Four new metal iodates, namely, NaLn(IO) (Ln = La, Ce, Sm, and Eu), and a series of NaLa(IO):Ln (Ln = Sm and Eu) solid solutions were synthesized through hydrothermal reactions. The structures of the title compounds are similar to that of NaY(IO) crystallizing in the acentric monoclinic space group Cc. The iodate materials reveal layered structures composed of LnO square antiprisms and IO polyhedra, in which each layer is connected by the I···O interactions. NaLa(IO) suggests a great potential as a matrix for optical source attributed to its acentricity and broad transparency from visible to mid-IR region. The photoluminescence properties depending on the concentration of Sm reveal that NaLa(IO):Sm undergoes a self-quenching relaxation over 7 mol % of Sm by dipole-quadrupole interactions. Attributable to the asymmetric coordination environment of Ln, stronger electric dipole transitions compared to magnetic dipole transitions were observed for both compounds. In addition, the materials exhibit strong second-harmonic generation (SHG) responses and are type I phase-matchable. The structural origin of the SHG properties for the reported iodates is elucidated.

The luminous flux of the phosphor-converted white-light-emitting diode (WLED) is correlated to the optical properties of a phosphor, such as the excitation band, emission spectrum, and decay time. Also, the crystallinity, particle size, and morphology may influence the device performance, such as the luminous flux, as well as the device longevity and efficiency. The device application of the Ce 3+ -activated Y 3 Al 5 O 12 garnet phosphor was limited because of its strong patent. Its patent is set to expire in the year 2017, and the high-power operation of the WLED is becoming important. To obtain insights regarding its usability, Y 3 Al 5 O 12 :Ce 3+ phosphor was synthesized through flux-assisted solidstate reaction. It was found that this garnet phosphor has a very stable crystal structure and is inert in the processing environment. Its quantum yield reached 95%, and no photosaturation was shown within the measurement limit. It was also found that the synthetic procedures are very straightforward and that the particle size may be easily controlled. The luminous flux of the WLED was maximum when 17.7 µm D 50 was used. ARTICLE HISTORY

The luminescence behavior of certain phosphor material shows non-linearity within a specific photon excitation range, depending upon the activator and/or the host lattice. Conventionally, the absorption and emission characteristics of phosphors are measured using a spectrometer with a light source such as a xenon lamp. Herein, a new measurement system was set up to investigate luminescence saturation in inorganic phosphors. The effect of the environment on the longevity of the material has been examined for each attribute and the conditions for luminescence saturation have been discussed. © The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. Phosphor-converted white light-emitting diodes (pc-WLEDs) are widely used as a light source in liquid crystal displays and in solidstate lighting. They are known to be more stable than Ne-, fluorescent-, and halogen-lamps. In addition, they exhibit an excellent efficiency of ∼246 lm/W at 20 mA. The pc-WLEDs directly convert electrical energy into light. [1][2][3][4] In this conversion process, some electrical energy is dissipated in the form of heat, which leads to a decrease in the light efficiency. Heat sinks and cooling fans are also sources of LED power consumption that lead to a non-negligible decline in the lighting efficiency. 5,6 As the applications of high-power pc-WLEDs continue to increase, ensuring the reliability of these devices in terms of their optical characteristics and thermal stability has gained importance. In particular, a decrease in the efficiency of the power output and life-time has also been reported. 7,8 As the current density of the pc-WLEDs increases, their light output also increases and more heat is emitted. [9][10][11] It is known that the heat generated in the device increases the temperature of the active region of the quantum-well (QW) layer in the LED structure. The elevated temperature may also decrease the bandgap of the active region, which would cause the generation of more heat due to non-radiative recombination in the active region. This positive feedback process reduces the quantum efficiency of the LED and eventually causes degradation of its luminance and lifetime. 12 However, a more commonly encountered phenomenon is droop, in which the efficiency decreases over a certain level as the output increases. Although many studies have focused on clarifying the cause of the droop phenomenon and implicated sources such as carrier heating, carrier escape, and the Auger effect, the exact cause has not been identified as yet. [13][14][15][16] Therefore, further detailed studies are necessary. In general, the reliability of pc-WLE...

A Mn 4+ -doped germanate red-emitting phosphor, in which TiO 2 is partially substituted for GeO 2 , was synthesized by a solid-state reaction. The proportional composition of the compound was 3.5MgO-Ge 1-x Ti x O 2 -0.5MgF 2 :Mn 4+ . The main X-ray diffraction peak exhibited a gradual shift to lower angles depending on the synthesis temperature and the extent of Ti substitution. Substitution of GeO 2 with TiO 2 yielded a redshift of the broad excitation band (380-500 nm), which resulted from the 4 A 2 → 4 T 2 transition of Mn 4+ . Compared with the sample containing only GeO 2 , the relative luminescence of the sample in which GeO 2 was partially replaced with TiO 2 was increased by 19.3% for excitation at 450 nm.

We synthesized a single-phase Sr 2-x Eu x Si 5 N 8 phosphor using an ion transporter, Sr 3-x Eu x (PO 4 ) 2 , under atmospheric condition. This is a simple yet efficient synthetic route to the Sr 2-x Eu x Si 5 N 8 phosphor. The quantum efficiency of the phosphor is 90.7%, and the absorption ratio of the excitation wavelength at 450 nm is 88.3%, even though the inexpensive and commercially available raw materials are used without any pretreatment and are easy to handle in a normal atmosphere including oxygen and moisture. We believe that this approach can be used to prepare other nitride-based phosphors, whose synthesis is currently challenging.