Optical devices including resonant cavity structures

An electro-optical device comprising:

• a first electrode layer;
• a second electrode layer;
• and
• a middle layer disposed between the first electrode layer and the second electrode layer, the middle layer including a monolithic film of a material having the formula:
• [AaBbXxX′x′X″x″],
• A is cesium;
• B is tin;
• X, X′, and X″ are independently selected from fluorine, chlorine, bromine, and iodine;
• a is in the range of 1 to 9;
• b is in the range of 1 to 5;
• and
• a sum of x, x′, and x″ is in the range of 1 to 9.

An electro-optical device comprising:

• a first electrode layer;
• a second electrode layer;
• and
• a middle layer disposed between the first electrode layer and the second electrode layer, the middle layer including a monolithic film of a polycrystalline material having the formula:
• [AaBbXxX′x′X″x″][dopant],
• A is selected from potassium, rubidium, and cesium;
• B is selected from germanium, tin, and lead;
• X, X′, and X″ are independently selected from fluorine, chlorine, bromine, and iodine;
• a is in the range of 1 to 5;
• b is in the range of 1 to 3;
• and
• a sum of x, x′, and x″ is in the range of 1 to 5.