Photoluminescence of Alq3‐ and Tb‐activated aluminium–tris(8‐hydroxyquinoline) complex for blue chip‐excited OLEDs

The tris(8‐hydroxyquinoline)–aluminium complex is the most important and widely studied as electron transporting and green light emitting material. Alq₃ and Tb_xAl_(1‐x)q₃ have been synthesized (where x = 0.1, 0.3, 0.5, 0.7 and 0.9) and blended films of Alq₃ and Tb_xAl_(1‐x)q₃ with PMMA and PS at different percentage weight (wt%) concentrations (e.g., 0.1, 1, 5, 10, 25 and 50 wt%) have been prepared. The synthesized materials and their blended thin films have been characterized by a photoluminescence (PL) technique; the synthesis and PL characterization are reported in this paper. The synthesized metal complex shows bright emission of green light with blue light excitation (440 nm) and the prepared Tb_xAl_(1‐x)q₃ phosphor may be applicable in blue chip‐excited OLEDs for the newly developed wallpaper lighting technology. Copyright © 2012 John Wiley & Sons, Ltd.     

Intense photon emission induced by fracture of γ–irradiated Dy‐, Tm‐, Sm‐ and Mn‐doped CaSO4 single crystals

When an γ‐irradiated Dy‐, Tm‐, Sm‐ or Mn‐doped CaSO₄ crystal is impulsively deformed, two peaks appear in the ML intensity versus time curve, whereby the first ML peak is found in the deformation region and the second in the post‐deformation region of the crystals. In this study, intensities I_m1 and I_m2 corresponding to first and second ML peaks, respectively, increased linearly with an impact velocity v₀ of the piston used to deform the crystals, and times t_m1 and t_m2 corresponding to the first and second ML peaks, respectively, decreased with impact velocity. Total ML intensity initially increased with impact velocity and then reached a saturation value for higher values of impact velocity. ML intensity increased with increasing γ‐doses and size of crystals. Results showed that the electric field produced as a result of charging of newly‐created surfaces caused tunneling of electrons to the valence band of the hole‐trapping centres. The free holes generated moved in the valence band and their subsequent recombination with electron trapping centres released energy, thereby resulting in excitation of luminescent centres. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence characteristics of (Y,Gd)BO3:RE (RE = Eu3+, Ce3+, Dy3+ and Tb3+) phosphors for blue chip and near‐UV white LEDs

A series of Eu³⁺‐, Ce³⁺‐, Dy³⁺‐ and Tb³⁺‐doped (Y,Gd)BO₃ phosphors was synthesized by a solid‐state diffusion method. X‐Ray diffraction confirmed their hexagonal structure and the scanning electron microscopy results showed crystalline particles. The excitation spectra revealed that (Y,Gd)BO₃ phosphors doped with Eu³⁺, Ce³⁺ , Dy³⁺ and Tb³⁺ are effectively excited with near UV‐light of 395 nm/blue light, 364, 351 and 314 nm, respectively. Photoluminescence spectra of Eu³⁺‐, Ce³⁺‐ and Tb³⁺/Dy³⁺‐doped phosphor showed intense emission of reddish orange, blue and white light, respectively. The phosphor Y_0.60Gd_0.38BO₃:Ce_0.02 showed CIE 1931 color coordinates of (0.158, 0.031) and better color purity compared with commercially available blue BAM:Eu²⁺ phosphor. The phosphor (Y,Gd)BO₃ doped with Eu³⁺, Dy³⁺ and Tb³⁺ showed CIE 1931 color coordinates of (0.667, 0.332), (0.251, 0.299) and (0.333, 0.391) respectively. Significant photoluminescence characteristics of the prepared phosphors indicate that they might serve as potential candidates for blue chip and near‐UV white light‐emitting diode applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Versatility of thermoluminescence materials and radiation dosimetry – A review

Thermoluminescence (TL) materials exhibit a wide range of applications in different areas such as personal dosimetry, environmental dosimetry, medical research etc. Doping of different rare earth impurities in different hosts is responsible for changing the properties of materials useful for various applications in different fields. These materials can be irradiated by different types of beams such as γ‐rays, X‐rays, electrons, neutrons etc. Various radiation regimes, as well as their dose–response range, play an important role in thermoluminescence dosimetry. Several TL materials, such as glass, microcrystalline, nanostructured inorganic materials and recently developed materials, are reviewed and described in this article.     

Persistent phosphors for luminous paints: A review

The article briefly reports the fundamental scientific principles and landmarks in the field of luminescence and further enlightens the importance of persistent phosphor that is now widely used in luminous paints. Its main focus is on phosphorescence that makes use of lanthanides that have gained paramount importance in various cross-sections of luminescent applications. Both inorganic and organic afterglow materials, synthesis and characterization along with skilled researchers' essential updates on emerging trends and efforts are elucidated at length. It exclusively reviews the red/green/blue organic/inorganic/hybrid phosphorescent materials and the latest advances in the development of novel long afterglow materials that can accelerate the green technology in the world of luminescence.     

