The unique properties of colloidal semiconductor nanocrystals, or quantum dots, have attracted enormous interest in a wide range of applications, including energy, lighting, and biomedical fields. However, widespread implementation is hampered by the difficulty of developing large-scale and inexpensive synthesis routes, mainly due to our limited knowledge of formation reaction parameters. We report here a simple yet powerful method to experimentally determine critically important reaction parameters such as rate constants, activation barriers, equilibrium constants and reaction enthalpies. This method was applied to wurtzite cadmium selenide nanocrystals, yielding activation energies for growth and dissolution of 14 ± 6 kJ mol–1 and 27 ± 8 kJ mol–1, respectively, and a reaction enthalpy for nanocrystal growth of −15 ± 7 kJ mol–1. Moreover, the Gibbs free energy for growth was found to be negative at low temperatures, whereas dissolution becomes the spontaneous process above 150 °C.

A mix-and-match sol–gel deposition method allows fabrication of one-dimensional photonic bandgap materials with strategically placed porous layers. Examples of fabricated optical devices include a Bragg mirror with an ultra-high refractive index difference, an all-silica optical reflection switch and a porous Fabry–Perot microcavity with excellent relative humidity sensing ability.

A mix-and-match sol–gel deposition method allows fabrication of one-dimensional photonic bandgap materials with strategically placed porous layers. Examples of fabricated optical devices include a Bragg mirror with an ultra-high refractive index difference, an all-silica optical reflection switch and a porous Fabry–Perot microcavity with excellent relative humidity sensing ability.