a ZnO is one of the most widely studied semiconductors due to its direct wide band gap and high exciton binding energy. Due to its ease of synthesis, robustness and low cost, ZnO has been applied in a wide range of devices, including nanogenerators, solar cells, and photodetectors. In this work, ZnO nanorods were synthesized in a single step using an aqueous method at temperatures below 100 1C. The nanorods were annealed in oxygen and nitrogen and a p-type polymer poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) was spray coated onto the top of ZnO nanorods to form a p-n junction. The I-V characteristics of the device showed that the annealing atmosphere had a significant effect on the rectification ratio of the device. Further analysis using Mott-Schottky, photoluminescence, and X-ray photoelectron spectroscopy (XPS) indicated that oxygen vacancy concentration correlated well with the free electron density in ZnO as well as the rectification ratio of the p-n junction devices. Devices made with ZnO nanorods annealed in nitrogen had a better rectification ratio than oxygen, representing a simple method to improve p-n junction diode behaviour through tuning the defect properties of the nanorods via controlled annealing.

Organic erbium complexes have long been of interest due to their potential for using the strong absorption into the organic to sensitise the erbium emission. Despite this interest there is remarkably little quantitative information on how effective the approach is and the discussion of the energy transfer mechanism is generally vague. Here we accurately quantify the sensitisation as a function of excitation pump density and model it using a rate equation approach. As a result, we can calculate the degree of population inversion for the erbium ions as a function of the pump intensity. We demonstrate that even when we increase the erbium concentration in the films from ~10 to ~80% we find a relatively small decrease in the sensitisation which we attribute to the large (>20 Å) Förster radius for the sensitisation process. We show that we can obtain population inversion in our films at very low pump powers ~600 mW/cm2. The calculated Förster radius for the organic erbium complexes suggests design rules for energy transfer between antennas and erbium ions in molecular systems and hybrid organic-inorganic nanoparticles.

Advanced 1.5-µm emitting materials that can be used to fabricate electrically driven light-emitting devices have the potential for developing cost-effective light sources for integrated silicon photonics. Sensitized erbium (Er 3+) in organic materials can give bright 1.5-µm luminescence and provide a route for realizing 1.5-µm organic light emitting diodes (OLEDs). However, the Er 3+ electroluminescence (EL) intensity needs to be further improved for device applications. Herein, an efficient 1.5-µm OLED made from a sensitized organic Er 3+ co-doped system is realized, where a "traditional" organic phosphorescent molecule with minimal triplet-triplet annihilation is used as a chromophore sensitizer. The chromophore provides efficient sensitization to a co-doped organic Er 3+ complex with a perfluorinatedligand shell. The large volume can protect the Er 3+ 1.5-µm luminescence from vibrational quenching. The average lifetime of the sensitized Er 3+ 1.5-µm luminescence reaches~0.86 ms, with a lifetime component of 2.65 ms, which is by far the longest Er 3+ lifetime in a hydrogen-abundant organic environment and can even compete with that obtained in the fully fluorinated organic Er 3+ system. The optimal sensitization enhances the Er 3+ luminescence by a factor of 1600 even with a high concentration of the phosphorescent molecule, and bright 1.5-µm OLEDs are obtained.

Photosensitisation of IR luminescence from an organic erbium complex is much greater with Zn(Cl-FBTZ)2 than with Zn(FBTZ)2.

Vibrational modes of chemical bonds in organic erbium (Er3+) materials play an important role in determining the efficiency of the 1.5 μm Er3+ emission. This work studies the energy coupling of the Er3+ intra-4f transitions and vibrational modes. The results demonstrate that the coupling introduces enormous nonradiative internal relaxation, which condenses the excited erbium population on to the 4I13/2 state. This suggests that vibrational modes can be advantageous for optimizing the branching ratio for the 1.5 μm transition in organic erbium materials. Through control of the quenching effect on to the 4I13/2 state and a reliable determination of intrinsic radiative rates, it is found that the pump power for population inversion can be reduced by an order of magnitude at high erbium concentrations compared to conventional inorganic erbium materials.