A series of simple Schiff bases, 2n-DHTC ((E)-N’-(2,n-dihydroxybenzylidene)-5-(thiophen-2-yl)isoxazole-3-carbohydrazide (n = 3,4,5,6)), with ICT characteristic were strategically constructed by rationally introducing 2,n-dihydroxybenzaldehyde (n = 3,4,5,6) into 5-(thiophen-2-yl)isoxazole-3-carbohydrazide and altering the position of another hydroxyl group. It was found that the position of the hydroxyl group on the dihydroxybenzaldehyde influence whether the sensor exhibited a colorimetric response, prompting further investigation into this phenomenon by DFT calculation. 25-DHTC, as a dual-emission fluorescent platform, demonstrated distinctive properties compared to other sensors, exhibiting ratiometric recognition towards Ga3+ ions and reversible fluorimetric quenching of Cu2+ ions in DMSO/H2O tris buffer. Meanwhile, limits of detection of 25-DHTC for Ga3+ and Cu2+ ions were as low as 15.0 nM and 2.4 nM, respectively. In addition, the 1:3 chelation stoichiometry between 25-DHTC and Ga3+/Cu2+ ions was confirmed, utilizing Job’s Plot analysis and mass spectrometric titration. The 25-DHTC sensor was employed to identify target ions in real water samples, while separate portable paper sensors were developed successfully for detecting Ga3+ ions. Subsequent visualization and assessment of real samples were performed through RGB analysis.