Solid‐state synthesis and luminescent properties of yellow‐emitting phosphor NaY(MoO4)2:Dy3+ for white light‐emitting diodes

A yellow‐emitting phosphor NaY(MoO₄)₂:Dy³⁺ was synthesized using a solid‐state reaction at 550 °C for 4 h, and its luminescent properties were investigated. Its phase formation was studied using X‐ray powder diffraction analysis, and there were no crystalline phases other than NaY(MoO₄)₂. NaY(MoO₄)₂:Dy³⁺ produced yellow emission under 386 or 453 nm excitation, and the prominent luminescence was yellow (575 nm) due to the ⁴ F_9/2→⁶H_13/2 transition of Dy³⁺. For the 575 nm emission, the excitation spectrum had one broad band and some narrow peaks; the peaks were located at 290, 351, 365, 386, 426, 453 and 474 nm. Emission intensities were influenced by the Dy³⁺ doping content and a concentration quenching effect was observed; the phenomenon was also proved by the decay curves. Moreover, the Commission International de I'Eclairage chromaticity coordinates of NaY(MoO₄)₂:Dy³⁺ showed similar values at different Dy³⁺ concentrations, and were located in the yellow region. Copyright © 2015 John Wiley & Sons, Ltd.     

Dy3+‐activated NaM4 (VO4)3 (M = Ca,Ba, Sr) phosphor for near‐UV solid‐state lighting

We report the photoluminescence characterization of Dy³⁺‐activated NaM₄(VO₄)₃ (M = Ca, Ba, Sr) phosphors prepared by a solid‐state method. The synthesis was confirmed by X‐ray diffraction (XRD) characterization and photoluminescence (PL) emission results showed sharp blue and yellow bands for NaM₄(VO₄)₃ (M = Ca, Ba, Sr):Dy³⁺ phosphors at the excitation wavelength of 323 nm, which is near‐UV excitation. Thus, these phosphors could be applicable for near‐UV excited solid‐state lighting devices. Copyright © 2011 John Wiley & Sons, Ltd.     

Wet‐chemical preparation of Ce3+‐activated K2LaX5 (X = Cl,Br or I) phosphors

There has been a renewed interest in Ce³⁺‐activated halide phosphors due to applications as scintillation detectors, especially for positron emission tomography. For K₂LaCl₅, the light yield increases and the energy resolution (FWHM) improves with increasing Ce³⁺ doping. K₂LaX₅ compounds are also important as laser hosts for the mid‐IR range. K₂LaCl₅:Nd crystals show bright mid‐IR luminescence, which makes them a candidate for IR laser materials. Efficient emission in the IR range has also been reported in K₂LaCl₅:U³⁺. A one‐step, wet chemical process for preparing Ce³⁺‐activated K₂LaCl₅ phosphor is described. Intense luminescence of Ce³⁺ can be observed in the as‐prepared powders without any heat treatment. The availability of such powders opens up several exciting possibilities, such as growing single crystals without going to the high temperatures required for melting the constituent chlorides, or even obtaining processed, transparent, Ce³⁺‐activated materials without taking recourse to crystal growth. Copyright © 2011 John Wiley & Sons, Ltd.     

Photoluminescence in rare earth‐doped complex hexafluoride phosphors

In this study, using a simple combustion process and a wet chemical process, fluorides showing intense photoluminescence were prepared and developed as low‐cost phosphors. The prepared phosphors were characterized by photoluminescence (PL) techniques. PL emission spectra of the phosphor suggest the presence of Eu³⁺ as well as Eu²⁺ ions in LiMgBF₆:Eu and Li₂NaBF₆:Eu lattice sites. This article summarizes the fundamentals and possible applications of optically useful inorganic fluoride with visible photoluminescence of doped Eu³⁺ and Eu²⁺ ions. Our results on LiMgBF₆:Ce and Li₂NaBF₆:Ce are also reported. Copyright © 2011 John Wiley & Sons, Ltd.     

The long rod-shaped Sr2MgSi2O7:Eu2+,Dy3+ with ultrahigh afterglow performance

The afterglow properties of long afterglow luminescent materials are greatly affected by their defects, which are distributed on the grain surface. Increasing the exposed surface area is an important method to improve the afterglow performance. In this research, long rod-shaped long afterglow materials Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were prepared using the hydrothermal-coprecipitation method. When the reaction time reached 96 h, the length of the afterglow materials could grow to 2 mm, and the sintering temperature was just 1150°C. The emission spectra of all obtained samples upon excitation at 397 nm had a maximum of 465 nm, which belonged to the representative transition of Eu²⁺. The initial brightness was 1.35 cd/m². The afterglow time could reach 19 h, giving a good afterglow performance. The research on this kind of material has essential significance in the exploration of luminescence mechanisms and their applications.