Low visible light absorption and high charge carrier recombination rate are two main disadvantages of TiO2 as a photocatalyst which severely limit its practical applications. To overcome the problems, Fe mono-doped and (Fe+Mo) co-doped TiO2 were synthesized and studied. It was found that (Fe+Mo) co-doping can further increase the visible absorption and improve the photocatalytic property of TiO2 compared with Fe mono-doping; Fe mono-doping improves the photocatalytic property of TiO2 only at very low doping level (Fe concentration less than 1.0%), while by co-doping a small amount of Mo with Fe, the effective doping concentration of Fe can be pushed to a higher level and the photocatalytic property of TiO2 can be further improved. Photoluminescence spectra indicated that Mo dopant may play a role in retarding the recombination process when co-doped into TiO2 with Fe. The mechanism behind was discussed. It was suggested that doping a small amount of Mo into Fe-TiO2 might be an efficient way to further improve the photocatalytic property of Fe-TiO2 without losing its photocatalytic specificity.

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Current crowding effects (CCEs) on light extraction efficiency (LEE) of conventional GaN-based light-emitting diodes (LEDs) are analyzed through Monte Carlo ray-tracing simulation. The non-uniform radiative power distribution of the active layer of the Monte Carlo model is obtained based on the current spreading theory and rate equation. The simulation results illustrate that CCE around n-pad (n-CCE) has little effect on LEE, while CCE around p-pad (p-CCE) results in a notable LEE droop due to the significant absorption of photons emitted under p-pad. LEE droop is alleviated by a SiO₂ current blocking layer (CBL) and reflective p-pad. Compared to the conventional LEDs without CBL, the simulated LEE of LEDs with CBL at 20 A/cm² and 70 A/cm² is enhanced by 7.7% and 19.0%, respectively. It is further enhanced by 7.6% and 11.4% after employing a reflective p-pad due to decreased absorption. These enhancements are in accordance with the experimental results. Output power of LEDs with CBL is enhanced by 8.7% and 18.2% at 20 A/cm² and 70 A/cm², respectively. And the reflective p-pad results in a further enhancement of 8.9% and 12.7%.

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