Phosphor-converted and quantum-dot-converted LEDs represent advanced lighting technologies that enhance color performance and efficiency in solid-state lighting. These designs leverage luminescent materials to convert high-energy photons into desired wavelengths, enabling precise control over emission spectra. The following discussion explores their architectures, remote phosphor configurations, and color rendering metrics.

Phosphor-converted LEDs (pc-LEDs) utilize phosphor materials to partially or fully convert blue or ultraviolet (UV) light from a semiconductor chip into longer wavelengths. The most common design involves a blue LED chip coated with a yellow-emitting phosphor, such as cerium-doped yttrium aluminum garnet (YAG:Ce). This combination produces white light through partial conversion, where residual blue light mixes with yellow emission. For higher color quality, multiple phosphors with complementary emissions (e.g., red and green) are employed to broaden the spectrum. The phosphor layer is typically dispersed in a silicone or epoxy matrix and applied directly onto the chip or the surrounding package.

Remote phosphor configurations decouple the phosphor layer from the LED chip, placing it at a distance within the optical system. This design reduces thermal quenching, as heat generated by the chip does not directly degrade the phosphor. It also improves light extraction and color uniformity by minimizing localized intensity variations. Remote phosphor systems often use a blue LED array with a separate phosphor plate or dome, enabling modularity and easier thermal management. The phosphor plate may incorporate scattering particles to enhance mixing and reduce angular color deviation.

Quantum-dot-converted LEDs (QD-LEDs) replace or supplement phosphors with semiconductor nanocrystals (quantum dots) that exhibit size-tunable emission. Quantum dots offer narrow emission bands, typically with full-width-at-half-maximum (FWHM) values below 30 nm, enabling precise spectral control. In a typical QD-LED, a blue LED excites red- and green-emitting quantum dots, which are either embedded in a film or dispersed in a polymer matrix. The film may be applied directly to the chip (on-chip configuration) or positioned remotely (remote QD configuration). Remote QD designs mitigate thermal and photodegradation, as quantum dots are sensitive to high temperatures and prolonged UV/blue exposure.

Color rendering metrics evaluate how accurately a light source reproduces object colors compared to a reference illuminant. The Color Rendering Index (CRI) is a widely used metric, with a maximum value of 100 indicating perfect fidelity. pc-LEDs with single phosphors often achieve CRIs around 70–80, while multi-phosphor systems exceed 90. QD-LEDs can achieve CRIs above 95 due to their narrow emissions, which closely match the spectral features of natural light. However, CRI has limitations, as it only assesses eight pastel test colors. The newer TM-30 metric evaluates 99 color samples and provides additional measures, such as fidelity index (Rf) and gamut index (Rg). High-fidelity QD-LEDs typically achieve Rf values above 90, with Rg values indicating moderate to high saturation.

Efficiency considerations include luminous efficacy (lumens per watt) and quantum efficiency (photons emitted per photon absorbed). pc-LEDs with YAG:Ce exhibit high quantum efficiency (>90%) but suffer from Stokes energy loss due to the large wavelength shift. Narrow-band red phosphors (e.g., europium-doped nitrides) improve efficacy but are less efficient than yellow phosphors. QD-LEDs face challenges with quantum dot stability and absorption efficiency, though advances in core-shell structures and encapsulation have improved performance. Remote configurations in both pc-LEDs and QD-LEDs reduce thermal degradation, extending lifetime but may introduce additional optical losses.

Phosphor and quantum dot materials must meet stringent requirements for stability, efficiency, and manufacturability. Phosphors for pc-LEDs include garnets, silicates, and nitrides, each with distinct thermal and chemical stability profiles. Quantum dots for LEDs are typically cadmium-based (e.g., CdSe) or cadmium-free (e.g., InP), with the latter gaining prominence due to environmental regulations. Encapsulation materials must resist yellowing under UV exposure and maintain mechanical integrity over time.

Applications of these technologies span general lighting, displays, and specialty illumination. High-CRI pc-LEDs dominate architectural and retail lighting, where color accuracy is critical. QD-LEDs are increasingly used in liquid crystal display (LCD) backlights, enabling wider color gamuts exceeding 90% of the BT.2020 standard. Remote phosphor systems are favored in high-power applications, such as automotive headlights and stadium lighting, where thermal management is paramount.

Future developments focus on improving material stability, reducing cost, and enhancing spectral precision. Phosphor discovery efforts target narrow-band red emitters with high efficiency, while quantum dot research emphasizes non-toxic alternatives and improved photoluminescence quantum yield. Advanced optical designs, such as patterned phosphor layers and hybrid QD-phosphor systems, aim to further optimize color quality and efficiency.

In summary, phosphor-converted and quantum-dot-converted LEDs offer versatile solutions for high-quality lighting, with distinct advantages in color rendering and efficiency. Remote configurations address thermal and optical challenges, while advanced metrics like TM-30 provide comprehensive performance evaluation. Continued material and design innovations will drive broader adoption across lighting and display applications.