We report the temperature dependence of Er optical centers in GaN epilayers prepared by metal-organic chemical vapor deposition under the resonant excitation (4 I 15/2 → 4 I 9/2) excitation using a Ti:Sapphire laser (λexc = 809 nm). High resolution infrared spectroscopy and temperature dependence measurements of photoluminescence intensity from Er ions in GaN have been performed to identify the crystal filed splitting of the first excited state, 4 I 13/2. Here, we have employed a simple approach to determine activation energies which are related to the thermal population of electrons from the lowest level to the higher level of the crystal field splitting of the first excited state.

The Eu3+ doped CaIn2O4 is a novel oxide phosphor useful for multifunctional applications such as display systems, lasers, energy-converters, photocatalysts, optical imaging, medical tools, and several others. Here, a natural aloe-vera gel is explored to obtain a precursor gel bridging Eu3+, Ca2+ and In3+ cations in a network so that it yields Eu3+:CaIn2O4 of small crystallites bonding over a grafted C-sp2 surface layer. The Eu3+ in varied from 0.1 to 2 mol% promptly promotes blue and red light-emissions in two major bands over 300-580 nm and 600-900 nm in 5DJ → 7FJ′ (J = 3, 2, 1 and J′ = 4 →1) and 5D0 → 7F1→ 4 transitions in the Eu3+ species, what is it is required in many optical and catalytic devices. The novel results are described in correlation to the light absorption and core-shell nanostructure.

In this work, calcium fluoride (CaF2) and Tb3+-doped calcium fluoride (CaF2:Tb3+) thin films were prepared by electrochemical methods. According to EDS and XRD results, CaF2 thin films undergo through a phase transformation from cubic CaF2:Tb3+ to NaTbF4 when Tb3+ concentration in the electrolytic bath is increased. So that, peaks showed a very clear shifting towards lower angles. On the other hand, optical absorption results showed the typical range of transparency from IR to UV, and from photoluminescence (PL) spectra results it can be observed that it is possible to identify the f-f transition of Tb3+. The PL at low temperature allows finding the quenching concentration when the PL intensity decreases at the highest doping concentration value. However, the results also showed that the transition of Tb3+ does not seem to be affected by the coexistence of the secondary phases such as cubic NaTbF4. In the case of RE-doped CaF2 thin films materials, they can be used with a double purpose for solar cell applications, not only as antireflecting coating, but also as a host for lanthanide doping for down conversion of light. These properties could be very useful for photovoltaic applications, so that the spectral range of light conversion could be increased to achieve higher conversion efficiency values.

Optical transmission spectra are collected in the ferromagnetic state of GdN at various temperatures. The temperature dependent extinction coefficient extracted from the transmission measurements show that the conduction and valence band states are spin polarized. The results confirm the LSDA+U estimates of the energy gap associated with the majority/minority-spins and also the magnitude of the spin splitting.

A modification of the growth structure of Eu-doped GaN (GaN:Eu) from a monolayer to a multilayer structure (MLS) consisting of alternating GaN and GaN:Eu, was shown to enhance the emission properties. Similarly, lowering the growth temperature of the GaN:Eu to 960°C nearly doubled the photoluminescence emission intensity, and also enhanced device performance. Hence, to design a higher power GaN:Eu red LED, a multilayer structure consisting of 40 pairs of alternating GaN and GaN:Eu was grown at 960°C. This combination resulted in the fabrication of an LED with a maximum output power of 110 μW, which is 5.8 times more output power per GaN:Eu layer thickness as compared to the best previously reported device. Moreover, it was found that the MLS sample grown at 960°C maintained a high crystal quality with low surface roughness, which enabled an increase in the number of pairs from 40 pairs to 100 pairs. An MLS-LED consisting of 100 pairs of alternating GaN/GaN:Eu layers was successfully fabricated, and had a maximum output power of 375 μW with an external quantum efficiency of 4.6%. These are the highest values reported for this system.

We report on the structural and electrical properties of epitaxial SmN thin films grown by molecular beam epitaxy. The effect of the growth temperature and nitrogen precursor, either pure molecular N2 or NH3 was investigated. The structural quality of SmN was assessed by X-ray diffraction and the epitaxial growth character is observed over the entire range of growth temperatures, from 300°C to 800°C, with both nitrogen precursors. The highest quality films are produced at a growth temperature of about 430°C by using N2 as a nitrogen precursor. Hall Effect and resistivity measurements establish that SmN films are heavily n-type doped semiconductors, suggesting the presence of nitrogen vacancies, a recurring phenomenon in rare earth nitride compounds.

Periodic array of metallic nanocylinder combined with the highly luminous dielectric layer is a good platform to control the intensity, spectral shape and directionality of photoluminescence (PL). In spite of its importance, the effect of cylinder height on the PL properties has not been verified experimentally. Here we investigate the effect of cylinder height on the PL properties both experimentally and numerically. The system consisted of a highly luminous layer made of Eu(III) complex and a series of periodic array of aluminum nanocylinders with different heights. The strongest directional PL was achieved when the height is similar to the diameter, i.e., the aspect ratio close to unity. Our finding is useful for designing the compact and efficient luminescence source with directional output.

In0.06Ga0.94N/GaN superlattices (SLs) grown on sapphire (0001) by metalorganic chemical vapor deposition were studied before and after europium (Eu) ion implantation to understand the strain induced-effects in the SL structure. The implanted SLs were investigated as a function of the thermal annealing temperature up to 1000 °C in nitrogen ambient. Temperature dependent photoluminescence spectra showed a red-shift of the SL emission peaks due the quantum confined Stark effect, followed by a blue-shift due to In atoms out-diffusion from the In0.06Ga0.94N quantum well, for both Eu ions implanted and unimplanted SLs. The amplitude of observed spectral shifts was smaller and the line width of the SLs emission peaks were narrower in the SLs:Eu3+ as compared to the unimplanted SLs. It is concluded that Eu3+ ions modified the strain in the SLs acting like impurity and/or defects getter in implantation degraded SLs resulting in material phase purification and improvements of SLs optical properties.

GdN/SmN based superlattices have been grown by molecular beam epitaxy. In-situ reflection high energy electron diffraction was used to evaluate the evolution of the epitaxial growth and the structural properties were assessed by ex-situ X-ray diffraction. Hall Effect and resistivity measurements as a function of the temperature establish that the superlattices are heavily n-type doped semiconductors and the electrical conduction resides in both REN layers, SmN and GdN.