The first demonstration of laser cooling of solids was of an ytterbium doped fluorozirconate glass. While this
groundbreaking work successfully showed that it is possible to cool solids using laser cooling, rare-earth materials are
governed by Boltzmann statistics limiting their cooling ability to about 100 K. Direct-bandgap semiconductors, on the
other hand, are governed by Fermi-Dirac statistics, which allows for a theoretical cooling limit of 10 K as well as higher
cooling efficiencies. Recently, it was demonstrated that it is possible to cool CdS nanoribbons by 40 K. That success was
attributed to CdS strong electron-phonon coupling, which makes it possible to resonantly annihilate more than one
longitudinal optical phonon during each up conversion cycle. To further increase the cooling power, large external
quantum efficiency is required. A nanostructure is preferred because it creates confined excitons of tunable wavelength
and reduces the self-absorption of the anti-Stokes fluorescence owing to the shorter path length for photons to escape the
crystal. However, organically passivated quantum dots have a low quantum yield due to surface related trap states. A
core-shell nanostructure alleviates this problem by passivating the surface trap states and protecting against
environmental changes and photo-oxidative degradation. As such, we chose to investigate CdSe/ZnS core shell structure
for laser cooling applications. This article highlights the measurement of the anti-Stokes luminescence, the dependence
of the laser wavelength on the anti-Stokes emission of colloidal quantum dots, and the successful incorporation of
CdSe/ZnS into polymers.
The feasibility of a hydrogen implanted, direct band gap III-V semiconductors as new scintillators for fast neutron spectroscopy using the proton-recoil technique has been investigated. Direct band gap semiconductors have high radiative efficiency and have the potential of high photon yield per unit energy deposited, which are desirable features for a scintillator used for pulse height analysis. In this paper we present our computational results obtained using SRIM software for select materials. The expected depth profiles of implanted hydrogen ions have been applied to the n-p elastic recoil process in both InP and GaN. It is shown that, under ideal conditions, neutron irradiation of hydrogen implanted InP and GaN creates proton recoil scintillation with photon output being directly proportional to incoming neutron energy. It has been found that for the desirable dynamic range of neutron energies, loss to phonon creation in the lattice is negligible compared to energy used in electron excitation which results in the linear response in energy versus pulse height spectrum.