Characterization of Pt4+ in alumino-metaphosphate laser glasses

The Pt4+ 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 1A1g ground state to the 3T1g (∼23 500 cm−1), 3T2g (∼28 000 cm−1), 1T1g (∼33 300 cm−1) and 1T2g (∼40 000 cm−1) excited states assuming Pt4+ 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 Pt4+ absorption coefficient, α, at 25 000 cm−1 is correlated with the platinum concentration (ppmw) in a potassium magnesium-alumino-metaphosphate glass by the equation: [Pt] ppmw=526α (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 Pt4+ (0–860 ppmw) on fluorescence quenching rate from the Nd3+ 4F3/2 state is small (kA≈0.3 Hz/ppmw) in agreement with predictions based on the Förster–Dexter theory for dipolar energy transfer.