Highly Thermal Stable Broadband Near-Infrared Luminescence in Ni2+-Doped LaAlO3 with Charge Compensator

Ni2+-doped LaAlO3 perovskite ceramic samples with a charge compensator (M4+) were prepared and their luminescent properties were investigated. The LaAlO3:Ni2+–M4+ (M = Sn, Hf, Ti, Zr) perovskites show a broad near-infrared (NIR) luminescence peaking at around 1070 nm with 150 nm fwhm due to the Ni2+:3T2-3A2 transition. The Sn4+-codoped one showed the highest NIR luminescence intensity. The valence state of major Ni ions is changed from Ni3+ to Ni2+ by codoping with Sn4+ based on X-ray absorption spectroscopy. The LaAlO3:Ni2+–Sn4+ shows the shortest luminescence peak wavelength (λem = 1070 nm) at 300 K due to the strong crystal field and also shows the highest quenching temperature, T50% of 608 K in the temperature dependence of PL intensity, due to the largest activation energy among the Ni2+-doped NIR phosphors ever reported. Based on the positive trend in the plot of T50% vs PL peak energy, it is concluded that the dominant quenching process in almost all Ni2+ phosphors is the thermally activated crossover process. It is also demonstrated that the luminescence peak wavelength is shifted from 1070 to 1235 nm continuously by substituting Ga ions for the Al site.