Rapid synthesis of phosphor-glass composites in seconds based on particle self-stabilization

The study addresses the challenge of synthesizing phosphor-glass composites (PGC) rapidly while preserving the integrity and luminescence of embedded rare-earth phosphors such as YAG:Ce. Conventional polymer-encapsulated color converters degrade under heat, humidity, and high-energy light, and all-inorganic ceramics/crystals are costly and difficult to scale. Existing PGC methods often require long sintering times, causing thermal erosion and performance degradation. The research proposes a seconds-scale synthesis based on a particle self-stabilization mechanism in low-melting, low-viscosity tellurite glass to achieve dense, uniform dispersion of phosphor particles without interfacial reactions, aiming to deliver high-efficiency, stable photonic converters suitable for high-power laser-driven lighting.

Prior efforts to improve phosphor composites focused on (i) lowering synthesis temperature via low-sintering ceramics (e.g., CaF₂, hydroxyapatite) and low-melting glasses (tellurite, phosphate), often combined with hot isostatic pressing, gas pressure sintering, or spark plasma sintering to limit interfacial reactions; and (ii) selecting matrices (including silica) that intrinsically suppress interfacial reactions. Despite such advances, most glass/ceramic composites require lengthy processing to form bulk materials, leading to thermal erosion and luminescence losses. There is a recognized need for fast synthesis capable of forming PGC within seconds to protect phosphor integrity and reduce manufacturing cost and energy.

Materials and glass matrix: Tellurite glass composition 75TeO₂–15ZnO–10Na₂O (mol%) was selected for its low melting point and viscosity (0.1564–0.0373 Pa·s at 600–800 °C) due to high cation polarizability (Te⁴⁺, Zn²⁺). Glass was prepared by melt-quenching (700 °C, 40 min), crushed to powders, then remelted at 650 °C for 40 min in a corundum crucible for clarification. Rapid PGC synthesis: Commercial YAG:Ce phosphor particles (2–20 wt%) were poured into the clarified tellurite melt at 650 °C. The melt was agitated with a quartz rod for about 3–5 s to disperse particles uniformly, then the mixture was rapidly quenched to form bulk and annealed at 280 °C to remove internal stress. The total dispersion plus quench time was about 10 s. The approach can form various shapes, including fibers, via different quenching/forming processes. Comparative samples: YAG:Ce in silicone resin (YAG:Ce-PiS, 10 wt%) was prepared by mixing phosphor with silicone A/B, degassing, casting into a disk mold, and curing at 100 °C for 3 h. A commercial YAG:Ce phosphor-in-glass (YAG:Ce-PiG) was used for benchmarking. Characterization: Microstructure and interfaces were probed via XRD (phase purity), Raman (local structure), HRTEM/SAED and HAADF-STEM with EDS line mapping (interfacial diffusion), optical microscopy and CLSM 3D reconstruction (particle dispersion), transmission spectra (transmittance), PL/PLE and decay (luminescence), absolute QE and absorption (integrating sphere), temperature-dependent PL, thermal conductivity (laser flash), surface tension, viscosity, refractive index (prism coupler), dielectric constant, and TG-DSC of precursor glass. Simulation of dispersion: ANSYS Fluent with SST k–ω turbulence and discrete phase model simulated particle motion in the low-viscosity melt under agitation speeds of 1–5 rev s⁻¹, modeling YAG:Ce particles (~10.8 µm, 4700 kg m⁻³) injected for 1 s into tellurite melt (density 5020 kg m⁻³, viscosity 0.08693 kg·m⁻¹·s⁻¹). Simulations showed uniform filling throughout the fluid within 3–5 s at 5 rev s⁻¹, consistent with experiments. Self-stabilization model: The dispersion stability arises from the interplay of (i) a high interfacial energy barrier due to good wettability (contact angle 43.5° at 923 K) between tellurite melt and YAG:Ce, preventing atomic-scale contact/sintering; (ii) attractive van der Waals interaction between particles; and (iii) thermal energy aiding dispersion. Quantitatively, at 923 K: W_barrier ≈ 6.94 × 10⁻²⁰ J; thermal energy k_BT ≈ 12.74 zJ; van der Waals minimum attraction W_vdW(min) ≈ 2.42 × 10⁻²¹ J. The barrier far exceeds attractive/thermal energies, enabling self-stabilization even without agitation for extended times. Extended systems: The generality was validated by fabricating LuAG:Ce-PGC and GdAG:Ce-PGC using the same rapid strategy, yielding high IQE (>94%).

