Enhancement of thermal stability and reliability of Ba_xSr_2−xSiO₄:Eu²⁺ phosphors by Ba²⁺ doping

Ba_xSr_2−xSiO₄:0.02Eu²⁺ (x = 0, 0.2, 0.5, 0.8, 1, 1.5 and 2) phosphors were synthesized by high temperature solid-state reaction. The effect of Ba²⁺ doping on the thermal stability and reliability properties of the phosphors were investigated. The photoluminescence (PL) emission bands of Ba_xSr_2−xSiO₄:0.02Eu²⁺ showed blue shift from 576 to 508 nm with increasing Ba content under excited at 460 nm. As x value is more than 1, the thermal stability of Ba_xSr_2−xSiO₄:0.02Eu²⁺ phosphor is decreased significantly. As the temperature increases from 300 to 500 K, PL intensity of Ba_xSr_2−xSiO₄:0.02Eu²⁺ phosphor decreases by 91.32, 80.26, 64.80, 69.91 and 94.12 % of the initial PL intensity for x = 0, 0.5, 1, 1.5 and 2, respectively. The thermal cycling testing results show that the relative PL intensity of Ba_xSr_2−xSiO₄:0.02Eu²⁺ phosphor decrease to 84.08, 85.99, 90.18, 92.59, 94.89, 90.88 and 85.42 % with x value is 0, 0.2, 0.5, 0.8, 1, 1.5 and 2 after storing the phosphors into an ambient condition of 120 °C for 1 h and −40 °C for 1 h by turns for five times. Reliability test results show that the relative PL intensity of Ba_xSr_2−xSiO₄:0.02Eu²⁺ phosphor decrease to 83.90, 92.36, 93.88, 95.89, 95.85, 93.47 and 85.03 % with x value is 0, 0.2, 0.5, 0.8, 1, 1.5 and 2 after the ambient condition of 85 °C/RH 85 % for the exposure time of 168 h; The relative PL intensity of Ba_xSr_2−xSiO₄:0.02Eu²⁺ phosphor decrease to 75.23, 83.63, 85.76, 89.58, 88.28, 85.03 and 70.97 % with x value is 0, 0.2, 0.5, 0.8, 1, 1.5 and 2 after soaking into boiled water for 3 h. It can be summarized that the addition of Ba with the x value less than 1 could increase the thermal stability largely and enhance the reliability of Ba_xSr_2−xSiO₄:0.02Eu²⁺ phosphors remarkably.