What is luminescence of a material? Differentiate between fluorescence and phosphorescence.
Luminescence is the phenomenon by which a material emits light as a result of electronic excitation without a corresponding rise in temperature. It occurs when electrons in a material absorb energy from an external source such as ultraviolet radiation, X-rays, electric fields, or chemical reactions, and are promoted to higher energy states. When these excited electrons _________ _______ ___ ______ ____ _______ ___ ________ ___ ___.
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The enthalpy of vacancy formation in nickel is , and its melting point is
. What is the equilibrium vacancy concentration in nickel at
?
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