A review on the advancements in phosphor-converted light emitting diodes (pc-LEDs): Phosphor synthesis, device fabrication and characterization

In this work, an environmentally friendly and novel oxide-based mechanoluminescent material, Sr3Al2O6: Eu3+, which can serve as the alternative for the widely used but environmentally hazardous transition metal-doped sulfides is reported. This oxide could exhibit highly efficient photoluminescence, but even more efficient mechanoluminescence as embedded into polydimethylsiloxane matrix under mechanical stimulation. The emitting color of the resultant Sr3Al2O6: Eu3+/polydimethylsiloxane elastomer composites could be further manipulated by adjusting the synthesis atmosphere of the Sr3Al2O6: Eu3+ based on its unique self-reduction characteristic. Moreover, by combining the wavelength selectivity of photoluminescence and dynamic stress response of mechanoluminescence, Sr3Al2O6: Eu3+ enables the design of two types of intriguing devices. They are a dual-responsive anticounterfeiting flexible device activated by either photons or mechanics, and a comprehensive stretching/strain sensor capable of sensing both strain level and stretching states. In comparison to the conventional luminescent materials, with a rare combination of efficient photoluminescence, highly sensitive mechanoluminescence, and facile color tunability, Sr3Al2O6: Eu3+ is much more versatile and ideal for various advanced applications.

Efficient Mechanoluminescent Elastomers for Dual-Responsive Anticounterfeiting Device and Stretching/Strain Sensor with Multimode Sensibility

In the present paper, a comparative investigation on the structural and photoluminescence properties of Y2O3:Eu3+ phosphor prepared by different wet chemical synthesis routes such as sol-lyophilisation (SL), combustion (CR), hydrothermal (HT) and microwave assisted hydrothermal combustion (MHWC), has been reported for the first time. The MHWC derived phosphor exhibited better photoluminescence than that of the samples obtained with other adopted methods. Such outcomes were due to the increased crystallinity, well defined morphology and improved compositional homogeneity in the MWHC technique. The growth of the prepared phosphors was explained in the light of chemical kinetics. Jorgensen formula and nephelauxetic ratio was used to understand the ligand behavior of Eu–O bond and to estimate the electron phonon coupling in Y2O3:Eu3+ phosphor. The spectroscopic behavior of Y2O3:Eu3+ phosphor, prepared by different routes, was determined using Judd–Ofelt theory. Thermal stability, purity and efficiency of the emitted colour were checked on the basis of different synthetic approach. An efficient synthesis method for Y2O3:Eu3+ phosphor, compatible for industrial appliances, was proposed.

Synthesis of strong red emitting Y2O3:Eu3+ phosphor by potential chemical routes: comparative investigations on the structural evolutions, photometric properties and Judd–Ofelt analysis

A series of Dy3+/K+ doped calcium molybdate phosphors were synthesized by a hydrothermal synthesis method and structural, photoluminescence and decay studies were carried out. The crystal structure and phase of the prepared phosphors were investigated using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). These studies show that the phosphors are of a tetragonal structure with a nanorod morphology. The photoluminescence results indicate that these phosphors could be efficiently excited by near-ultraviolet radiation which causes emission in the blue and yellow regions. A novel approach was used to calculate different spectral parameters of powder samples using excitation spectra instead of conventional absorption spectra. Quantitative calculation of spectral parameters, luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting devices.

Excitation spectra and luminescence decay analysis of K+ compensated Dy3+ doped CaMoO4 phosphors

phosphor by potential chemical routes: comparative investigations on the structural evolutions, photometric properties and Judd-Ofelt analysis

This paper reports on the defect correlated self-quenching and spectroscopic investigation of calcium titanate (CaTiO3) phosphors. A series of CaTiO3 phosphors doped with trivalent europium (Eu3+) and codoped with potassium (K+) ions were prepared by the solid state reaction method. The X-ray diffraction results revealed that the obtained powder phosphors consisted out of a single-phase orthorhombic structure and it also indicated that the incorporation of the dopants/co-dopants did not affect the crystal structure. The scanning electron microscopy images revealed the irregular morphology of the prepared phosphors consisting out of μm sized diameter particles. The Eu3+ doped phosphors illuminated with ultraviolet light showed the characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+. As a charge compensator, K+ ions were incorporated into the CaTiO3:Eu3+ phosphors, which enhanced the photoluminescence (PL) intensities depending on the doping concentration of K+. The concentration quenching of Eu3+ in this host is discussed in the light of ion-ion interaction, electron phonon coupling, and defect to ion energy transfer. The spectral characteristics and the Eu-O ligand behaviour were determined using the Judd-Ofelt theory from the PL spectra instead of the absorption spectra. The CIE (International Commission on Illumination) parameters were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicated the suitability of K+ compensated the CaTiO3:Eu3+ phosphor for pure red emission in light-emitting diode applications.

Defect correlated fluorescent quenching and electron phonon coupling in the spectral transition of Eu3+ in CaTiO3 for red emission in display application

This paper reports the structural, optical and luminescence properties of Yb3+/Er3+ codoped Y2O3 phosphor synthesized by combustion method. The prepared phosphor was characterized by X-ray diffraction (XRD). XRD studies confirm the body-centered cubic structure of the phosphor. The optical properties such as diffuse reflectance (DR), photoluminescence and thermoluminescence were studied. DR spectra were used to determine the bandgap of the phosphor. Mechanism of upconversion by two-photon and energy transfer processes are interpreted and explained. The color coordinates were measured and the color tunability was analyzed as a function of the 980 nm excitation source power. Different trapping parameters associated with the glow peak were calculated by various glow curve methods.

M. Chowdhury

Papers

Defect correlated fluorescent quenching and electron phonon coupling in the spectral transition of Eu3+ in CaTiO3 for red emission in display application

Band gap and trapping parameters of color tunable Yb3+/Er3+ codoped Y2O3 upconversion phosphor synthesized by combustion route

A comparative investigation on ion impact parameters and TL response of Y2O3:Tb3+ nanophosphor exposed to swift heavy ions for space dosimetry

Kinetic parameters of γ-irradiated Y2O3 phosphors: Effect of doping/codoping and heating rate