The cyan-emitting BaSi₂O₂N₂:Eu²⁺ phosphor is a promising narrow-band and high-efficiency luminescent material used in wide-color-gamut white light-emitting diodes (wLEDs). However, its serious degradation under thermal attacks hinders its practical applications and needs to be improved. Herein, we proposed to deposit a nano-sized Al₂O₃ film around each BaSi₂O₂N₂:Eu²⁺ particle through atomic layer deposition (ALD) in a fluidized bed reactor to improve its thermal stability. Thermal gravimetric analysis results showed that the Al₂O₃ layer with a thickness of only 11 nm had an obvious anti-oxidization effect, by which the oxidation temperature in air of the Al₂O₃ coated phosphor was largely increased from ∼550 to ∼750 °C. Moreover, the Al₂O₃ coated phosphor remained 93% of its luminescence intensity in comparison to 73% of the uncoated one when degraded under water-steam at 200 °C for 24 h. The oxidization of both the BaSi₂O₂N₂ host matrix and the doped Eu²⁺ ions was reduced by the Al₂O₃ layer. Meanwhile, the wLEDs fabricated with the Al₂O₃ coated phosphor showed a luminous flux of 3 times higher than that of the uncoated one when aged under 100 mA for 300 h. The greatly improved thermal degradation property of BaSi₂O₂N₂:Eu²⁺ phosphor and the reliability of the wLEDs indicate that the ALD approach could be a feasible route to produce uniform and nano layers on phosphors and enhance their stability.

Residual stresses and distortions are major obstacles against the more widespread application of wire arc additive manufacturing. Since the steep temperature gradients due to a moving localised heat source are inevitable in this process, accurate prediction of the thermally induced residual stresses and distortions is of paramount importance. In the present study, a computationally efficient thermo-mechanical model based on a semi-analytical thermal approach incorporating Goldak heat sources is developed for the process modelling of wire arc additive manufacturing. The semi-analytical thermal model makes use of the superposition principle, and thereby decomposes the temperature field into an analytical temperature field to account for the heat sources in a semi-infinite space and a complementary temperature field to account for the boundary conditions. Since the steep temperature gradients are captured by the analytical solution, a coarse spatial discretisation can be used for the numerical solution of the complementary Tˆ field. Thermal evolution is coupled to an elasto-plastic mechanical boundary value problem that computes the thermal stresses and distortions. The accuracy of the proposed model is evaluated extensively by comparing the thermal and mechanical predictions with the corresponding experimental measurements as well as the simulation results obtained by a non-linear transient model from the literature. A thin wall structure with a length of 500 mm and consisting of 4 layers is modelled. The peak normal stress along the deposition direction can be predicted with less than 10% error. Furthermore, the simulations show that the part distortions are very sensitive to the boundary conditions.