Stimulated emission due to the inelastic scattering from the heavy-hole exciton to the light-hole exciton in CuI thin films

Abstract

We have investigated high-excitation photoluminescence properties of CuI thin films with a thickness of 100 nm grown on a NaCl substrate by vacuum deposition. The energies of the heavy-hole and light-hole excitons in the CuI thin film are split at low temperatures by the thermal strain resulting from the difference in the thermal expansion coefficients of CuI and NaCl: the heavy-hole exciton is lower in energy than the light-hole exciton. Under resonant excitation of the heavy-hole exciton, a new photoluminescence band appears on the low-energy side of the heavy-hole exciton. The energy spacing between the new photoluminescence band and the heavy-hole exciton is almost equal to the splitting energy of the heavy-hole and light-hole excitons. The photoluminescence intensity exhibits an almost quadratic dependence on the excitation power. These results indicate that the new photoluminescence band originates from an inelastic scattering process from the heavy-hole-exciton state to the light-hole-exciton state. We have confirmed the existence of optical gain in the energy region of the new photoluminescence band by using a variable-stripe-length method. This fact demonstrates that the inelastic scattering process from the heavy-hole-exciton state to the light-hole-exciton state may lead to stimulated emission.

Optical properties of high-quality ZnO thin films grown by a sputtering method

“…At the lowest excitation power of 0.7 mJ/ cm 2 , the energy spacing between the P band and the free exciton is $60 meV, which is almost equal to the exciton binding energy [3]. Thus, we conclude that the P band originates from inelastic scattering of two n ¼ 1 excitons, the so-called P emission [9][10][11]. The energy of the P emission, _o P ; is given by [9] …”

Excitons in pristine silver iodide crystals

“…On further increasing excitation power from 0.8I 0 , the PL intensity at 2.936 eV has become superlinearly increased and narrowed in spectral shape. In general, a superlinearly-dependent exciton luminescence is explained by the stimulated emission due to the exciton-exciton collision process [10,11] or by the amplified spontaneous emission (so-called ASE), as reported for PbS films [12] and polymer film [13]. Since the observed lower-energy shift is too small to explain the result by such exciton-exciton collision process, both the observed superlinear dependence and the observed spectral narrowing may be assigned to the amplified spontaneous emission process.…”

Electrodeposition and optical properties of highly oriented γ-CuI thin films

“…These properties make ␥-CuI thin films very useful in dye sensitized solid state solar cell as a hole transporting and collecting agent [1,2] and potentially applicable in the fabrication of blue-emitting devices, field emission displays, and vacuum fluorescent displays [3][4][5]. CuI can also be used as a catalyst in organic synthesis [6,7] and application in the formation of both inorganic and biochemical supramolecular compounds [8,9].…”