Many non-luminescent chemical and biochemical analytes can be detected by luminescence (often fluorescence, but also phosphorescence) methods: cations (H⁺, alkali metal cations, alkaline earth cations, Zn²⁺, Pb²⁺, Al³⁺, Cd²⁺, Hg²⁺, etc.); anions (halide ions, citrates, carboxylates, phosphates, etc.); neutral molecules (H₂O₂, glucose, etc.); gases (O₂, CO₂, NO, etc.); biomolecules (amino acids, coenzymes, nucleosides, nucleotides, ATP, etc.); and biological macromolecules (proteins, DNA, etc.).¹  Furthermore, luminescence can provide accurate information about physical parameters such as temperature, pressure and viscosity.¹ 

A clear distinction is made here between luminescence, fluorescence and phosphorescence. Luminescence is the general word for the spontaneous emission of radiation from an electronically excited species not in thermal equilibrium with its environment. Phosphorescence and fluorescence are special types of luminescence, respectively involving and not involving a change in electron spin multiplicity in the radiative transition. In some cases (e.g., quantum dots) the spin multiplicity is not well defined, and it is better to use the term luminescence, which is always appropriate.¹  The most common type of luminescence in sensing applications is photoluminescence, which is luminescence produced by light absorption.