Highly emissive (with an external quantum yield exceeding 35 percent at a 365-nanometer excitation wavelength) broadband phosphors can be synthesized from a tetraalkoxysilane sol-gel precursor and a variety of organic carboxylic acids. The air-stable phosphors were synthesized at low temperatures (less than 300 degrees C) and displayed broad visible photoluminescence spectra that appeared white to the eye. Water-soluble phosphors can be prepared by the substitution of 3-aminopropyltriethoxysilane for tetraalkoxysilane in the synthesis. These materials are the most efficient extrinsic phosphors that do not contain activator metal ions.