Gemstones exhibit a variety of colours, such as yellow diamond, and some even glow, e.g. fluoresce, phosphoresce or both, under ultraviolet light. These optical properties often stem from impurities and defects in host crystals . Luminescent materials with bright emission have recently attracted much interest as they have wide applications , such as emitting layer materials in the light-emitting diodes (LEDs) with various wavelengths. Especially, organic materials are increasingly demanded as organic LEDs and photovoltaic devices can be thinner, lighter, inexpensive and more flexible than inorganic ones. Luminescent properties of molecules depend largely on the surrounding environment. Most luminescent dyes have π-conjugated planar structures that suffer from quenching due to self absorption and aggregation in their concentrated solutions and solid states . This hinders their applications in light-emitting diodes that require highly efficient concentrated emitters in solid states.