Abstract
In everyday life, we are continually exposed to different lighting systems, from the home interior to car lights and from public lighting to displays. The basic emission principles on which they are based range from the old incandescent lamps to the well-established compact fluorescent lamps (CFL) and to the more modern Light Emitting Diode (LEDs) that are dominating the actual market and also promise greater development in the coming years. In the LED technology, the key point is the electroluminescence material, but the fundamental role of proper phosphors is sometimes underestimated even when it is essential for an ideal color rendering. In this review, we analyze the main solid-state techniques for lighting applications, paying attention to the fundamental properties of phosphors to be successfully applied. Currently, the most widely used materials are based on rare-earth elements (REEs) whereas Ce:YAG represents the benchmark for white LEDs. However, there are several drawbacks to the REEs’ supply chain and several concerns from an environmental point of view. We analyze these critical issues and review alternative materials that can overcome their use. New compounds with reduced or totally REE free, quantum dots, metal–organic framework, and organic phosphors will be examined with reference to the current state-of-the-art.
Highlights
In recent years, light-emitting diode (LED) technology has reached high-quality standards and performance and competes with the traditional incandescent lamp as well as compact fluorescent lamps in terms of luminosity and ease of implementation
The spectral behavior of different LEDs strongly depends on the driving current and the chip temperature and should constantly be monitored
The first step consists of a focused overview of the requirements of phosphors for LED application with particular regard on the performance of Ce:YAG [31]: Emission spectrum: The emission spectrum of the phosphor is strictly connected to the pumping
Summary
Light-emitting diode (LED) technology has reached high-quality standards and performance and competes with the traditional incandescent lamp as well as compact fluorescent lamps in terms of luminosity and ease of implementation. LEDs present outstanding advantages over other lighting systems such as small size, high lifetime, high mechanical stability, and very high luminescence efficiency approaching the theoretical limits [1]. The spectral behavior of different LEDs strongly depends on the driving current and the chip temperature and should constantly be monitored These drawbacks do not permit the production and exploitation of RGB white LEDs for wide diffusion as well as in of those. Inconcentrated a few geographical and mining has a stronghas environmental impact For this reason, valid alternatives to REEs in photoelectronic devices with particular regard to lighting systems are strongly required. Advances in phosphors for LED application, with particular attention on the materials that substitute or strongly reduce the use of the rare-earth elements, is reported
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