Luminescence Saturation in Inorganic Phosphors under High Flux of Photon Excitation

Abstract

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...

Challenges and Strategies to Design Phosphors for Future White Light Emitting Diodes

“…Figure 5a shows photoluminescence spectra of YAG:Ce 3+ at different input powers of the 450 nm laser diode in pulse mode. 57 At lower input powers, the photoluminescence intensity of the phosphor increases almost linearly with the increasing input power. However, at an input current above 550 mA, the photoluminescence efficiency of the phosphor starts decreasing.…”

“…Such laser diodes with a high intensity of blue-light emission without any efficiency droop are used to study the fate of phosphors at a high-power input intensity. Figure a shows photoluminescence spectra of YAG:Ce 3+ at different input powers of the 450 nm laser diode in pulse mode . At lower input powers, the photoluminescence intensity of the phosphor increases almost linearly with the increasing input power.…”

“…(a) Photoluminescence spectra of YAG:Ce 3+ with increasing input power laser diode pulsed excitation at 450 nm with a frequency of 3.57 Hz. Reprinted with permission from ref . Copyright 2018 Institute of Physics.…”