Based on the molecular energy transfer mechanism, relative gains at 1067 and 637 nm wavelengths are achieved in thermally activated delayed fluorescence molecule AQ(PhDPA)2 and Nd complex with chelating phosphine oxide as ligands codoped polymer waveguides, with the excitation of low‐power UV light‐emitting diodes (LEDs) instead of traditional semiconductor lasers as pump sources. For AQ(PhDPA)2‐Nd(DBTTA)3(DBFDPO) (DBTTA = dibenzotetrathienoacene, DBFDPO = 4,6‐bis (diphenylphosphoryl) dibenzofuran) ‐codoped polymethylmethacrylate (PMMA), and AQ(PhDPA)2‐Nd(DBTTA)3(FDPO) (FDPO = 9,9‐bis (diphenylphosphorylphenyl) fluorene)‐codoped PMMA polymers with a mass ratio of 1:4 respectively, when they are spin‐coated as upper claddings, the relative gains of 2.2 and 1.8 dB cm−1 at 1067 nm are obtained in evanescent‐field waveguides with cross‐section of 4 × 8 µm2 under excitation of 300 mW 405 nm LED, and the gains of 3.9 and 4.9 dB cm−1 at 637 nm are achieved with pumping of 530 mW 450 nm LED respectively. By growing a 100 nm‐thick aluminum reflector with the waveguides, the optical gain at 1067 and 637 nm can be enhanced to 3.5 and 6.1 dB cm−1, corresponding to AQ(PhDPA)2‐Nd(DBTTA)3(DBFDPO) and AQ(PhDPA)2‐Nd(DBTTA)3(FDPO)‐codoped PMMA polymers, respectively.

Chelate phosphine oxide ligand (9,9‐dimethyl‐9H‐xanthene‐4,5‐diyl) bis (diphenylphosphineoxide) (XPO) is prepared as a neutral ligand to synthesize complex Nd (TTA)3 (XPO) (TTA = 2‐thenoyltrifluoroacetone). An appropriate energy gap between the XPO and TTA ligands, which can support two additional energy transfer routines from the first excited triplet state (T1) energy level of the XPO to that of the TTA, improves energy transfer in the Nd complex. Based on intramolecular energy transfer mechanism, optical gains at 1.06 and 1.31 µm are demonstrated in Nd (TTA)3 (XPO)‐doped polymer waveguides with the excitation of low‐power light‐emitting diodes (LEDs) instead of semiconductor lasers as pump sources. Using the vertical top‐pumping mode of a 365 nm LED, relative gains of 22.5 and 8.4 dB cm−1 are obtained at 1.06 and 1.31 µm, respectively, in a 0.2 cm long embedded waveguide with a cross‐section of 8 × 5 µm2. The active core layer is Nd (TTA)3 (XPO)‐doped SU‐8 polymer. Moreover, relative gains are achieved in evanescent‐field waveguide with a cross‐section of 6 × 4 µm2. The 21.0 and 5.6 dB cm−1 relative gains are achieved at 1.06 and 1.31 µm, respectively, with a net gain of 13.8 ± 0.3 dB cm−1 obtained at 1.06 µm in a 0.9 cm long SU‐8 waveguide with Nd (TTA)3 (XPO)‐doped polymethylmethacrylate as upper cladding.

Based on the intramolecular energy transfer mechanism between organic ligand TMHD (2, 2, 6, 6-tetramethyl-3, 5-heptanedione) and central Er3+ ions, optical gains at 1.55 µm were demonstrated in three structures of polymer waveguides using complex Er(TMHD)3-doped polymethylmethacrylate (PMMA) as the active material. With the excitation of two low-power UV light-emitting diodes (LEDs) instead of 980 or 1480 nm lasers, relative gains of 3.5 and 4.1 dB cm-1 were achieved in a 1-cm-long rectangular waveguide with an active core of Er(TMHD)3-doped PMMA polymer. Meanwhile, relative gain of 3.0 dB cm-1 was obtained in an evanescent-field waveguide with cross-section of 4 × 4 µm2 using passive SU-8 polymer as core and a ∼1-µm-thick Er(TMHD)3-doped PMMA as upper cladding. By growing a 100 nm thick aluminum mirror and active lower cladding, the optical gain was doubled to 6.7 dB cm-1 in evanescent-field waveguides because of the stimulated excitation of Er3+ ions in the upper and lower cladding and the improved absorption efficiency.

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