IR luminescence of thulium-activated crystals of double sodium yttrium fluoride Na0.4Y0.6F2.2:Tm3+: Self-quenching of luminescence from the 3H4 level

Na0.4Y0.6F2.2:Tm3+ crystals with thulium contents of 0.5–20% have been grown by the Stockbarger-Bridgman method. The concentration dependences of the steady-state spectra and luminescence kinetics from the 3H4 and 3F4 thulium levels upon selective laser excitation of a series of Na0.4Y0.6F2.2:Tm3+ crystals (0.5–20% Tm) are investigated. It is shown that the luminescence from the 3H4 level becomes significantly quenched with an increase in the concentration due to the nonradiative energy transfer. No concentration quenching of luminescence from the 3F4 level is observed. Possible schemes of self-quenching are considered for the 3H4 thulium level, the self-quenching microparameters and macrorates are estimated using model quantum-mechanical calculation, and the most likely self-quenching mechanisms and schemes are found from comparison of the calculated and experimental self-quenching rates. Good agreement is obtained between the experimental and calculated kinetic curves. It is shown that, under pumping near ∼0.8 μm, self-quenching of the 3H4 thulium level leads to effective occupation of the 3F4 level and increases the luminescence intensity in the range of 1.7–1.9 μm. It is concluded that Na0.4Y0.6F2.2:Tm3+ crystals are promising active media for tunable lasers in the range of 1.7–1.9 μm, with small thermal loss under laser-diode pumping near 0.8 μm.