Key Mass Production Issues and Comprehensive Mitigation Strategies for PiG (Phosphor-in-Glass) (First Item)

Thermal quenching & sharp drop in quantum efficiency
Conventional borosilicate/tellurite glass requires sintering at 550~850°C. Nitride red phosphors (CaAlSiN₃, SrLiAl₃N₄) and KSF fluorosilicate phosphors exhibit poor heat resistance. At high temperatures, luminescent center ions (Ce³⁺, Eu²⁺) undergo oxidation and valence state transformation, directly reducing luminous efficacy by 20%~50%. Although YAG:Ce features superior thermal resistance, interionic diffusion at the glass-phosphor interface still degrades quantum efficiency.

Interfacial corrosion between glass and phosphors & generation of impurity phases
Si⁴⁺, Na⁺ and B³⁺ from glass diffuse into YAG particles; Y³⁺ and Al³⁺ from YAG dissolve into the glass matrix, forming dozens-of-nanometer-thick non-luminescent impurity diffusion layers. These layers block light conversion, increase light scattering and trigger correlated color temperature drift.

Accelerated phosphor hydrolysis degradation induced by alkali metals
Alkali metal oxides (Li₂O, Na₂O, K₂O) inside glass migrate to the material surface under long-term damp-heat conditions (85°C / 85%RH), damaging the crystal lattice of nitride phosphors and resulting in severe long-term light decay and color coordinate shift.

• Diffusion-matched low-interdiffusion glass system: Introduce phosphor homologous elements (Y₂O₃, Al₂O₃) into glass to reduce interfacial concentration gradients, confine the diffusion layer thickness within 50 nm and retain over 95% of the original quantum efficiency of raw phosphors.
• Low-alkali / alkali-free glass: Replace alkali metals with ZnO, CaO and BaO to reduce Na₂O and Li₂O content and improve damp-heat reliability. Low-temperature fluorophosphate glass dedicated to nitride phosphors only requires sintering at 350~500°C, completely eliminating thermal decomposition of red nitride phosphors.
• Glass with high Tg and narrow softening temperature window: Narrow the temperature range between softening and crystallization to shorten high-temperature holding duration.

• Rapid Thermal Annealing (RTA) / induction pressure sintering: Adopt a heating rate of 20~50°C/s to complete densification within tens of seconds, drastically cutting high-temperature exposure time. The resultant diffusion layer is only 1~2 nm thick, which significantly mitigates luminous decay of nitride PiG.
• Step heating & holding temperature profile: Low-temperature debinding (sufficient removal of moisture and organic substances at 300~400°C) → rapid heating to softening temperature → short holding period (5~30 min) → slow cooling, avoiding prolonged high-temperature soaking of phosphors.
• Atmosphere-protected sintering: High-purity nitrogen / inert atmosphere furnaces are mandatory for nitride and KSF phosphors to isolate oxygen and water vapor and prevent Eu²⁺ oxidation. YAG can be sintered in air; nitrogen protection is still recommended for high-spec products.

• Coat phosphor surfaces with a 50~200 nm protective layer of SiO₂, Al₂O₃ or homogeneous YAG material. The coating forms a barrier layer to block ionic interdiffusion and isolate corrosion from molten glass.