The present invention relates to a detector matrix for detecting at least one analyte in a sample, preferably a sample of a body fluid, comprising at least one enzyme active in the presence of said at least one analyte and at least one indicator reagent changing at least one optical property dependent on the activity of said enzyme, wherein said detector matrix further comprises up-converting phosphor particles, preferably UV-emitting up-converting phosphor particles. The invention further relates to a test element and a test device for detecting at least one analyte in a sample comprising the detector matrix of the invention, as well as to a method for the manufacture of a detector matrix, a method for the manufacture of a test element, and to a method for detecting an analyte in a sample, comprising contacting a detector matrix according to the invention with a sample suspected to comprise said analyte.