Green single- and two-photon gap emission of thin-film CdS formed by infrared pulsed-laser deposition on glass

Thin-film CdS is formed by infrared pulsed-laser deposition (PLD) on glass. The film is excited with continuous-wave (CW) blue laser emission at 457.9 nm and with ultra-fast laser pulses of 200 fs at 801 nm. Both excitations cause green gap emission in the range from 2.43 to 2.45 eV at room temperature. Additionally, blue excitation evokes some sub-gap emission. The principle of detailed balance is used to describe the shape of the two-photon spectrum by modeling the absorption coefficient by the density of states and Urbach´s rule. Spectra measured through the glass substrate are shifted 40 meV to lower energies with respect to the emission emitted from the front side of the film. Using Beer´s law, it is shown that the shift is caused by stronger absorption at the glass/CdS interface. This is confirmed with the lack of geometry dependence of an interface-free 50-μm CdS platelet. The results show that two-photon spectroscopy is useful for revealing the interfacial absorption effects and PLD CdS exhibits outstanding emission properties, which are important for green light-emitting device fabrication