Room-temperature phosphorescent (RTP) materials can be used in anti-counterfeiting, organic light-emitting diodes and displays. However, designing RTP materials with a long luminescence lifetime and high solid-state emission efficiency is still a challenge. Due to the strong quantum confinement effect and the hydrogen bond network structure formed by polyamino sites, 0D RTP materials usually have a higher fluorescence quantum yield and longer phosphorescence lifetime. Here, we synthesized four manganese-based metal halides of different dimensions with a long lifetime and high luminous efficiency by changing organic cations: {[H2DAP]MnCl4}n (1, DAP = 1,3-propanediamine, 2D), {[(H2MELA)2MnCl5]Cl}n (2, MELA = melamine, 1D), [H2TAP]2MnCl6 (3, TAP = 2,4,6-triaminopyrimidine, 0D) and [H2MXD]2MnCl6 (4, MXD = m-xylylenediamine, 0D). [H2MXD]2MnCl6 (4) has a long lifetime (11 ms) and the maximum photoluminescence quantum yield (31.05%). Our work provides a new procedure for the development of RTP materials with high quantum yields.