1.5‐μm infrared excitation of visible luminescent in Y1−xErxF3 and Y1−x−yErxTmyF3 via resonant‐energy transfer

Intense visible emission in the red, green, and blue has been observed from infrared to visible multiphoton Y1−xErxF3 upconversion phosphors pumped with 1.5‐μm radiation from InGaAsP‐laser sources. With 0.01<x<0.2, the dominant emission is in the green corresponding to transitions from the 4S3/2 level of Er3+. The addition of Tm3+ in the 0.001–0.02 range preferentially quenches the emission from the higher‐energy Er3+ levels resulting in a red visible emission originating on the Er3+ 4F9/2 level. The phosphors are useful visible monitors of focused 1.5‐μm semiconductor laser and unfocused F‐center laser radiation. The unexpectedly high brightness in the visible may be attributed to thermal equilibration, where the excitation is trapped in the higher lying states after each upconversion step.

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