Synthesis, structure and photoluminescence properties of NIR phosphor LiAlSi2O6:Cr3+

A novel Cr3+-doped LiAlSi2O6 phosphor was synthesized by a solid-state reaction. Details of first-principles calculation, structural studies, spectroscopic, crystal field calculations along with photoluminescence thermal stability for Cr3+ doped LiAlSi2O6 are given in the present paper. First-principles calculations show beta-LiAlSi2O6 has the lowest formation free energy in alpha 1-, alpha 2-, beta-and gamma-LiAlSi2O6 and is the indirect band gap. The XRD pattern indicates that the sample is beta-LiAlSi2O6. The excitation spectrum of LiAlSi2O6:Cr3+ peaking at 254, 411 and 561 nm corresponded to three spin-allowed Cr3+ d-d intra-shell transitions of 4A2g-4T1g(4P), 4A2g-4T1g(4F) and 4A2g-4T2g(4F), respectively. The reason for the change of the emission peak observed between the ultra-trace doping sample and the actively doped sample is discussed. Cr doping increases the disorder degree of cations in LiAlSi2O6 and makes the possible emission of Cr due to mainly N line emission. The Tanabe-Sugano diagram shows that Cr doping increases the strength of LiAlSi2O6 crystal field. The emission intensity of LiAlSi2O6:0.15% Cr3+ at 423 K (150 degrees C) maintains approximate to 70.0% of its initial value at 303 K (30 degrees C). Only the sharp emission line of the 2Eg-4A2g related transitions even at high temperatures (T = 523 K) and no large increase of the PL intensity caused by the odd-parity phonon gaining over the wide range of temperature from T = 303 K-523 K.