During the evolution of Casio calculators there were many different types of display.
I will try to put a timeline in Casio's concept of the calculator display's.
(This will not include other brands displays and only what Casio used)

Illuminating pad (1954-1959)

Nixie Tubes /cold-cathode display tube


amber gas-discharge individual display

amber gas-discharge single segment display (Casio 101-L)

VFD /Vacuum fluorescent displays

First generation vacuum fluorescent display (VFD) using a separate tube for each digit.

Second generation vacuum fluorescent display with all the digits in a single round tube.

Third generation vacuum fluorescent display with the digit assembly sandwiched between bonded glass plates.

Fourth generation vacuum fluorescent display in a flattened package made by welding a domed piece of glass onto a flat piece

Light Emitting Diode (RED) (casio 8E)

Liquid Crystal Displays (first generation)

Liquid Crystal Displays (Second generation) with black digits and a yellow background

Liquid Crystal Displays (Third Generation)

Colour Liquid Crystal Displays