Lanthanide-doped glass light guides with bright luminance in the green spectral range

Dy3+ and Tb3+ single- and double-doped barium borate glasses are investigated for their luminescence properties. Their potential as luminescent light guide is evaluated on the basis of ray-tracing simulations. Transmission, photoluminescence, and quantum efficiency measurements serve as input data. The luminous flux at the end of the light guide depends significantly on its length as well as on the surface properties. The best results are obtained for light guides with the side faces coated with a 100 % reflecting mirror and a rough output face with Lambertian scattering characteristics. For an excitation wavelength of 452 nm, the color impression at the end of a Dy3+/Tb3+ double-doped light guide shifts from blue for very short light guides via white for medium-size light guides to green-yellowish for relatively long light guides.