• Rapid fabrication: Dense, uniform YAG:Ce particle dispersion in tellurite glass achieved within ~10 s via agitation and quenching at 650 °C.
• Self-stabilization mechanism: Good wettability (contact angle 43.5° at 923 K) generates a large interfacial energy barrier (~6.94 × 10⁻²⁰ J) that prevents atomic-scale contact/sintering; this dominates over van der Waals attraction (W_vdW(min) ≈ 2.42 × 10⁻²¹ J) and thermal energy (k_BT ≈ 12.74 zJ), enabling dispersion stability even after holding the melt ~120 s without agitation.
• Microstructure/integration: XRD shows only YAG phase; Raman spectra are a superposition of tellurite glass and YAG:Ce; HRTEM/SAED and HAADF-STEM/EDS reveal a sharp interface with negligible interdiffusion (contrasting prior 50–300 nm reaction layers). Particle size remains ~10 µm after embedding; refractive index difference Δn ≈ 0.13 (n_glass ≈ 1.97, n_YAG ≈ 1.84); transmittance ~40% at 10 wt% loading.
• Optical performance: PLE bands at ~343 and 450 nm; PL centered at 552 nm (Ce³⁺ 5d–4f). YAG:Ce-PGC retains PL decay kinetics of powder. Absolute IQE ≥92% with absorption ≥85% across loadings; best IQE 98.4% and absorption 86.8%. YAG:Ce powder IQE 99.4%, absorption 74.5%.
• Laser-driven white light: Maximum luminous flux 1227 lm; peak luminous efficiency 276 lm W⁻¹ (prior to saturation); saturation threshold ~8.5 W mm⁻². Performance surpasses commercial YAG:Ce-PiG reference.
• Thermal properties and stability: Thermal conductivities of 1.52 W m⁻¹ K⁻¹ (RT) and 1.78 W m⁻¹ K⁻¹ (250 °C), ~7× silicone resin. Maintains 96% PL intensity at 150 °C vs 30 °C. Under 2 W mm⁻² continuous blue laser, YAG:Ce-PGC retains ~95% output after 7.5 h (vs ~93% for PiG), while PiS fails within 30 s.
• Generality and form factor: Strategy extends to LuAG:Ce and GdAG:Ce PGC with IQE >94%. The method is compatible with various shapes, including fibers.

The work demonstrates that controlling interfacial energetics via favorable wettability in a low-viscosity, low-melting tellurite glass enables a substantial interfacial energy barrier that suppresses particle-particle contact and sintering during processing. This mechanism, corroborated by theory and microscopy, addresses the core challenge of preserving phosphor integrity while achieving dense, uniform dispersion rapidly, thereby minimizing thermal erosion typical of long-duration sintering. The resulting composites exhibit high absorption and near-unity internal quantum efficiency, translating to strong laser-driven white-light performance with high luminous flux and efficiency, improved thermal management, and long-term operational stability. The concept is general, as evidenced by similarly high-efficiency LuAG:Ce and GdAG:Ce PGCs, and is compatible with diverse geometries (e.g., fibers), underscoring relevance for high-power solid-state lighting and other photonic applications.

A fast, agitation-assisted synthesis in tellurite glass achieves phosphor-glass composites in about 10 seconds by leveraging a particle self-stabilization mechanism driven by good wettability and a high interfacial energy barrier. The process yields uniform, dense dispersions with negligible interfacial reactions, preserving the intrinsic luminescence of YAG:Ce and delivering high IQE (up to 98.4%), strong absorption (86.8%), and excellent laser-driven white-light performance (1227 lm, 276 lm W⁻¹) with robust thermal and operational stability. The approach generalizes to other garnet phosphors (LuAG:Ce, GdAG:Ce) and supports varied form factors, offering a scalable, energy-efficient route to functional glass composites for lighting and detection. Future work could optimize porosity and color rendering at higher phosphor loadings, expand phosphor/matrix combinations, and refine thermal management for higher saturation thresholds.

• Emission saturation occurs at high laser power density due to heat accumulation, indicating thermal management limits under extreme excitation.
• Higher phosphor loadings (10–15 wt% and above) can introduce porosity and abrupt changes in CRI/CCT, suggesting processing optimization is needed to control defects at elevated loadings.
• The demonstrated mechanism and parameters are established for tellurite glass with specific wettability; generalization to other glass systems may require tuning surface energies and processing conditions.
• Reported thermal conductivity, while higher than polymers, remains modest compared to some ceramics, potentially constraining ultimate power handling without additional heat sinking.