Potential substitutes for critical materials in white LEDs: Technological challenges and market opportunities

White light emitting diodes (wLEDs) have become, in the last decade, the most efficient device for most lighting applications. They are mainly composed of indium and gallium for the blue emitting LED, and rare-earth elements for the phosphor producing the yellow component of the white light. Those elements are crucial to achieve the excellent lighting properties of wLEDs, but they are systematically ranked among the most critical materials. In the present review, the essential roles of indium, gallium and rare-earth elements in wLEDs are specified, and their criticality through the main criteria of supply shortage risk and economic importance is discussed in detail in the light of the wLED market. The opportunities and technological challenges of their reduction using nano sized objects and substitution using non-critical materials are considered in relation to the resulting changes in the performance of wLEDs, but also to the stated preference of consumers of the final product, creating an opportunity for trade-offs between the performance and avoidance of critical materials in wLEDs. The economic value that a consumer could place in a critical material-free wLED is further estimated through a choice experiment conducted with 297 consumers. The results obtained show a positive, significant willingness to pay for critical material-free wLEDs. On average, consumers are ready to pay ?2.82 more for a wLED sold at ?10. The present approach addresses the transdisciplinary problem of the reduction and substitution of critical materials in functional devices intended for consumers, and can be generalized to other energy-related materials and devices.