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 ⁴F_9/2 state to various lower states, such as ⁶H_15/2 (blue), ⁶H_13/2 (yellow), ⁶H_11/2 (red) and ⁶H_9/2 (brownish red), respectively. In general, the hypersensitive transition at ⁶H_13/2 (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 ⁶H_15/2 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.