Charge compensation effect of alkali metal ions on luminescence enhancement and negative thermal quenching of Sr1-xLaNaTeO6:xEu3+ red phosphors

Abstract

A series of novel phosphors, specifically Eu3+-doped and Eu3+/M+ co-doped (M = Li+, Na+, K+) SrLaNaTeO6, were synthesized via a high-temperature solid-state process. The luminous properties and thermal stability of these phosphors were thoroughly investigated. When subjected to the appropriate excitation wavelengths (395 and 465 nm), all phosphors demonstrate a pronounced red light emission, corresponding to the 5D0→7F2 transition of Eu3+. The researchers found that the most effective concentration of Eu3+ doping in the Sr1-xLaNaTeO6:xEu3+ phosphor was discovered to be x = 0.25. It was shown that excessive doping leads to concentration quenching, which can be attributed to the energy transfer interaction between Eu3+ ions. The incorporation of Li+, Na+, and K+ as charge compensation ions in conjunction with Eu3+ in Sr0.75LaNaTeO6:0.25Eu3+ phosphor leads to a notable enhancement in light intensity. Notably, the phosphor co-doped with Na+ exhibits the highest luminous intensity among the alkali metal charge compensation ions. The near proximity of the ion radius of the charge compensation ion Na+ to that of Sr2+ in the host facilitates the occupation of the Na + ion in the Sr2+ lattice location. Sodium ions (Na+) have the ability to counteract the positive defects resulting from the substitution of europium ions (Eu3+) with strontium ions (Sr2+), hence maintaining charge neutrality. Additionally, it should be noted that Sr0.5LaNaTeO6:0.25Eu3+,0.25Na+ phosphor exhibits a remarkable quantum yield of 71.26 % and lacks thermal quenching. These characteristics suggest that this particular phosphor holds promising potential for utilization in developing white-light-emitting diodes.