A flow cell for a fluorescence spectrometer includes a flow channel to receive a flow of a liquid sample, an excitation light entrance window to receive excitation light from a light source, and an emission light exit window to transmit fluorescent emission light from the liquid sample in the flow channel from the flow cell. The excitation light entrance window and/or emission light exit window includes a waveguide including: a waveguide core formed of a core material; and a cladding medium surrounding a portion of the waveguide core, wherein the cladding medium has a refractive index less than the refractive index of the core material. The waveguide defines a portion of the flow channel.