The TCST2103 transmissive sensor that includes a infrared emitter and photo transistor, located face-to-face on the optical axes in a leaded package which blocks visible light.
Had several left over as spares from a repair for a Chuff Trigger, the info may prove useful to someone.
What to do with them, constructed a Test PCB for further tinkering, may come in useful for a later Animation project, possible as switch on a Servo operated doors......
TCST 2103 Transmissive Optical Sensor with Photo transistor Output.