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The high phonon energy and short infrared cut-off wavelength of conventional oxide glass (or crystal) hosts are the limitations to achieve mid-infrared (MIR, λ≥2.5μm) luminescence. In present study, the luminescence performance of low phonon and non-conventional TeO2-TiO2-La2O3-based glass (TTL) host doped with Ho3+ and Ho3+/Yb3+ has been investigated, for visible to MIR range. The MIR emission band with peak at 2.88μm (Ho3+:5I6→5I7) and NIR band at 2.04μm (Ho3+:5I7→5I8) has been realized from Ho3+ singly doped TTL glass due to low phonon energy and extended transmission window of the host. Intensity of MIR and NIR emission bands have enhanced significantly in Ho3+/Yb3+: TTL glass under Yb3+ excitation, signifying an efficient Yb3+→Ho3+ energy transfer. The Judd-Ofelt analysis, on Ho3+ absorption characteristics reveals relatively better radiative transition probability (34.4s−1) and branching ratio (10.5%), which is associated to Ho3+:5I6→5I7 transition. The effective bandwidth of 2.88μm emission band is 180nm, with stimulated emission cross-section is 4.26×10-21cm2 and its gain bandwidth has been evaluated as 7.67×10-26cm3. For 2.04μm (Ho3+:5I7→5I8) emission band, the effective bandwidth of 160.5nm and gain bandwidth of 7.26×10-26cm3 have been accomplished. The non-resonant Förster-Dexter method has been applied to Ho3+/Yb3+: TTL glass on emission (donor, Yb3+) and absorption (acceptor, Ho3+) cross sections. The evaluated donor-donor (CDD) and donor-acceptor (CDA) energy transfer micro-parameters are 1.02×10-38 and 5.88×10-41cm6/s respectively while, maximum energy transfer efficiency has been 80%. In concise, Ho3+/Yb3+ codoped TeO2–TiO2–La2O3 glass host has revealed its potential for MIR to NIR photonic applications. [ABSTRACT FROM AUTHOR]

A detailed analysis of the radiative recombination processes in Ag(InGa)Se2 thin films grown by a three-stage method was carried out by photoluminescence. The temperature and excitation dependence of the photoluminescence spectra was used to identify the recombination types and determine the ionization energy of the defects in the films. Significant differences were observed between the spectra of the Ag-rich and Ag-poor samples. The Ag-rich films were dominated by two emission peaks of donor acceptor pairs (DAPs). The DAP at lower energy level is attributed to recombination of donor level 13.8 meV (Agi) with acceptor level 70.3 meV (AgIn), while the one at high energy level is assigned to recombination of donor level 18.5 meV (Agi) with acceptor level 108.9 (Ag

Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals. [ABSTRACT FROM AUTHOR]

We exploit inter-layer radiative transitions to provide gains to amplify terahertz waves in graphene heterostructures. This is achieved by properly doping graphene sheets and aligning their energy bands so that the processes of stimulated emissions can overwhelm absorptions. We derive an expression for the gain estimation and show the gain is insensitive to temperature variation. Moreover, the gain is broadband and can be strong enough to compensate the free carrier loss, indicating graphene based room temperature terahertz lasers are feasible. [ABSTRACT FROM AUTHOR]