Characterization of Pt4+ in alumino-metaphosphate laser glasses

The Pt ⁴⁺ optical spectra (16 600–50 000 cm ⁻¹ ) in a series of alkali/alkaline alumino-metaphosphate glasses are reported. The four observed spectral bands are assigned to the d–d transitions from the 1 A 1 g ground state to the 3 T 1 g (∼23 500 cm ⁻¹), 3 T 2 g (∼28 000 cm ⁻¹), 1 T 1 g (∼33 300 cm ⁻¹) and 1 T 2 g (∼40 000 cm ⁻¹) excited states assuming Pt ⁴⁺ resides in a distorted octahedral site. The absorption band intensities are found to exist in two groups, with the low compositionally averaged modifier field strength (<3.5 Å ⁻²) having the greater absorption intensities. The ligand splitting energy and Racah parameter B vary between ∼38 000 and 40 000 cm ⁻¹ and between ∼435 and 650 cm ⁻¹, respectively, depending on the choice of modifier. The Pt ⁴⁺ absorption coefficient, α, at 25 000 cm ⁻¹ is correlated with the platinum concentration (ppm _w ) in a potassium magnesium-alumino-metaphosphate glass by the equation: [Pt] ppm _w=526 α (cm ⁻¹ ). A comparison of relative Pt uptake during melting shows that the rare-earth doped potassium magnesium alumino-phosphate melt has the greatest uptake and is approximately 25 times greater than the concentration reported for the commercial silicate laser glass, ED-2. The effect of Pt ⁴⁺ (0–860 ppm _w) on fluorescence quenching rate from the Nd ³⁺ 4 F 3/2 state is small ( k _A≈0.3 Hz/ppm _w) in agreement with predictions based on the Förster–Dexter theory for dipolar energy transfer.