, prism coupling was achieved on a 30-layer planar waveguide sample annealed at 1000 °C for 30 min. It was proved that this sample could support multiple waveguide modes at visible wavelengths and its propagation loss at 1540 nm was estimated at 4.2 dB/cm. The temperature quenching effect in the films of the present work was also measured, being the same as that of commercial YAG:Ce3+ phosphors with relatively high Ce concentration. The present technology is intended for YAG:Ce3+ phosphor films that may be applied on white LED and it may also be of benefit to any areas where YAG films may be of interest.

► A sol–gel process for the preparation of thick YAG:Ce3+ films has been developed.
► Single phase YAG:Ce3+ films with a maximum thickness of 2 μm were prepared.
► It was found that YAG:Ce3+ PL efficiency strongly depended on the film thickness.
► The above thickness dependence was discussed and explained.
► Planar waveguide sample with high PL efficiency supports multiple waveguide modes.