A luminescent compound, comprising a phosphor group or groups and an alkylalkoxysilane, and a luminescent composition comprising such luminescent compound and a radioactive substance to provide a source of exciting radiation for the luminescent compound in the composition. The present invention further comprises a method for rendering siliceous surfaces luminescent comprising applying the compound or composition to the surface and reacting the compound or composition with water after the compound or composition has migrated into the surface to hydrolyze the compound or composition. The present invention further comprises a luminescent structure having a siliceous surface incorporating the products of the reaction between the surface, water and the compound or composition of the present invention.