CRJ900 returns to departure airport when the nose gear failed to retract.

Narrative

We performed a normal take-off. When the PNF selected the gear handle to the up position; the nose gear stayed down. The indications in the flight deck were a nose gear down and locked green box; main gear unsafe yellow boxes; a red gear unsafe EICAS warning and a nose gear door open red EICAS warning. Upon completion of the after take-off checklist; I called for the gear unsafe non-normal checklist; and advised ATC that we would like vectors to remain in the vicinity of the airport while we dealt with a non-normal situation. We completed the non-normal checklist as it applied to our situation; and determined that we needed to return to our departure airport. I transferred control of the aircraft to the First Officer and called Dispatch. Dispatch agreed with the decision to return. Dispatch advised that as long as we could touch down with vertical speed less than 360 FPM; we could land with a gross weight up to 53000 LBS. At that time we were planning to land at 50;000 LBS. I advised the flight attendants that we were returning to our departure airport; and were expecting a normal landing. I then made a PA to the passengers. I accepted control of the aircraft from the First Officer. He advised ATC that we would be returning to our departure airport; and performed the descent and approach tasks. While being vectored for the approach; we discussed special considerations for the approach and landing. In light of the fact that I would be exercising emergency authority in landing the aircraft over max landing weight; I decided to declare an emergency with ATC. We landed; taxied to the gate and deplaned without further incident.