Luminescence from Ti2+ ions in LiF crystals

Luminescence of Ti²⁺: LiF crystals in the wavelength range 650–900 nm excited using laser radiation is reported. The values of 10Dq and the Racah B parameter obtained from the present results indicate that in LiF the ¹ E, ¹ T ₂, and ³ T ₂ energy levels are almost at the cross-over point in the Tanabe-Sugano diagram. In consequence photoluminescence from all three energy levels to the ground state is observed. At low temperature (T 14 K) the emission is mainly due to sharp emission lines with weak vibronic structure due to the ¹ E, ¹ T ₂³ T ₁ transitions of Ti²⁺ ions. The ³ T ₂³ T ₁ broad-band emission is weak at low temperature, becoming stronger at 300 K due to a phonon-assisted tunnelling process, similar to that observed in Cr³⁺: garnets 1]. The excitation spectrum of these lines is a broad peak at 590 nm due to absorption in the ³ T ₁³ T ₂ transition.