TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The amorphous host of (II) is in a fully-amorphous state prior to exposure to the operative environment. The amorphous host comprises an amorphous aluminum oxide based host, which comprises an amorphous yttrium aluminum oxide host or amorphous gadolinium aluminum oxide host. The amorphous yttrium aluminum oxide host comprises yttrium aluminum garnet, yttrium aluminum monoclinic and/or yttrium aluminum perovskite. The amorphous gadolinium aluminum oxide host comprises gadolinium aluminum garnet, gadolinium aluminum monoclinic and/or gadolinium aluminum perovskite. The amorphous host comprises yttrium oxide, zirconium oxide, aluminum oxide, silicon nitride or zirconium boride based materials in amorphous/glassy state. (II) comprises 0.01-40 (preferably 0.01-5) wt.% of the luminescent dopant. The luminescent dopant is a rare earth (RE) dopant, which includes lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or lutetium (Lu). The host of (II) has a first state when never having been exposed to a temperature above a predeterminable temperature and a second, different state once having been exposed to a temperature above the predeterminable temperature, and at least one luminescent dopant. (II) comprises the host, and separately, the luminescent dopant that functions to diffuse into the host when (I) is exposed to the operative, thermal environment. (II) comprises: coated particles, with a core comprising the host and a shell including the luminescent dopant, such that the luminescent dopant diffuses into the host core when exposed to the operative environment; or coated particles, with a core including the luminescent dopant and a shell comprising the host, such that the luminescent dopant diffuses into the host shell when exposed to the operative environment. (II) comprises the host that is doped with the luminescent dopant and separately a modifier agent that functions to diffuse into the host when (I) is exposed to the operative, thermal environment and thus alters the luminescence characteristic of the detection material. (II) comprises strontium aluminate (Sr4Al14O25):RE, magnesium fluorogermanate (Mg4FGeO6):Mn/RE, cerium magnesium aluminate (CeMgAl11O-19):RE, barium magnesium aluminate (BaMgAl10O17):RE, RE metaphosphate (RE(PO3)2), hydroxyapatite (Ca10(PO4)6) (fluorine, chlorine)2:antimony (Sb), manganese (Mn) or RE, (strontium, magnesium)phosphate ((Sr, Mg)3(PO4)2):tin (Sn) or RE, zinc silicate (Zn2SiO4):Mn or RE, magnesium germinate (Mg4GeO5.5F):Mn or RE, strontium borate (SrB4O7):RE, strontium borophosphate (Sr6BP5020):RE, strontium aluminate (Sr4Al14O25):RE, gadolinium (zinc, magnesium)borate (Gd(Zn, Mg)B5O10):RE, yttrium aluminum garnet (Y3Al5O12):RE, yttrium(vanadium, phosphorus, boron) (Y(V, P, B)O4):RE, yttrium, sulfur, zinc (YSZn):RE and/or aluminum oxide (Al2O3):chromium or RE or REaluminum borate (REAl3B4O12), where RE is one or more rare earth metal (preferably La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu). (II) comprises: coated particles with a core comprising the host doped with the luminescent dopant and a shell including the modifier agent, such that the modifier agent diffuses into the host core when exposed to the operative environment; or coated particles with a core including the modifier agent and a shell comprising the host doped with the luminescent dopant, such that the modifier agent diffuses into the host core when exposed to the operative environment. The modifier agent is a quenching agent that acts to decrease the luminescence of (II). The quenching agent: is the same material as the material of the luminescent dopant of (II); is a transition metal; comprises chromium, manganese, iron, cobalt, nickel, hafnium or molybdenum; or is a rare earth (preferably La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu). The modifier agent is a sensitizing agent that acts to increase the luminescence of (II) and the sensitizing agent is the rare earth.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The luminescence characteristic of (II) is an intensity of at least one emission line in measured luminescence spectrum and lifetime decay. The luminescence characteristic of (II) is measured/measurable at room temperature. The method further comprises: providing a reference material to (I), where the reference material comprises a host that is doped with at least one luminescent dopant different to that of (II); and measuring a luminescence characteristic of the reference material following exposure of (I) to the operative environment, where the luminescence characteristic of the reference material is used as a datum to the measured luminescence characteristic of (II) in determining the thermal history of (I). The host of the reference material is in a fully-crystalline state prior to exposure to the operative environment. The luminescence characteristic of the reference material is an intensity of at least one emission line in a measured luminescence spectrum and is measured at room temperature. The reference material is provided in the coating or within the body of (I). In the method, the operative, thermal environment is a high-temperature environment. Preferred Components: (II) is provided within a body of (I). In the system, the reference material is provided to (I).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: (II) is provided in a coating applied to the component, where the coating is: paint; a structural coating; or a thermal barrier coating.