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Quantum-dot (QD) technology has become a very transversal technology finding application in an increasing number of scientific and industrial fields. At the forefront of this development is the well-studied InAs/GaAs QD system. However, the limitations imposed by the fixed InAs-GaAs band offsets and by the difficulties to control the QD morphology due to the capping process still difficult the precise control of QD band structure that would allow the required design in different applications. The use of a certain capping layer (CL) material different than GaAs has been particularly employed to tune the ground state energy of InAs/GaAs QDs through strain and band structure engineering, so achieving the longwavelength telecommunication windows as one of the most pursued targets. This work is mainly focused on the achievement of a higher tunability of the properties of InAs/GaAs QDs by the application of thin GaAs(Sb)(N) CLs and the optimization of the capping process in order to improve their suitability to any optoelectronic device, and more in particular to laser diodes and solar cells. GaAs(Sb)(N)/InAs/GaAs QDs are a highly versatile system in which the use of Sb and N allows for the tunability of the QD ground state while providing a huge degree of freedom regarding the QD-CL band-alignment, according to the requirements of the field of application. quieren, por lo tanto, enfoques alternativos con el fin de mejorar la eficiencia de conversión. En particular, se demuestra que parámetros como la profundidad del pozo de potencial en el CL, su espesor, y su estructura, así como el alineamiento de bandas resultante, juegan un papel importante en la extracción y el transporte de portadores en células solares de QD.

A new Eu -substituted CsK Y[VO ] glaserite-type orthovanadate phosphor was synthesized by the conventional high temperature solid-state reaction method. The phase purity was confirmed by powder X-ray diffraction study and it reveals that all the compositions crystallize in the hexagonal structure. The morphology and elemental composition were measured by FE-SEM with Energy Dispersive Analysis Of X Rays (EDAX). The band gap is determined by diffuse reflectance spectra. The self-activated luminescence of the host and Eu -substituted luminescence behaviours were studied in detail by photoluminescence spectra. The host CsK Y[VO ] shows green emission, whereas the Eu -substituted compositions show red emission. Effect of Eu concentrations on the photoluminescence behaviour were also been studied. The Eu -doped samples show not only several sharp emission lines but also a broad emission band due to presence of the [VO ] in the host, which clearly indicates that there is incomplete energy transfer from (VO ) charge transfer band to Eu The life time of the phosphors also been studied. The Commission Internationale de l'Eclairage (CIE) chromaticity colour coordinates were calculated and it is very much closer to the National Television Standard Committee (NTSC) standards. These investigations evidently reveal that the self-activated and Eu -activated phosphors show a great potential applications as a red phosphor for solid-state lighting includes white light-emitting diodes (wLEDs).

A series of NaBaBi(2-x)(PO4)3:xDy3+ eulytite type phosphors with varying doping concentrations were synthesized using a conventional solid-state reaction. The crystalline nature and phase formation of the phosphor were confirmed by the PXRD technique. FESEM was used to examine the surface morphology. UV-DRS measurements were used to quantify the band gap of the host and Dy3+ ion doped phosphors. The phosphors’ photoluminescence properties were thoroughly investigated. According to the excitation spectra, these phosphors show a strong absorption band in the near-ultraviolet (NUV) region, extending from 250 to 450 nm. Under the excitation of 352 nm, the peaks of the emission spectra of Dy3+ ions are located at 485 nm (blue), 575 nm (yellow) and 666 nm (red), corresponding to the magnetic dipole 4F9/2→6H15/2 transition, the electric dipole 4F9/2→6H13/2 transition and the 4F9/2→6H11/2 transition. The optimal concentration of Dy3+ doped phosphor is x = 0.075 and the major concentration quenching mechanism is accomplished by energy transfer between the nearest-neighbour ions. The critical transfer distance (Rc) is estimated to be about 19.01. The Commission International deI’Eclairage (CIE) of NaBaBi1.925(PO4)3:0.075Dy3+ phosphor was calculated to be (x = 0.341 and y = 0.374), which was very close to the “ideal white” (x = 0.33, y = 0.33). Present findings suggest that the phosphor might be a viable option for producing a white-light-emitting phosphor under NUV activation.