A light-emitting device includes a substrate, a semiconductor diode structure, a wavelength-converting layer less than 50. microns thick with luminescent particles in an index-matched inorganic binder, optical sidewall coating, and an optical sidewall structure. The optical sidewall structure is interposed between substrate sidewalls and optical sidewall coating, and redirects side-propagating output light toward or within the wavelength-converting layer. The optical sidewall structure can be part of the wavelength-converting layer or part of an adhering layer between the substrate and the wavelength-converting layer.