Phase-Selective Distribution of Eu²⁺ and Eu³⁺ in Oxide and Fluoride Crystals in Glass-Ceramics for Warm White-Light-Emitting Diodes

Abstract

High-power white-light-emitting diodes (WLEDs) comprising binderless bulk phosphors and ultraviolet (UV) LED chips as next-generation illumination sources were intensively studied. The main challenge is the effective management of different color components in each suitable crystal phase while maximizing their optical properties with near-UV excitation. In this regard, we developed glass-ceramics that contain Na5Gd9F32 and NaAlSiO4, in which the phase-selective distribution of Eu3+ and Eu2+ results in warm white-light emission with a low correlated color temperature (CCT) (< 3000 K), high color rendering index (Ra > 70), and promising thermal stability. The obtained composite exhibits broadband photoluminescence (PL) around the blue–green (NaAlSiO4:Eu2+) and red (Na5Gd9F32:Eu3+) spectral regions. Up to 573 K, the PL intensity remains above 50% of that at room temperature (RT). The internal PL quantum yield was estimated as 35%. Further, a thermal-aging test was conducted for 1000 h at 573 K, after which the sample exhibited 70.7% of the initial PL intensity at RT and showed stability in the chromaticity coordinate for a warm white range. This study, which exhibits potential for practical applications, provides a strategy for the generation of a warm white-light color with Eu2+ and Eu3+ in oxide and fluoride phases in combination with UV LEDs.

NaAlSiO4: Eu2+ Glass Ceramics: Self‐Reduced In Situ Growth and High‐Power LED/LD Lighting

“…In this case, the excitation and emission of Eu 2+ in glass are nonadjustable, owing to the disordered surroundings. Even though the NaAlSiO 4 (NSAO): Eu 2+ phosphors and the corresponding GCs have been reported previously, [39][40][41] their optical properties including luminescent efficiency and thermal stability are still dissatisfactory for the practical application in high-power LED/LD Herein, a series of Eu 2+ -doped NASO GCs are elaborately designed and fabricated according to an in situ glass crystallization strategy. With the help of structural and spectrographic characterization, it is evidenced that the high crystallization fraction and suitable structure of NASO crystals in glass are beneficial for the partition of the self-reduced Eu 2+ ions.…”

Site construction of Eu2+ and sensitized luminescence of Eu3+ in LaF3:Eu nanophosphor

“…9 White light emission is also easy to achieve by the combination luminescence of Eu 2+ and Eu 3+ . [10][11][12] However, low oscillator strength and narrow linewidth of 4f-4f absorption transitions of Eu 3+ have limited the application of Eu 3+ activated phosphors in many fields, especially in white LED lighting. One effective strategy is to find sensitizers for Eu 3+ luminescence that have allowed excitation bands that overlap with the typical emission wavelength of InGaN-based LEDs (∼360-470 nm).…”

“…This energy transfer pathway provides an alternative approach to explore novel phosphor suitable for lighting and display application. [10][11][12]15,16 According to the nominal chemistry formula La 1-x F 3 :xEu (x = 0.01-0.12), Citric acid and the rareearth ions (La 3+ and Eu 3+ ) were first mixed at the molar ratio of 1:1 in an aqueous solution and then mixed with NaF solution. The mixture was stirred evenly to form a white emulsion and then hydrothermally treated at a certain temperature.…”

Structural phase evolved Ni2+‐doped fluoride nanocrystals in KF−ZnF2−SiO2 glass‐ceramics

“…Tremendous attention has been paid to optical oxyfluoride glass ceramics (GCs) because of their unique comprehensive characteristics of low phonon energy of fluoride crystals, but also favorable mechanical properties and durability of oxide glasses. In particular, through the precipitation of rare earth ions (REIs) and transition metal ions (TMIs)‐doped fluoride nanocrystals (NCs), oxyfluoride GCs have developed potential photoluminescence (PL) and laser applications, including optical waveguide, 1 noninvasive medical diagnostics, 2 optical signal detector, 3,4 white LED, 5‐7 laser cooling, 8 and broadband optical amplifiers in the whole telecommunication window 9,10 . Thus, the design and fabrication of suitable oxyfluoride GCs is meaningful in glass engineering field.…”

“…DING et al nanocrystals (NCs), oxyfluoride GCs have developed potential photoluminescence (PL) and laser applications, including optical waveguide, 1 noninvasive medical diagnostics, 2 optical signal detector, 3,4 white LED, [5][6][7] laser cooling, 8 and broadband optical amplifiers in the whole telecommunication window. 9,10 Thus, the design and fabrication of suitable oxyfluoride GCs is meaningful in glass engineering field.…”