Size-Selective ZnO Nanocrystals as Spectral Energy Converters for Use in Advanced Display Devices.

In this paper, we report the synthesis of size-selective zinc oxide (ZnO) nanocrystals by three different techniques namely, auto-combustion, co-precipitation and atomizer and their effective energy conversion from harmful ultra-violet (UV, 365 nm) to visible green light. All the three methods are facile and convenient for the controlled synthesis of ZnO nanocrystals with an average crystallite size ranging 12-35 nm. The structural characterization using XRD revealed that the phase of ZnO nanocrystals was wurtzite. The morphology of the ZnO nanocrystals in all the three cases was found to be spherical and uniform as determined by High Resolution Transmission Electron Microscope. The novelty of the current work is to synthesize highly luminescent ultra-small ZnO nanocrystals without any dopant and their possible use as efficient spectral converters in displays. This result is further supported by steady-state photoluminescence spectra recorded under UV (365 nm) radiation as excitation. The presence of quantum confinement effect and increased surface to volume ratio perfectly established that ZnO nanocrystals synthesized by various routes have significant impact in the fields of optoelectronics, biomedical fields and advanced active display devices.

Self-Activated Green-Yellow Emitting Gd2CaZnO5 Phosphor for Efficient Ultra-Violet Light-Emitting Diodes.

A new self-activated green-yellow emitting Gd2CaZnO5 (GCZO) phosphor was synthesized using solid-state reaction method at high-temperature. XRD analysis confirmed the orthorhombic structure of the sample with the Pbnm space group. SEM micrographs reveal the irregular morphology with micron sized particles. Detailed photoluminescence (PL) analysis revealed that the excitation of the phosphor lies in the UV range (˜377 nm) with the related broad green-yellow emission centered at 530 nm. The broad band emission ranging from ˜450 nm to 650 nm can be attributed to the surface defects and oxygen vacancies. The calculated luminescence decay lifetime for the optimized phosphor was found to be 2.925 µs. Furthermore, the color-coordinate (x, y) were calculated and found to be (0.44, 0.45), which lies in the green-yellow (˜540 nm) region of the electromagnetic spectrum. The values of color coordinates and Color correlated temperature of 3289 K support the synthesized phosphor for the emission of warm white-light. These results perfectly established the suitability of this green-yellow emitting GCZO phosphor for Ultra-Violet Light-Emitting Diodes (LEDs) excited white-LED applications.

Unusual Red-Shift and Enhanced Photoluminescence of BaMgAl10O17:Eu2+ Phosphor Under Ultraviolet A Excitation for Modern Lighting Systems.

An unconventional red-shift but enhanced photoluminescence (PL) under ultraviolet A (UV-A) irradiation of Eu2+ doped Barium Magnesium Aluminate (BAM) phosphor prepared in both bulk and nanoforms useful for modern lighting applications has been presented. The solid-state reaction and solution combustion approaches were used for the preparation of phosphors with post-annealing step in reduced atmosphere. A significant broad blue-green (˜500 nm) PL associated with the transition of Eu2+ from 4f6 5d1 excited state to the 4f7 ground state has been observed. The observed shifts and PL intensities were found to be extremely reliant on the thermal processing parameters during the synthesis of phosphor/nanophosphormaterials. It's also important to note that the size of the phosphor particles have significant role in defining the red-shift of PL due to quantum confinement effect. Detailed structural and morphological characterizations were also done in this paper. The results are promising and suggest that the BAM phosphor is highly desirable for enhancing the brightness levels in modern lighting and display systems.