Improving Optical Efficiency and Durability With Solid–Liquid Mixed Gels in Ultraviolet Light-Emitting Diodes

Ultraviolet light-emitting diodes (UV-LEDs) are considered to be the most promising ultraviolet light sources for effective and fast medical treatment and sterilization. However, it remains challenging to promote the light extraction and durability of UV-LEDs owing to the strong UV light absorption of conventional encapsulation materials. In this article, solid-liquid mixed gels (SLMGs) are proposed to fabricate transparent organic encapsulants for UV-LEDs, largely enhancing the optical efficiency and durability. The solid-state cross-linked networks of polydimethylsiloxane in the SLMG structure are utilized to maintain the liquid components of silicone oil and thus exhibited excellent UV transparency (over 90% in the UV range), which is comparable to that of quartz glass. The radiant efficiency of the UV-LED device can be significantly enhanced, increasing from 44.2% to 52.6% when using SLMGs, and the near-field emission angle achieves an increment of approximately 20°. Furthermore, the average UV transmittance of SLMG composites remains above 95% and does not exhibit cracking or yellowing phenomena under high temperature and UV irradiation for continuous aging of 1500 h. The harsh device aging tests demonstrate that SLMGs exhibits excellent thermal stability and UV radiation resistance, which is comparable to the device with all-inorganic encapsulation, achieving an average operational lifetime over 22 000 h. Therefore, this study provides a feasible and effective method of enhancing the optical performance and durability of UV-LEDs, advancing their promising potential applications.