There is a great interest in photonic substances with permittivity approaching zero, which are called the epsilon-nearzero (ENZ) materials. They have a potential for multiple applications in telecom industry. The newest ENZ materials based on transparent conductive oxides (TCOs) and transparent conductive nitrides (TCNs) still have limited spectral bands of the ENZ effect. We show with simulations based on the Effective Medium Theory that the limitation can be defeated by using nanocomposite films made of several TCOs/TCNs with the ENZ effect observed in different regions of optical spectrum that stand apart from each other. We proposed to make such composites with the concurrent multibeam multi-target pulsed laser deposition (CMBMT-PLD). The composite films of aluminum and gallium doped zinc oxide (AZO-GZO) at different proportions were made by concurrent PLD of AZO and GZO targets with two 532-nm laser beams from a frequency doubled Q-switched Nd:YAG laser in a 10-5-Torr vacuum. The deposition time varied from 10 to 50 min. The high-resolution scanning electron microscopy revealed that the films deposited on glass substrates were composed of nano-grains of the constituents with a size in the range 10-300 nm. Energy dispersive X-ray spectroscopy showed the presence of all the major constituents in the films. Optical absorption and reflection spectroscopy of the films in the visible and near-infrared regions demonstrated that they had a minimum of reflectance corresponding to the ENZ effect in a broad band (~ 200 nm) around 1200 nm in the agreement with theoretical predictions.
The objective of the paper was to demonstrate feasibility of a chemical (ammonia) sensor using dye-doped polymer nanocomposite with upconversion phosphor nano-particles. The micro-crystalline powder of upconversion rare-earth phosphor NaYF4:Yb3+, Er3+ was synthesized using a simple wet process followed up by baking in open air. The powder was reduced into nano-colloid with 100-nm nano-particles using the ball milling process. The nano-colloid was added to the solution of polymer poly(methyl methacrylate) known as PMMA. Additionally, a pH indicator dye (Phenol Red or Bromothymol Blue) was dissolved in polymer solution. The dye-doped polymer nanocomposite films were deposited on substrates using the dipping process followed by baking in order to evaporate the solvent. The deposited nano-photonic sensor film had bright green upconversion fluorescence with a spectral peak at 540 nm attributed to the nano-photonic rare-earth phosphor pumped with a 980 nm infrared diode laser. The spectrum of green emission matched the absorption band of the indicator dye exposed to ammonia. When the film was exposed to ammonia, it demonstrated an optical response in the form of the drop of intensity of green radiation measured with a silicon photodiode power meter. The sensitivity of the developed chemical sensor was close to 0.4% ammonia in air, and the response time was close to 5 minutes.
Nano-colloids and nano-crystals doped with ions of rare-earth elements have recently attracted a lot of attention in the scientific community due to their potential applications as biomarkers, fluorescent inks, gain media for lasers and optical amplifiers. Many rare-earth doped materials of different compositions, shapes and size distribution have been prepared by different synthetic methods, such as chemical vapor deposition, sol-gel process, micro-emulsion techniques, gas phase condensation methods, hydrothermal methods and laser ablation. In this paper micro-crystalline powder of the rare-earthdoped compound NaYF4:Yb3+, Er3+ was synthesized using a simple wet process followed by baking in open air. Under 980 nm diode laser excitation strong fluorescence in the 100 nm band around 1531-nm peak was observed from the synthesized micro-powder. The micro-powder was pulverized using a ball mill and prepared in the form of nano-colloids in different liquids. The particle size of the obtained nano-colloids was measured using an atomic force microscope and a dynamic light scatterometer. The size of the nano-particles was close to 100-nm. The nano-colloids were utilized as a filling media in capillary optical amplifiers and lasers. The gain of a 7-cm-long capillary optical amplifier (150-micron inner diameter) was as high as 6 dB at 200 mW pump power. The synthesized nano-colloids and the active optical components using them can be potentially used in optical communication, signal processing, optical computing, and other applications.
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