• Yuhei MiyauchiEmail author


Spontaneous emission (radiation) of light from an electronically excited material (except for thermal radiation) is called “luminescence.” In particular, photoluminescence (PL) is light emission occurring after absorption of shorter-wavelength light (higher-energy photons) (Fox in Optical properties of solids. Oxford University Press Inc 2001 [1]). In a typical direct-gap semiconductor, electrons (solid circles) and holes (open circles) that are optically excited into conduction and valence bands, respectively, first relax to lower available energy levels by emitting multiple low-energy phonons and then relax to the ground state by recombination and emission of a photon (Fig. 77.1, ELaser and EPL are the excitation and emission photon energies, respectively). Since the photoexcited electron and hole are oppositely charged, they can attract each other through mutual Coulomb interaction and form a hydrogen-like electron–hole pair called an “exciton.”


Semiconductor Band gap Exciton Imaging Local conditions 


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© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  1. 1.Institute of Advanced EnergyKyoto UniversityUji, KyotoJapan

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