Novo kept his cool to convert the decisive spot-kick after Alexander had saved from Fabio Liverani in a tense penalty shoot-out after 210 minutes of football failed to separate the two clubs over the two legs.
Rangers will now feature in their first European final since lifting the European Cup Winners' Cup back in 1972, when they face former boss Dick Advocaat's Zenit St Petersburg.
Rangers manager Walter Smith hailed his team's achievement after the match.
Smith told ITV4: "This takes a bit of beating - it's an emotional night. We were fantastic tonight in how we worked and prevented Fiorentina from scoring."
Smith continued: "It's the third lot of penalties we've had this season and we've managed to win them all - it's a magnificent achievement.
"We were hanging on a bit though tonight. Credit Fiorentina, they put us under a great deal of pressure.
"But I can't ask more of the boys - they defended fantastically."
Alexander said: "I'm lost for words, what an achievement. We were under the cosh and defended magnificently, the whole team defended well. I said to Barry (captain, Ferguson) 'If I could make one save' and I managed it. Then they put one over the bar."
Novo added: "I still can't believe it. It was a good performance by the team and it's so exciting for the fans."