Composite wavelength converter

A white LED light source comprising an LED (100) and a composite wavelength converter (1) mounted on a light emitting surface of the LED (100), the converter (1) converting at least a portion of light having a wavelength lying within a first range emitted by the LED (100) into light having a wavelength lying in a second range, wherein the wavelength lying within the second range is higher than the wavelength lying within the first range

• the composite wavelength converter comprising
• a substrate (10) formed by a first layer of single crystalline garnet phosphor presenting first emission and excitation spectra, having a cubic crystal structure, a first lattice parameter and oriented crystal planes, wherein the substrate (10) contains a first activator, and
• an epitaxial film (20) formed by liquid phase epitaxy on the top and bottom of the substrate (10) as a second layer of single crystalline garnet phosphor with the first activator, presenting second emission and excitation spectra, having a cubic crystal structure and a second lattice parameter, wherein the epitaxial film (20) is arranged directly on the top and bottom of the substrate (10) on the oriented crystalline planes of the substrate (10),
• wherein the second emission and excitation spectra are different from the first emission and excitation spectra,
• wherein the difference between the first lattice parameter and the second lattice parameter results in a lattice mismatch within a range of −2.0 to +2.0%, and
• wherein the thickness of the epitaxial film (20) on the top of the substrate (10) is at least 2 μm, and the thickness of the epitaxial film (20) on the bottom of the substrate (10) is at least 2 μm.