Recent advances in two-dimensional perovskite materials for light-emitting diodes.

Light-emitting diodes (LEDs) are an indispensable part of our daily life. After being studied for a few decades, this field still has some room for improvement. In this regard, perovskite materials may take the leading role. In recent years, LEDs have become a most explored topic, owing to their various applications in photodetectors, solar cells, lasers, and so on. Noticeably, they exhibit significant characteristics in developing LEDs. The luminous efficiency of LEDs can be significantly enhanced by the combination of a poor illumination LED with low-dimensional perovskite. In 2014, the first perovskite-based LED was illuminated at room temperature. Furthermore, two-dimensional (2D) perovskites have enriched this field because of their optical and electronic properties and comparatively high stability in ambient conditions. Recent and relevant advancements in LEDs using low-dimensional perovskites including zero-dimensional to three-dimensional materials is reported. The major focus of this article is based on the 2D perovskites and their heterostructures (i.e., a combination of 2D perovskites with transition metal dichalcogenides, graphene, and hexagonal boron nitride). In comparison to 2D perovskites, heterostructures exhibit more potential for application in LEDs. State-of-the-art perovskite-based LEDs, current challenges, and prospects are also discussed.

The Role of Anions in Rare-earth Activated Inorganic Host Materials for its Luminescence Characteristics.

This work is inspired from the comprehensive work done by our research team aimed at improving the efficiency of white light emitting diodes (LEDs) through improvements in the colour rendering index of the red light (CRI), one of the primary colours of white light. Such work is triggered through the incorporation of anions (BO33-, PO43-, SO42-), either individually or as an integral part of dopant activated inorganic phosphor host materials. Numerous host materials such as ZnO, Y2O3, Ca3(PO4)2, CaMoO4, ABPO4, ABSO4 (where A represents alkali metals and B alkaline earth metals) have been considered ideal hosts materials for studying luminescence properties of materials (including other phosphors). In addition, red emitting dopants such as Sm3+, Eu3+ and Ce3+ have been incorporated into these host materials to achieve a higher CRI of red colour, an essential component of white light. The role anions in various materials is multifaceted; firstly, it acts as sensitizer whereby it absorbs excitation energy and transfers it non-radiatively to the dopants, secondly, it acts as a charge compensator to dopants with a charge of + 3, thirdly, it creates crystal fields that affects the electronic transitions of the dopants and fourthly, it creates a stable crystal structure that allows for dopant embedding. By understanding the exact role of these anions and their interactions with the host lattice and dopant ions, we could further optimize the luminescent properties of these activated host materials, which leads to higher efficiencies and performances in white light-emitting diodes and other lighting technologies. This work is a comprehensive review of the work undertaken by our research team aimed at enhancing the luminescent properties of WLEDs.

A Review of the Efficiency of White Light (or Other) Emissions in Singly and Co-Doped Dy3+ Ions in Different Host (Phosphate, Silicate, Aluminate) Materials.

In this review we will present several research papers pertaining to white colour (or other) emission from Dy3+ doped and undoped phosphor materials. The search for a single component phosphor material that could deliver high quality white light under UV or near UV excitation is an area of active research for commercial purposes. Amongst all rare earth elements Dy3+ is the only ion that could deliver simultaneously blue and yellow light under UV excitation. In optimizing the Yellow/Blue emission intensity ratios, white light emission can be realized. Dy3+ (4f9) displays approximately 4 emission peaks at around 480 nm, 575 nm, 670 and 758 nm corresponding to transitions from the metastable 4F9/2 state to various lower states, such as 6H15/2 (blue), 6H13/2 (yellow), 6H11/2 (red) and 6H9/2 (brownish red), respectively. In general, the hypersensitive transition at 6H13/2 (yellow) is electric dipole in nature and becomes prominent only when Dy3+ ions are positioned at low symmetric sites with no inversion symmetry in the host matrix. On the other hand, the blue magnetic dipole transition at 6H15/2 becomes prominent only when Dy3+ ions are positioned at highly symmetric sites in the host material with inversion symmetry. Despite the white colour emission from the Dy3+ ions, these transitions are mainly associated with parity forbidden 4f -4f transitions, the white light produced maybe diminished at times, hence the need to include a sensitizer to bolster the forbidden transitions experienced by Dy3+ ions. In this review we will focus on the variability of the Yellow/Blue emission intensities in different host materials (phosphates, silicates, and aluminates) from Dy3+ ions (doped or undoped) by studying their photoluminescent properties (PL), their CIE chromaticity coordinates and correlated colour temperature (CCT) values for white colour emissions that is adaptable to different environmental conditions.