Banca de QUALIFICAÇÃO: ORLANDO LUCAS DE LIMA CALADO

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : ORLANDO LUCAS DE LIMA CALADO
DATE: 27/08/2025
TIME: 14:00
LOCAL: Google Meet
TITLE:

Carbon dots and quantum dots acting as a conversion layer in light-emitting diodes

KEY WORDS:

Carbon Dots; Quantum Dots; Fluorescent films; light-emitting diode; dual emission; white emission;

PAGES: 70
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUMMARY:

White light-emitting diode (WLED) technology has established itself in the global illumination market due to its high efficiency, long lifespan, and sustainability. However, the conventional production of WLEDs still relies on color converters based on rare-earth compounds, which present significant disadvantages such as high cost, resource scarcity, and often a low color rendering index (CRI < 80). Facing this challenge, scientific research has turned to the development of alternative materials, and nanomaterials like Carbon Dots (CDs) and Quantum Dots (QDs) have emerged as promising platforms due to their high photostability and tunable optical properties. In this context, the present work addresses the development of composite systems based on CDs and QDs to act as efficient light converters in high-performance WLEDs. In a first approach, a converter system based exclusively on Carbon Dots from distinct sources was investigated. CDs were synthesized from neutral red dye with citric acid (Nr-CDs) and banana peel extract (B-CDs) using hydrothermal and microwave methods, respectively. Subsequently, these CDs were incorporated into a polyvinyl alcohol (PVA) matrix to produce films capable of converting UV/blue light into white light. Notably, the film combining both types of CDs (BNr-CDs-F) emitted high-quality white light with chromaticity coordinates (CIE) of (0.30, 0.32) (very close to pure white (0.33, 0.33)), a correlated color temperature (CCT) of 6669 K, and an excellent color rendering index (CRI) of 90. A WLED prototype, constructed by combining this film with a commercial LED chip, demonstrated a luminous intensity of 374 cd·m−2 (7 times higher than the commercial UV/blue LED chip) and a CRI of 95, validating the potential of the approach for developing low-cost, rare-earth-free devices. Aiming to explore a complementary
strategy and broaden the control over the emission spectrum, a second approach focused on the combination of CDs with QDs. In this study, UAC-CDs (blue-emitting CDs) and CdTe-QDs (orange-red emitting QDs) were synthesized and subsequently incorporated into a PVA matrix in different proportions (UACd-F-X; X=1-4). As a result, increasing the concentration of CdTe- QDs intensified the emission in the 550-700 nm range, shifting the CIE coordinates from the blue region (0.18, 0.20) to a point near standard white (0.28, 0.25). Consequently, the UACd-F-4 formulation demonstrated versatile white light emission with an adjustable CCT (from 9562 K to 5416 K) and a CRI greater than 80. The composite's efficacy was proven by fabricating a prototype where the film, when deposited onto a commercial LED chip, produced neutral white light (CCT of 5649 K) with CIE coordinates of (0.32, 0.30) and a CRI of 80. Therefore, the strategies investigated in this work have proven to be effective methods for fabricating light-converting films, as they show potential for applications in solid-state lighting devices, overcoming the limitations of conventional materials available on the market.

COMMITTEE MEMBERS:
Externo(a) à Instituição - Andreia de Morais
Presidente - 1869296 - CINTYA D'ANGELES DO ESPIRITO SANTO BARBOSA
Externo(a) ao Programa - ***.790.304-** - RODRIGO DA SILVA VIANA - UFAL
Interno(a) - 1515173 - SIMONI MARGARETI PLENTZ MENEGHETTI