Effect of Pr ion concentration on the luminescence properties of NaCl:0.01Ce3+,Pr3+ crystals grown in large size

Highlights: • Large size NaCl:0.01Ce³⁺,XPr³⁺ crystals with high quality were grown by the Czochralski method. • The energy transfer mechanism from Ce³⁺ to Pr³⁺ ions in the NaCl host has been described. • The luminescence (both PL and TL) performance of NaCl:0.01Ce³⁺,XPr³⁺ crystals is maximum at X = 0.008. Large size single crystals of NaCl:Ce³⁺,XPr³⁺ (with X = 0.0, 0.002, 0.005, 0.008, 0.02, 0.05 and 0.08) were successfully grown by the melt (Czochralski) method and characterized structurally and optically. X-ray diffraction analysis has revealed the incorporation of Ce³⁺ and Pr³⁺ ions into the NaCl matrix and the creation of vacancy centers (V_Na) and positive defects (Ce_Na^●● and Pr_Na^●●) to keep the charge balance. Optical absorption spectral analysis has indicated the presence of absorption peaks at 214, 225, 305, 342, 446, 469, 483 and 592 nm. Photoluminescence (PL) spectral analysis (excited with 259 nm) has revealed dominant emission peaks at 386 and 390 nm due to 5d→4f transition of Ce³⁺ ions and sharp lines at 479, 491, 532, 600 and 621 nm due to ³P₁→³H₄, ³P₀→³H₄, ³P₁→³H₅, ³P₀→³H₆ and ³P₀→³F₂ transitions of Pr³⁺ ions. The energy transfer mechanism from Ce³⁺ to Pr³⁺ in the NaCl crystal has been described and the color coordinates of the luminescence of NaCl:Ce³⁺,XPr³⁺ crystals have been calculated by using the emission spectral data. The thermo-luminescence (TL) glow curves of NaCl:Ce³⁺,XPr³⁺ crystals obtained show three peaks at about 83, 150 and 239 °C, suitable trap depths induced by Ce³⁺ and Pr³⁺ and resulted in the characteristic emission. The TL mechanism of NaCl:Ce³⁺,XPr³⁺ crystals has been discussed. The photoluminescence and thermo-luminescence performances have been found to depend strongly on the Pr ion concentration and the maximum intensity has been obtained for the crystal with X = 0.008. Also, the increase in Pr ion concentration has led to gradual decrease of luminescence decay time.